psychology in the news - nichols...

Traces of Consciousness Foundin Some Patients Diagnosed as“Vegetative”LIEGE, BELGIUM, February 4, 2010. A 29-year-oldman thought to have been in a persistent vegetativestate for five years following a car accident has shownsigns of brain activity in response to questions fromdoctors. Most patients who are in a vegetative state canopen and move their eyes and may make sounds andfacial expressions, but they have no conscious aware-ness of themselves or their environment and cannotthink or reason.

The man is one of 54 patients with severe braindamage, resulting in their being either in a vegetative orminimally conscious state, who are being studied by aninternational team of scientists in England andBelgium. Researchers prompted them to imagine them-selves playing tennis or walking through the house theygrew up in, as their brains were being scanned by func-tional magnetic resonance imaging (MRI). Five of the54 were able to intentionally modulate their brain activ-ity in response to these prompts, just as healthy peoplein a control group could. The researchers then in-structed these five patients to respond to yes–no ques-tions by using one type of mental imagery (eitherplaying tennis or walking through the house) for “yes”and the other for “no.” Only the man who had been in-jured in the car accident was able to do this success-fully. He responded accurately to simple questions,such as whether his father’s name was Paul (yes) orAlexander (no), and whether he had ever been to theUnited States. Yet, at a bedside evaluation by a skilledclinical team, he showed no consciousness or ability tocommunicate.

Experts continue to debate just what these findingsmean for a patient’s state of cognition and conscious-ness. In 2009, Rom Houben, another victim of a carcrash who apparently was unconscious for 23 years,

Psychology in the Newsmade headlines when neurological tests indicated thathe too had some possible awareness, and a brain scanrevealed nearly normal activity in his brain. Therapistsprovided Houben with a computer touch screen thatseemed to allow him to communicate by spelling outwords. But skeptics pointed out that all of Houben’smessages were typed with the help of an aide who sup-ported and guided his hand. Scientific research has dis-credited such “facilitated communication” and hasfound that the typed messages come from the facilita-tor, not the patient. After watching a video of Houbensupposedly communicating as a facilitator guided hishand, bioethics expert Arthur Caplan commented, “Thatis Ouija board stuff.”

Nonetheless, these studies suggest that, in rarecases, patients with brain injury may have a greater de-gree of consciousness than previously believed possible.“With further development,” the researchers conclude,“this technique could be used by some patients toexpress their thoughts, control their environment, andincrease their quality of life.”

The Nervous System: A BasicBlueprint

Communication in the NervousSystem

Mapping the Brain

A Tour through the Brain

The Two Hemispheres of theBrain

Two Stubborn Issues in BrainResearch

Psychology in the News,Revisited

Taking Psychology with You:Cosmetic Neurology:Tinkering with the Brain

C H A P T E R

Neurons, Hormones, and the Brain

There is almost nothing that human beings fear more than having a con-

scious brain in a paralyzed head and body—with a brain that is alive

and functioning yet with no way to communicate to the outside world.

So it is no wonder that stories of people who seem to recover from comas or vege-

tative states after many years, or who show signs of brain activity when they were

previously thought to be brain dead, are both exciting and terrifying.

Incidents of apparent consciousness in vegetative patients raise all sorts of dif-

ficult medical, psychological, and ethical issues. How can we know for sure

whether a person has become incapable of higher mental function? Does brain-

scan technology offer an answer, or merely a possible clue? Will rare cases of

awareness give families false hope that their loved one is “really in there” when

the person actually lacks all cognitive function? Should a patient’s apparent

responses to yes–no questions be used to draw conclusions about whether the

person is in pain—or wants to live or die?

Cases of brain injury and disease vividly remind us that the 3-pound organ in-

side our skulls provides the bedrock for everything we do, feel, and think. Neuro-

psychologists, along with neuroscientists from other disciplines, study the brain

and the rest of the nervous system in hopes of gaining a better understanding of

normal behavior and of the outer reaches of what is possible for this organ. They

are concerned with the biological foundations of consciousness, perception,

memory, emotion, stress, and mental disorders—of everything, in fact, that

human beings feel and do. In this chapter, we will examine the structure of the

brain and the rest of the nervous system as background for our later discussions of

these and other topics.

At this very moment, your own brain, assisted by other parts of your nervous

system, is busily taking in these words. Whether you are excited, curious, or

bored, your brain is registering some sort of emotional reaction. As you continue

reading, your brain will (we hope) store away much of the information in this

chapter. Later on, your brain may enable you to smell a flower, climb the stairs, 113

114 CHAPTER 4 Neurons, Hormones, and the Brain

greet a friend, solve a problem, or chuckle at a joke.But the brain’s most startling accomplishment is itsknowledge that it is doing all these things. Thisself-awareness makes brain research different fromthe study of anything else in the universe. Scientistsmust use the cells, biochemistry, and circuitry oftheir own brains to understand the cells, biochem-istry, and circuitry of brains in general.

William Shakespeare called the brain “thesoul’s frail dwelling house.” Actually, this miracu-lous organ is more like the main room in a housefilled with many alcoves and passageways—the“house” being the nervous system as a whole.Before we can understand the windows, walls, andfurniture of this house, we need to becomeacquainted with the overall floor plan.

YOU are about to learn...• why you automatically pull your hand away from

something hot, without thinking.

• the major parts of the nervous system and their primaryfunctions.

The Nervous System: A Basic BlueprintThe function of a nervous system is to gather andprocess information, produce responses to stimuli,and coordinate the workings of different cells. Eventhe lowly jellyfish and the humble earthworm havethe beginnings of such a system. In very simpleorganisms that do little more than move, eat, andeliminate wastes, the “system” may be no more thanone or two nerve cells. In human beings, who do suchcomplex things as dance, cook, and take psychologycourses, the nervous system contains billions of cells.Scientists divide this intricate network into two mainparts: the central nervous system and the peripheral(outlying) nervous system (see Figure 4.1).

The Central Nervous SystemThe central nervous system (CNS) receives,processes, interprets, and stores incoming sensoryinformation—information about tastes, sounds,smells, color, pressure on the skin, the state ofinternal organs, and so forth. It also sends outmessages destined for muscles, glands, and internalorgans. The CNS is usually conceptualized as havingtwo components: the brain, which we will considerin detail later, and the spinal cord, which is actuallyan extension of the brain. The spinal cord runs fromthe base of the brain down the center of the back,protected by a column of bones (the spinal column),

and it acts as a bridge between the brain and the partsof the body below the neck.

The spinal cord produces some behaviors onits own without any help from the brain. Thesespinal reflexes are automatic, requiring no consciouseffort. If you accidentally touch a hot iron, you willimmediately pull your hand away, even before yourbrain has had a chance to register what has hap-pened. Nerve impulses bring a message to thespinal cord (hot!), and the spinal cord immediatelysends out a command via other nerve impulses,telling muscles in your arm to contract and to pullyour hand away from the iron. (Reflexes above theneck, such as sneezing and blinking, involve thelower part of the brain rather than the spinal cord.)

The neural circuits underlying many spinal re-flexes are linked to neural pathways that run up anddown the spinal cord, to and from the brain.

The study of this mysteri-ous 3-pound organ raisesmany challenging ques-tions. Why can a smallglitch in the brain’s cir-cuits be devastating tosome people, whereasothers can function withmajor damage? How doexperiences alter ourbrains? And where in thiscollection of cells and cir-cuits are the mind and oursense of self to be found?

Brain

Spinal cord

Nerves

FIGURE 4.1The Central and Peripheral Nervous SystemsThe central nervous system includes the brain and thespinal cord. The peripheral nervous system consists of43 pairs of nerves that transmit information to and from thecentral nervous system. Twelve pairs of cranial nerves inthe head enter the brain directly; 31 pairs of spinal nervesenter the spinal cord at the spaces between the vertebrae.

spinal cord A collectionof neurons and supportivetissue running from thebase of the brain downthe center of the back,protected by a columnof bones (the spinalcolumn).

central nervous sys-tem (CNS) The portionof the nervous systemconsisting of the brainand spinal cord.

CHAPTER 4 Neurons, Hormones, and the Brain 115

Because of these connections, reflexes can some-times be influenced by thoughts and emotions. Anexample is erection in men, a spinal reflex that canbe inhibited by anxiety or distracting thoughts andinitiated by erotic thoughts. Moreover, some re-flexes can be brought under conscious control. Ifyou concentrate, you may be able to keep your kneefrom jerking when it is tapped, as it normally would.Similarly, most men can learn to voluntarily delayejaculation, another spinal reflex. (Yes, they can.)

The Peripheral Nervous SystemThe peripheral nervous system (PNS) handles thecentral nervous system’s input and output. It con-tains all portions of the nervous system outside thebrain and spinal cord, right down to the nerves inthe tips of the fingers and toes. If your brain couldnot collect information about the world by means ofa peripheral nervous system, it would be like a radiowithout a receiver. In the peripheral nervous system,sensory nerves carry messages from special receptorsin the skin, muscles, and other internal and externalsense organs to the spinal cord, which sends themalong to the brain. These nerves put us in touchwith both the outside world and the activities of our

own bodies. Motor nerves carry orders from the cen-tral nervous system to muscles, glands, and internalorgans. They enable us to move, and they causeglands to contract and to secrete substances, includ-ing chemical messengers called hormones.

Scientists further divide the peripheral nervoussystem into two parts: the somatic (bodily) nervoussystem and the autonomic (self-governing) nerv-ous system. The somatic nervous system, sometimescalled the skeletal nervous system, consists of nervesthat are connected to sensory receptors—cells thatenable you to sense the world—and also to the skele-tal muscles that permit voluntary action. When youfeel a bug on your arm, or when you turn off a light orwrite your name, your somatic system is active. Theautonomic nervous system regulates the functioningof blood vessels, glands, and internal (visceral) organssuch as the bladder, stomach, and heart. When yousee someone you have a crush on and your heartpounds, your hands get sweaty, and your cheeks feelhot, you can blame your autonomic nervous system.

The autonomic nervous system is itself dividedinto two parts: the sympathetic nervous system andthe parasympathetic nervous system. These two partswork together, but in opposing ways, to adjust thebody to changing circumstances (see Figure 4.2).

peripheral nervoussystem (PNS) All por-tions of the nervous sys-tem outside the brain andspinal cord; it includessensory and motor nerves.

Sympathetic Division

Dilates pupilsWeakly stimulates salivationStimulates sweat glandsAccelerates heartbeatDilates bronchial tubes in lungsInhibits digestionIncreases epinephrine, norepinephrine secretion by adrenal glandsRelaxes bladder wallDecreases urine volumeStimulates glucose release by liverStimulates ejaculation in males

Parasympathetic Division

Constricts pupilsStimulates tear glandsStrongly stimulates salivationSlows heartbeatConstricts bronchial tubes in lungsActivates digestionInhibits glucose release by liver

Contracts bladder wallStimulates genital erection (both sexes) and vaginal lubrication (females)

FIGURE 4.2The Autonomic Nervous SystemIn general, the sympathetic division of the autonomic nervous system prepares the body toexpend energy and the parasympathetic division restores and conserves energy. Sympatheticnerve fibers exit from areas of the spinal cord (shown in red); parasympathetic fibers exit fromthe base of the brain and from spinal cord areas (shown in green).

somatic nervoussystem The subdivisionof the peripheral nervoussystem that connects tosensory receptors and toskeletal muscles; some-times called the skeletalnervous system.

parasympathetic nerv-ous system The subdivi-sion of the autonomicnervous system that oper-ates during relaxed statesand that conserves energy.

sympathetic nervoussystem The subdivisionof the autonomic nervoussystem that mobilizesbodily resources and in-creases the output of en-ergy during emotion andstress.

autonomic nervoussystem The subdivisionof the peripheral nervoussystem that regulates theinternal organs andglands.


The sympathetic system acts like the accelerator ofa car, mobilizing the body for action and an outputof energy. It makes you blush, sweat, and breathemore deeply, and it pushes up your heart rate andblood pressure. As we discuss in Chapter 13, whenyou are in a situation that requires you to fight, flee,or cope, the sympathetic nervous system whirls intoaction. The parasympathetic system is more like a

brake: It does not stop the body, of course, but itdoes tend to slow things down and keep them run-ning smoothly. It enables the body to conserve andstore energy. In everyday life, the two systems workin harmony. If you have to jump out of the way of aspeeding motorcyclist, sympathetic nerves increaseyour heart rate. Afterward, parasympathetic nervesslow it down again and keep its rhythm regular.

1.central: processes, interprets, and stores information and issues orders to muscles, glands, and organs2.peripheral: transmitsinformation to and from the CNS3.spinal cord: serves as a bridge between the brain and the peripheral nervous system, producesreflexes4.somatic: controls the skeletal muscles5.sympathetic: mobilizes the body for action, energy output6.parasympathetic:conserves energy, maintains the body in a quiet state

Pause now to mentally fill in the missing parts of the nervous system “house.” Then see whetheryou can briefly describe what each part of the system does.

Answers:

Quick Quiz

Brain

NervousSystem

NervousSystem

NervousSystem

AutonomicNervousSystem

??

?

NervousSystem

??

?

NervousSystem

NervousSystem

YOU are about to learn...• which cells function as the nervous system’s

communication specialists, and how they “talk” to eachother.

• the functions of glial cells, the most numerous cells inthe brain.

• why researchers are excited about the discovery of stemcells in the brain.

• how learning and experience alter the brain’scircuits.

• what happens when levels of neurotransmitters are toolow or too high.

• which brain chemicals mimic the effects of morphineby dulling pain and promoting pleasure.

• which hormones are of special interest to psychologists,and why.

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cell body The part of theneuron that keeps it aliveand determines whether itwill fire.


Communicationin the Nervous SystemThe blueprint we just described provides only ageneral idea of the nervous system’s structure. Nowlet’s turn to the details.

The nervous system is made up in part ofneurons, or nerve cells. They are the brain’s commu-nication specialists, transmitting information to,from, and within the central nervous system. Neu-rons are held in place by glia, or glial cells (from theGreek word for “glue”), which make up 90 percentof the brain’s cells.

Glial cells are more than just glue, however.They provide the neurons with nutrients, insulatethem, protect the brain from toxic agents, and re-move cellular debris when neurons die. They alsocommunicate chemically with each other and withneurons, and without them, neurons could notfunction effectively. One kind of glial cell appearsto give neurons the go-ahead to form connectionsand to start “talking” to each other (Ullian,Christopherson, & Barres, 2004). And over time,glia help determine which neural connections getstronger or weaker, suggesting that they play a vitalrole in learning and memory (Fields, 2004).

It’s neurons, however, that are considered thebuilding blocks of the nervous system, though instructure they are more like snowflakes than blocks,exquisitely delicate and differing from one anothergreatly in size and shape (see Figure 4.3). In the gi-raffe, a neuron that runs from the spinal cord downthe animal’s hind leg may be 9 feet long! Inthe human brain, neurons are microscopic.No one is sure how many neurons the humanbrain contains, but a typical estimate is100 billion, about the same number as thereare stars in our galaxy, and some estimates gomuch higher.

The Structure of the NeuronAs you can see in Figure 4.4, a neuron hasthree main parts: dendrites, a cell body, and anaxon. The dendrites look like the branches ofa tree; indeed, the word dendrite means “littletree” in Greek. Dendrites act like antennas,receiving messages from as many as 10,000other nerve cells and transmitting these mes-sages toward the cell body. They also dosome preliminary processing of those mes-sages. The cell body, which is shaped roughlylike a sphere or a pyramid, contains the bio-chemical machinery for keeping the neuron

alive. It also plays the key role in determiningwhether the neuron should fire—transmit a mes-sage to other neurons—depending on inputs fromother neurons. The axon (from the Greek for“axle”) transmits messages away from the cell body

FIGURE 4.3Different Kinds ofNeuronsNeurons vary in size andshape, depending on theirlocation and function.More than 200 types ofneurons have been identi-fied in mammals. Thisphoto shows neurons inthe outer layers of thebrain.

Spinal cord(motor neuron)

Thalamus Cerebellum Cortex

Cell body

Axon

Myelin sheath

Node

Synaptic endbulbs

Dendrites

Synapse

Axon terminals

FIGURE 4.4The Structure of a NeuronIncoming neural impulses are received by the dendrites of aneuron and are transmitted to the cell body. Outgoing signalspass along the axon to terminal branches.

neuron A cell thatconducts electrochemicalsignals; the basic unit ofthe nervous system; alsocalled a nerve cell.

glia [GLY-uh or GLEE-uh] Cells that support,nurture, and insulateneurons, remove debriswhen neurons die, en-hance the formation andmaintenance of neuralconnections, and modifyneuronal functioning.

dendrites A neuron’sbranches that receive in-formation from other neu-rons and transmit ittoward the cell body.


to other neurons or to muscle or gland cells. Axonscommonly divide at the end into branches calledaxon terminals. In adult human beings, axons varyfrom only four-thousandths of an inch to a few feetin length. Dendrites and axons give each neuron adouble role: As one researcher put it, a neuron isfirst a catcher, then a batter (Gazzaniga, 1988).

Many axons, especially the larger ones, are in-sulated by a surrounding layer of fatty materialcalled the myelin sheath, which in the central nerv-ous system is made up of glial cells. Constrictionsin this covering, called nodes, divide it into seg-ments, which make it look a little like a string oflink sausages (see Figure 4.4 again). One purposeof the myelin sheath is to prevent signals inadjacent cells from interfering with each other.Another, as we will see shortly, is to speed up theconduction of neural impulses. In individuals withmultiple sclerosis, loss of myelin causes erraticnerve signals, leading to loss of sensation, weaknessor paralysis, lack of coordination, or visionproblems.

In the peripheral nervous system, the fibers ofindividual neurons (axons and sometimes den-drites) are collected together in bundles callednerves, rather like the lines in a telephone cable.The human body has 43 pairs of peripheral nerves;one nerve from each pair is on the left side of thebody and the other is on the right. Most of thesenerves enter or leave the spinal cord, but 12 pairs inthe head, the cranial nerves, connect directly to thebrain. In Chapter 6, we will discuss cranial nervesthat are involved in the senses of smell, hearing,and vision.

Neurons in the NewsFor most of the twentieth century, scientists as-sumed that if neurons in the central nervous systemwere injured or damaged, they could never growback (regenerate). But then the conventional wis-dom got turned upside down. Animal studiesshowed that severed axons in the spinal cord can re-grow if you treat them with particular nervous sys-tem chemicals (Schnell & Schwab, 1990).Researchers are hopeful that regenerated axons willeventually enable people with spinal cord injuriesto use their limbs again.

In the past two decades, scientists have also hadto rethink another entrenched assumption: thatmammals produce no new CNS cells after infancy.In the early 1990s, Canadian neuroscientists, work-ing with mice, immersed immature cells from theanimals’ brains in a growth-promoting protein andshowed that these cells could give birth to new neu-

rons in a process called neurogenesis. Even more as-tonishing, the new neurons continued to divide andmultiply (Reynolds & Weiss, 1992). Since then, sci-entists have discovered that the human brain andother body organs also contain such cells, which arenow known as stem cells. Stem cells involved inlearning and memory seem to divide and maturethroughout adulthood. Animal studies find thatphysical exercise, effortful mental activity, and anenriched environment promote the production andsurvival of new cells, whereas aging and stress caninhibit their production and nicotine can kill them(Berger, Gage, & Vijayaraghavan, 1998; Kemper-mann, 2006; Shors, 2009).

Stem-cell research is one of the hottest areas inbiology and neuroscience. But in the United States,federal funding for basic stem-cell research hasfaced strong resistance by antiabortion activistswho are opposed to taking cells from embryos thatare a few days old, which consist of just a few cells.(Fertility clinics store many such embryos becauseseveral test-tube fertilizations are created for everypatient who hopes to become pregnant; eventually,the extra embryos are destroyed.) Embryonic stem(ES) cells are especially useful because they can dif-ferentiate into any type of cell, from neurons tokidney cells, whereas those from adults are morelimited and are harder to keep alive. Scientists havealso been able to reprogram cells from adult or-gans, most notably skin cells, to become stem cells(e.g., Takahashi et al., 2007; Yu et al., 2007). LikeES cells, these “induced pluripotent stem (iPS)cells” seem capable of giving rise to all types ofcells, although it is still unclear whether they willprove to be equally versatile; in one comparisontest, the embryonic stem cells made more than1,000 times more of the desired cells than did theiPS cell lines (Feng et al., 2010). Some scientistshave directly turned skin cells taken from the tailsof mice into neurons without first turning the cellsinto iPS cells (Vierbuchen et al., 2010). The nextstep will be to see if the same can be done withhuman cells.

Advocacy groups hope that transplanted stemcells will eventually help people recover from dis-eases of the brain (such as Parkinson’s) and fromdamage to the spinal cord and other parts of thebody. Scientists have already had some success inanimals. In one study, mice with recent spinal cordinjuries regained much of their ability to walk nor-mally after being injected with stem cells derivedfrom human fetal brain tissue. Microscopic analysisshowed that most of the cells had turned into eitherneurons or a particular type of glial cell (Cummingset al., 2005). In 2009, the FDA approved the first

Tiny stem cells like these(magnified 1,200 times inthis photo) have provokedboth excitement and con-troversy.

myelin sheath A fattyinsulation that maysurround the axon of aneuron.

nerves A bundle of nervefibers (axons and some-times dendrites) in theperipheral nervous system.

neurogenesis The pro-duction of new neuronsfrom immature stem cells.

stem cells Immaturecells that renew them-selves and have the poten-tial to develop into maturecells; given encouragingenvironments, stem cellsfrom early embryos candevelop into any cell type.

axon A neuron’s extend-ing fiber that conductsimpulses away from thecell body and transmitsthem to other neurons orto muscle or gland cells.

neurotransmitter Achemical substance thatis released by a transmit-ting neuron at the synapseand that alters the activityof a receiving neuron.


small U.S. trial with human patients with spinalcord injuries (Couzin, 2009).

A long road lies ahead, and many daunting tech-nical hurdles remain to be overcome before stem-cell research yields practical benefits for humanpatients. Increasing the rate of neurogenesis mayalleviate or improve some medical conditions buthave negative or no effects on others (Scharfman &Hen, 2007). We live in exciting times. Each yearbrings more incredible findings about neurons,findings that only a short time ago would haveseemed like science fiction.

How Neurons CommunicateNeurons do not directly touch each other, end toend. Instead, they are separated by a minusculespace called the synaptic cleft, where the axon termi-nal of one neuron nearly touches a dendrite or thecell body of another. The entire site—the axon ter-minal, the cleft, and the covering membrane of thereceiving dendrite or cell body—is called a synapse.Because a neuron’s axon may have hundreds oreven thousands of terminals, a single neuron mayhave synaptic connections with a great many oth-ers. As a result, the number of communication linksin the nervous system runs into the trillions or per-haps even the quadrillions.

Neurons speak to one another, or in some casesto muscles or glands, in an electrical and chemicallanguage. When a nerve cell is stimulated, a changein electrical potential occurs between the inside and

the outside of the cell. The physics of this processinvolves the sudden, momentary inflow of positivelycharged sodium ions across the cell’s membrane,followed by the outflow of positively charged potas-sium ions. The result is a brief change in electricalvoltage, called an action potential, which producesan electric current, or impulse.

If an axon is unmyelinated, the action potentialat each point in the axon gives rise to a new actionpotential at the next point; thus, the impulse travelsdown the axon somewhat as fire travels along thefuse of a firecracker. But in myelinated axons, theprocess is a little different. Conduction of a neuralimpulse beneath the sheath is impossible, in partbecause sodium and potassium ions cannot crossthe cell’s membrane except at the breaks (nodes)between the myelin’s “sausages.” Instead, the actionpotential “hops” from one node to the next. (Moreprecisely, the action potential regenerates at eachnode.) This arrangement allows the impulse totravel faster than it could if the action potential hadto be regenerated at every point along the axon.Nerve impulses travel more slowly in babies than inolder children and adults, because when babies areborn, the myelin sheaths on their axons are not yetfully developed.

When a neural impulse reaches the axon termi-nal’s buttonlike tip, it must get its message acrossthe synaptic cleft to another cell. At this point,synaptic vesicles, tiny sacs in the tip of the axon ter-minal, open and release a few thousand moleculesof a chemical substance called a neurotransmitter.Like sailors carrying a message from one island toanother, these molecules then diffuse across thesynaptic cleft (see Figure 4.5 on the next page).

When they reach the other side, the neuro-transmitter molecules bind briefly with receptor sites,special molecules in the membrane of the receivingneuron’s dendrites (or sometimes cell body), fittingthese sites much as a key fits a lock. Changes occurin the receiving neuron’s membrane, and the ulti-mate effect is either excitatory (a voltage shift in apositive direction) or inhibitory (a voltage shift in anegative direction), depending on which receptorsites have been activated. If the effect is excitatory,the probability that the receiving neuron will fireincreases; if it is inhibitory, the probability de-creases. Inhibition in the nervous system is ex-tremely important. Without it, we could not sleepor coordinate our movements. Excitation of thenervous system would be overwhelming, producingconvulsions.

What any given neuron does at any given mo-ment depends on the net effect of all the messagesbeing received from other neurons. Only when the

In an area associated with learning and memory,immature stem cells give rise to new neurons, andphysical and mental stimulation promotes the productionand survival of these neurons. These mice have toys toplay with, tunnels to explore, wheels to run on, and othermice to share their cage with. They will grow more cellsthan mice living alone in standard cages.

synapse The site wheretransmission of a nerveimpulse from one nervecell to another occurs;it includes the axonterminal, the synapticcleft, and receptor sitesin the membrane of thereceiving cell.

action potential A briefchange in electrical volt-age that occurs betweenthe inside and the outsideof an axon when a neuronis stimulated; it serves toproduce an electrical im-pulse.

FIGURE 4.6GettingConnectedNeurons in a new-born’s brain arewidely spaced, butthey immediatelybegin to form newconnections. Thesedrawings show themarked increase inthe number of con-nections from birthto age 15 months.


cell’s voltage reaches a certain threshold will it fire.Thousands of messages, both excitatory andinhibitory, may be coming into the cell, and thereceiving neuron must essentially average them.The message that reaches a final destination de-pends on the rate at which individual neuronsare firing, how many are firing, what types ofneurons are firing, where the neurons are located,and the degree of synchrony among different neu-rons. It does not depend on how strongly the individ-ual neurons are firing, however, because a neuronalways either fires or doesn’t. Like the turning on ofa light switch, the firing of a neuron is an all-or-noneevent.

The Plastic BrainWhen we are born, most of our synapses have notyet formed, but new synapses proliferate at a greatrate during infancy (see Figure 4.6). Axons and den-drites continue to grow, and tiny projections ondendrites, called spines, increase in size and number,producing more complex connections among thebrain’s nerve cells. Just as new learning and stimulat-ing environments promote the production of newneurons, they also produce increases in synapticcomplexity (Diamond, 1993; Greenough & Ander-son, 1991; Greenough & Black, 1992; Rosenzweig,1984). During childhood, unused synaptic connec-tions are also pruned away as cells or their branchesdie and are not replaced, leaving behind a more effi-cient neural network. These changes may help ex-plain why critical or sensitive periods for thedevelopment of some sensory and cognitive abilitiesoccur early in life. During these periods, acquisitionof these skills is amazingly rapid, but when the pe-riod ends, learning slows and may even become irre-versible (Thomas & Johnson, 2008). (We discusscritical periods in language development in Chapter3 and in visual development in Chapter 6.) Pruningand increases in synaptic density, however, are notconfined to childhood. They have another impor-tant developmental phase in adolescence and maycontinue all through life. For the most part, thebrain retains flexibility in adapting to new experi-ences, an adaptability neuroscientists call plasticity.

Plasticity is vividly demonstrated in cases ofpeople with brain damage who have experienced

Receivingneuron

Axonterminal

Synapticbulb

Synapticcleft

Neurotransmitter molecules

Receptorsites

Dendriteof receivingneuron

Synapticvesicles

Transmittingneuron

Neural impluse

FIGURE 4.5Neurotransmitter Crossing a SynapseNeurotransmitter molecules are released into the synaptic cleft between two neuronsfrom vesicles (chambers) in the transmitting neuron’s axon terminal. The molecules thenbind to receptor sites on the receiving neuron. As a result, the electrical state of thereceiving neuron changes and the neuron becomes either more likely to fire an impulseor less so, depending on the type of neurotransmitter.

At birth 3 months

6 months 15 months

plasticity The brain’sability to change andadapt in response toexperience, by reorganiz-ing or growing new neuralconnections.


remarkable recoveries—such as individuals whocannot recall simple words after a stroke but arespeaking normally within months, or who cannotmove an arm after a head injury but regain full useof the limb after physical therapy. Their brains haveapparently rewired themselves to adapt to the dam-age (Liepert et al., 2000).

When people who have been blind from birthor early childhood try to determine where a sound iscoming from, what happens in the part of the brainthat, in sighted people, processes visual informa-tion? In some blind people, might regions normallydevoted to vision begin to process input from othersenses instead? Using brain-scan technology, a teamof researchers examined the brains of people as theylocalized sounds heard through speakers (Gougouxet al., 2005). Some participants were sighted andothers had been blind from early in life. When theparticipants heard sounds through both ears, activ-ity in the occipital cortex, an area associated with vi-sion, decreased in the sighted people but not in theblind ones. When one ear was plugged, blind partic-ipants who did especially well at localizing soundsshowed activation in two areas of the occipital cor-tex; neither sighted people nor blind people with or-dinary ability showed such activation. The degree ofactivation in these regions was correlated with theblind people’s accuracy on the task, suggesting thattheir brains had adapted to blindness by recruitingvisual areas to take part in activities involving hear-ing—a dramatic example of plasticity.

Building on this research, the researchers won-dered what would happen if sighted people wereblindfolded for five days and had to adapt to theirtemporary inability to see. Before donning theblindfolds, the volunteers’ brain scans showed thatthe visual areas in their brains were quiet duringtasks requiring hearing or touch. By the fifth day,however, these areas were lighting up during thetasks. Then, after the blindfolds were removed, thevisual centers once again quieted down (Pascual-Leone et al., 2005). The visual areas of the brainapparently possess the computational machinerynecessary for processing nonvisual information, butthis machinery remains dormant until circum-stances require its activation (Amedi et al., 2005).When people have been blind for most of theirlives, new connections may form, permitting last-ing structural changes in the brain’s wiring.

This research teaches us that the brain is a dy-namic organ: Its circuits are continually beingmodified in response to information, challenges,and changes in the environment. As scientists cometo understand this process better, they may be ableto apply their knowledge by designing improved

rehabilitation programs for people with sensoryimpairments, developmental disabilities, and braininjuries.

Chemical Messengers in the Nervous SystemThe nervous system “house” would remain foreverdark and lifeless without chemical couriers such asthe neurotransmitters. Let’s look more closely nowat these substances and at two other types of chem-ical messengers: endorphins and hormones.

Neurotransmitters: Versatile Couriers Aswe have seen, neurotransmitters make it possible forone neuron to excite or inhibit another. Neuro-transmitters exist not only in the brain but also inthe spinal cord, the peripheral nerves, and certainglands. Through their effects on specific nerve cir-cuits, these substances can affect mood, memory,and well-being. The nature of the effect depends onthe level of the neurotransmitter, its location, andthe type of receptor it binds with. Here are a few ofthe better-understood neurotransmitters and someof their known or suspected effects:

• Serotonin affects neurons involved in sleep, ap-petite, sensory perception, temperature regula-tion, pain suppression, and mood.

• Dopamine affects neurons involved in voluntarymovement, learning, memory, emotion, pleasureor reward, and, possibly, response to novelty.

• Acetylcholine affects neurons involved in muscle ac-tion, cognitive functioning, memory, and emotion.

• Norepinephrine affects neurons involved in in-creased heart rate and the slowing of intestinalactivity during stress, and neurons involved inlearning, memory, dreaming, waking from sleep,and emotion.

• GABA (gamma-aminobutyric acid) is the major in-hibitory neurotransmitter in the brain.

• Glutamate is the major excitatory neurotransmit-ter in the brain; it is released by about 90 percentof the brain’s neurons.

Harmful effects can occur when neurotrans-mitter levels are too high or too low. AbnormalGABA levels have been implicated in sleep and eat-ing disorders and in convulsive disorders, includingepilepsy. People with Alzheimer’s disease lose braincells responsible for producing acetylcholine andother neurotransmitters, and these deficits helpaccount for their devastating memory problems. Aloss of cells that produce dopamine is responsiblefor the tremors and rigidity of Parkinson’s disease.In multiple sclerosis, immune cells overproduce

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glutamate, which damages or kills glial cells thatnormally make myelin.

We want to warn you, however, that pinningdown the relationship between neurotransmitterabnormalities and behavioral or physical abnormali-ties is extremely tricky. Each neurotransmitter playsmultiple roles, and the functions of different sub-stances often overlap. Further, it is always possiblethat something about a disorder leads to abnormalneurotransmitter levels instead of the other wayaround. For example, although drugs that boost ordecrease levels of particular neurotransmitters aresometimes effective in treating some mental disor-ders, such as depression, this fact does not neces-sarily mean that abnormal neurotransmitter levelscause the disorders. After all, aspirin can relieve aheadache, but headaches are not caused by a lack ofaspirin!

Many of us regularly ingest things that affectour own neurotransmitters. Even ordinary foods caninfluence the availability of neurotransmitters in thebrain. Most recreational drugs produce their effectsby blocking or enhancing the actions of neurotrans-mitters. So do some herbal remedies. St. John’s wort,which is often taken for depression, prevents thecells that release serotonin from reabsorbing excessmolecules that have remained in the synaptic cleft; asa result, serotonin levels rise. Many people do notrealize that such remedies, because they affect thenervous system’s biochemistry, can interact withother medications and can be harmful in high doses.

Endorphins: The Brain’s Natural OpiatesAnother intriguing group of chemical messengers isknown collectively as endogenous opioid peptides, ormore popularly as endorphins. Endorphins haveeffects similar to those of natural opiates; that is,they reduce pain and promote pleasure. They arealso thought to play a role in appetite, sexual activ-ity, blood pressure, mood, learning, and memory.Some endorphins function as neurotransmitters,

but most of them act primarily by limiting, prolong-ing, or altering the effects of neurotransmitters.

Endorphin levels seem to shoot up when an an-imal or a person is afraid or under stress. This is noaccident; by making pain bearable in such situa-tions, endorphins give a species an evolutionary ad-vantage. When an organism is threatened, it needsto do something fast. Pain, however, can interferewith action: A mouse that pauses to lick a woundedpaw may become a cat’s dinner; a soldier who isovercome by an injury may never get off the battle-field. But, of course, the body’s built-in system ofcounteracting pain is only partly successful, espe-cially when painful stimulation is prolonged.

In Chapter 14, we will see that a link also existsbetween endorphins and human attachment. Re-search with animals suggests that, in infancy, contactwith the mother stimulates the flow of endorphins,which strengthens the infant’s bond with her. Someresearchers now think that this endorphin rush alsooccurs in the early stages of passionate love betweenadults, accounting for the feeling of euphoria that“falling” for someone creates (Diamond, 2004).

Hormones: Long-Distance MessengersHormones, which make up the third class of chemi-cal messengers, are produced primarily inendocrine glands. They are released directly intothe bloodstream, which carries them to organs andcells that may be far from their point of origin.Hormones have dozens of jobs, from promotingbodily growth to aiding digestion to regulatingmetabolism. Neurotransmitters and hormones arenot always chemically distinct; the two classifica-tions are like social clubs that admit some of thesame members. A particular chemical, such asnorepinephrine, may belong to more than oneclassification, depending on where it is located andwhat function it is performing. Nature has been ef-ficient, giving some substances more than one task.

Former heavyweightchampion Muhammad Aliand actor Michael J. Foxboth have Parkinson’s dis-ease, which involves a lossof dopamine-producingcells. They have used theirfame to draw public atten-tion to the disorder.

endorphins [en-DOR-fins] Chemical sub-stances in the nervoussystem that are similar instructure and action toopiates; they are involvedin pain reduction, pleas-ure, and memory and areknown technically asendogenous opioidpeptides.

hormones Chemicalsubstances, secreted byorgans called glands, thataffect the functioning ofother organs.

endocrine glandsInternal organs thatproduce hormones andrelease them into thebloodstream.


The following hormones, among others, are ofparticular interest to psychologists:

1Melatonin, which is secreted by the pineal glanddeep within the brain, helps to regulate daily

biological rhythms and promotes sleep, as we dis-cuss in Chapter 5.

2Oxytocin, which is secreted by another smallgland in the brain, the pituitary gland, enhances

uterine contractions during childbirth and facili-tates the ejection of milk during nursing. Psycholo-gists are interested in this hormone because, alongwith another hormone called vasopressin, it alsocontributes to relationships in both sexes by pro-moting attachment and trust (see Chapter 14).

3Adrenal hormones, which are produced by theadrenal glands (organs that are perched right

above the kidneys), are involved in emotion andstress (see Chapter 13). These hormones also rise inresponse to other conditions, such as heat, cold,pain, injury, burns, and physical exercise, and in re-sponse to some drugs, such as caffeine and nicotine.The outer part of each adrenal gland producescortisol, which increases blood-sugar levels andboosts energy. The inner part produces epinephrine(commonly known as adrenaline) and norepinephrine.When adrenal hormones are released in your body,activated by the sympathetic nervous system, theyincrease your arousal level and prepare you for ac-tion. Adrenal hormones also enhance memory, aswe discuss in Chapter 8.

4Sex hormones, which are secreted by tissue inthe gonads (testes in men, ovaries in women)

and also by the adrenal glands, include three maintypes, all occurring in both sexes but in differingamounts and proportions in males and females afterpuberty. Androgens (the most important of which istestosterone) are masculinizing hormones producedmainly in the testes but also in the ovaries and theadrenal glands. Androgens set in motion the physi-cal changes males experience at puberty—notably adeepened voice and facial and chest hair—andcause pubic and underarm hair to develop in bothsexes. Testosterone also influences sexual arousal inboth sexes. Estrogens are feminizing hormones thatbring on physical changes in females at puberty,such as breast development and the onset of men-struation, and that influence the course of the men-strual cycle. Progesterone contributes to the growthand maintenance of the uterine lining in prepara-tion for a fertilized egg, among other functions. Es-trogens and progesterone are produced mainly inthe ovaries but also in the testes and the adrenalglands.

Researchers are studying the possible in-volvement of sex hormones in behavior not linkedto sex or reproduction. The body’s natural estro-gen may contribute to learning and memory inboth sexes by promoting the formation of synap-tic connections in areas of the brain (Lee &McEwen, 2001; Maki & Resnick, 2000; Sherwin,1998a). But the common belief that fluctuatinglevels of estrogen and progesterone make mostwomen “emotional” before menstruation has notbeen supported by research, as we discuss inChapter 5.

melatonin A hormone,secreted by the pinealgland, that is involved inthe regulation of daily bio-logical rhythms.

oxytocin A hormone, se-creted by the pituitarygland, that stimulatesuterine contractions dur-ing childbirth, facilitatesthe ejection of milk duringnursing, and seems to pro-mote, in both sexes, at-tachment and trust inrelationships.

adrenal hormonesHormones that are pro-duced by the adrenalglands and that are in-volved in emotion andstress.

sex hormonesHormones that regulatethe development andfunctioning of reproduc-tive organs and that stim-ulate the development ofmale and female sexualcharacteristics; they in-clude androgens, estro-gens, and progesterone.

A. 1.neurons2.dendrites3.synapse4.endorphin5.neurotransmitters6.epinephrineB.You might want to ask, among otherthings, about side effects (each neurotransmitter has several functions, all of which might be affected by the treatment); evidence thatthe treatment works; whether there is any reason to believe that your own neurotransmitter levels are abnormal; and whether there maybe other reasons for your depression.

Get your glutamate going by taking this quiz.

A. Which word in parentheses better fits each of the following definitions?

1. Basic building blocks of the nervous system (nerves, neurons)

2. Cell parts that receive nerve impulses (axons, dendrites)

3. Site of communication between neurons (synapse, myelin sheath)

4. Opiatelike substance in the brain (dopamine, endorphin)

5. Chemicals that make it possible for neurons to communicate (neurotransmitters, hormones)

6. Hormone closely associated with emotional excitement (epinephrine, estrogen)

B. Imagine that you are depressed, and you hear about a treatment for depression that affects the levels ofseveral neurotransmitters thought to be involved in the disorder. Based on what you have learned, whatquestions would you want to ask before deciding whether to try the treatment?

Answers:

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YOU are about to learn...• why patterns of electrical activity in the brain are called

“brain waves.”

• how scanning techniques reveal changes in brainactivity while people listen to music, solve mathproblems, or do other activities.

• the limitations of brain scans as a way of understandingthe brain.

Mapping the BrainWe come now to the main room of the nervous sys-tem house: the brain. A disembodied brain stored ina formaldehyde-filled container is a putty-colored,wrinkled glob of tissue that looks a little like anoversized walnut. It takes an act of imagination toenvision this modest-looking organ writing Hamlet,discovering radium, or inventing the paper clip.

In a living person, of course, the brain isencased in a thick protective vault of bone. How,then, can scientists study it? One approach is tostudy patients who have had a part of the braindamaged or removed because of disease or injury.Another, the lesion method, involves damaging orremoving sections of brain in animals and thenobserving the effects.

Electrical and Magnetic Detection Thebrain can also be probed with devices calledelectrodes. Some electrodes are coin-shaped and aresimply pasted or taped onto the scalp. They detectthe electrical activity of millions of neurons in par-ticular regions of the brain and are widely used inresearch and medical diagnosis. The electrodes areconnected by wires to a machine that translates theelectrical energy from the brain into wavy lines on amoving piece of paper or visual patterns on ascreen. That is why electrical patterns in the brainare known as “brain waves.” Different wave pat-terns are associated with sleep, relaxation, andmental concentration (see Chapter 5).

A brain-wave recording is called anelectroencephalogram (EEG). A standard EEG isuseful but not very precise because it reflects the ac-tivities of many cells at once. “Listening” to thebrain with an EEG machine is like standing outsidea sports stadium: You know when something is hap-pening, but you can’t be sure what it is or who isdoing it. Fortunately, computer technology can becombined with EEG technology to get a clearerpicture of brain activity patterns associated withspecific events and mental processes. The com-puter suppresses all the background noise, leaving

only the pattern of electrical response to the eventbeing studied.

For even more precise information, researchersuse needle electrodes, very thin wires or hollow glasstubes that can be inserted into the brain, either di-rectly in an exposed brain or through tiny holes inthe skull. Only the skull and the membranes cover-ing the brain need to be anesthetized; the brain itself,which processes all sensation and feeling, paradoxi-cally feels nothing when touched. Therefore, ahuman patient or an animal can be awake and notfeel pain during the procedure. Needle electrodescan be used both to record electrical activity from thebrain and to stimulate the brain with weak electricalcurrents. Stimulating a given area often results in aspecific sensation or movement. Microelectrodes areso fine that they can be inserted into single cells.

A newer method of stimulating the brain,transcranial magnetic stimulation (TMS), delivers alarge current through a wire coil placed on a per-son’s head. The current produces a magnetic fieldabout 40,000 times greater than the earth’s naturalmagnetic field. This procedure causes neuronsunder the coil to fire. It can be used to producemotor responses (say, a twitch in the thumb or aknee jerk) and can also be used by researchers tobriefly inactivate an area and observe the effects onbehavior—functioning, in effect, as a virtual (andtemporary) lesion method. The drawback is thatwhen neurons fire, they cause many other neuronsto become active too, so it is often hard to tellwhich neurons are critical for a particular task.TMS has also been used to treat depression (seeChapter 12), but there is little reliable evidence ofits effectiveness so far.

Electrodes are used toproduce an overall pictureof electrical activity in dif-ferent areas of the brain.

This microelectrode is being used to record the electricalimpulses generated by a single cell in the brain of amonkey.

electroencephalogram(EEG) A recording ofneural activity detectedby electrodes.

transcranial magneticstimulation (TMS) Amethod of stimulatingbrain cells, using apowerful magnetic fieldproduced by a wire coilplaced on a person’shead; it can be used byresearchers to temporarilyinactivate neural circuitsand is also being usedtherapeutically.


Scanning the Brain Since the mid-1970s, manyother amazing doors to the brain have opened. ThePET scan (positron-emission tomography) goes be-yond anatomy to record biochemical changes in thebrain as they are happening. One type of PET scantakes advantage of the fact that nerve cells convertglucose, the body’s main fuel, into energy. Aresearcher can inject a person with a glucoselikesubstance that contains a harmless radioactive ele-ment. This substance accumulates in brain areasthat are particularly active and are therefore con-suming glucose rapidly. The substance emits radia-tion, which is detected by a scanning device, andthe result is a computer-processed picture of bio-chemical activity on a display screen, with differentcolors indicating different activity levels. Otherkinds of PET scans measure blood flow or oxygenconsumption, which also reflect brain activity.

PET scans, which were originally designed todiagnose abnormalities, have produced evidencethat some brain areas in people with emotional dis-orders are either unusually quiet or unusually ac-tive. But PET technology can also show whichparts of the brain are active during ordinary activi-ties and emotions. It lets researchers see whichareas are busiest when a person hears a song, recallsa sad memory, works on a math problem, or shiftsattention from one task to another. The PET scansin Figure 4.7a show what an average brain lookslike when a person is doing various tasks.

Another technique, MRI (magnetic resonanceimaging), allows the exploration of inner spacewithout injecting chemicals. Powerful magneticfields and radio frequencies are used to produce

vibrations in the nuclei of atoms making up bodyorgans. The vibrations are then picked up as signalsby special receivers. A computer analyzes the sig-nals, taking into account their strength and dura-tion, and converts them into a high-contrastpicture of the organ (see Figure 4.7b). An ultrafastversion of MRI, called functional MRI (fMRI), cancapture brain changes many times a second as aperson performs a task, such as reading a sentenceor solving a puzzle. Today, thousands of facilitiesacross the United States are using MRIs forresearch and assessment.

Other methods are becoming available witheach passing year. Researchers are using fMRIscans, in particular, to correlate activity in specificbrain areas with everything from racial attitudesto moral reasoning to spiritual meditation.Researchers in an applied field called “neuromar-keting” are even using them to study which parts ofthe brain are activated while people watch TVcommercials or political ads.

Controversies and Cautions Exciting thoughthese developments and technologies are, we needto understand that technology cannot replace criti-cal thinking (Wade, 2006). Because brain-scan im-ages seem so “real” and scientific, many people failto realize that these images can convey oversimpli-fied and sometimes misleading impressions. Bymanipulating the color scales used in PET scans,researchers can either accentuate or minimize con-trasts between two brains. Small contrasts can bemade to look dramatic, larger ones to look insignif-icant. An individual’s brain can even be made to

FIGURE 4.7Scanning the BrainIn the PET scans on the left, arrows and the color red indicate areas of highest activity, and violet indicates areas oflowest activity, as a person does different things. On the right, an MRI shows a child’s brain, along with the bottle hewas drinking from while the image was obtained.

PET scan (positron-emission tomography)A method for analyzingbiochemical activity in thebrain, using injections of aglucoselike substancecontaining a radioactiveelement.

MRI (magnetic reso-nance imaging) Amethod for studying bodyand brain tissue, usingmagnetic fields andspecial radio receivers;functional MRI (fMRI) is afaster form often used inpsychological research.

(a) (b)

medulla [muh-DUL-uh] A structure in thebrain stem responsible forcertain automatic func-tions, such as breathingand heart rate.


appear completely different depending onthe colors used, as the photographs inFigure 4.8 show (Dumit, 2004).

Further, in fMRI studies, questionablestatistical procedures have often producedhighly inflated correlations between brainactivity and measures of personality andemotion (Vul et al., 2009). Yet the pressusually reports these findings uncritically,giving the impression that neuroscientistsknow more about the relationship betweenthe brain and psychological processes thanthey really do.

There is a final reason for cautionabout these methods: As of yet, brain scansdo not tell us precisely what is happeninginside a person’s head, either mentally orphysiologically. They tell us where things

happen, but not why or how they happen—howdifferent circuits connect to produce behavior.Enthusiasm for technology has produced a moun-tain of findings, but it has also resulted in someunwarranted conclusions about “brain centers” or“critical circuits” for this or that behavior. If youknow that one part of the brain is activated whenyou are thinking hot thoughts of your beloved,what exactly do you know about love? Does that

part also light up whenyou are watching a hotlove scene in a movie,looking at a luscious hotfudge sundae, or think-

ing about happily riding your horse Horacethrough the hills?

For these reasons, one neuroscientist has calledthe search for brain centers and circuits “the newphrenology” (Uttal, 2001). Another drew this anal-ogy (cited in Wheeler, 1998): A researcher scansthe brains of gum-chewing volunteers, finds outwhich parts of their brains are active, and concludesthat she has found the brain’s “gum-chewingcenter”!

Even if there were a gum-chewing center, yoursmight not be in the same place as someone else’s.Each brain is unique for two reasons: First, a uniquegenetic package is present in each of us at birth; sec-ond, a lifetime of experiences and sensations is con-stantly altering the brain’s biochemistry and neuralnetworks. Thus, if you are a string musician, thearea in your brain associated with music productionis likely to be larger than that of nonmusicians; theearlier in life you started to play, the larger itbecomes (Jancke, Schlaug, & Steinmetz, 1997). Andif you are a cab driver, the area in your hippocampusresponsible for visual representations of the

environment is likely to be larger than average(Maguire et al., 2000). Technological measurementsoften promote the incorrect view that all brains arealike—if we scan a few, we understand them all.

Nonetheless, scans do provide an exciting lookat the brain at work and play, and we will be reportingmany findings from PET scan and fMRI researchthroughout this book. The brain can no longer hidefrom researchers behind the fortress of the skull.

YOU are about to learn...• the major parts of the brain and some of their major

functions.

• why it is a good thing that the outer covering of thehuman brain is so wrinkled.

• how a bizarre nineteenth-century accident illuminatedthe role of the frontal lobes.

A Tour through the BrainMost modern brain theories assume that differentbrain parts perform different (though greatly over-lapping) tasks. This concept, known as localizationof function, goes back at least to Joseph Gall(1758–1828), the Austrian anatomist who thoughtthat personality traits were reflected in the develop-ment of specific areas of the brain. Gall’s theory ofphrenology was completely wrong-headed (so tospeak), but his general notion of specialization inthe brain had merit.

To learn about what the major brain structuresdo, let’s take an imaginary stroll through the brain.Pretend that you have shrunk to a microscopic sizeand that you are wending your way through the“soul’s frail dwelling house,” starting at the lowerpart, just above the spine. Figure 4.9 shows themajor structures we will encounter along our tour;you may want to refer to it as we proceed. But keepin mind that any activity—feeling an emotion, hav-ing a thought, performing a task—involves manydifferent structures. Our description, therefore, is asimplification.

The Brain StemWe begin at the base of the skull with the brainstem, which began to evolve some 500 million yearsago in segmented worms. The brain stem looks likea stalk rising out of the spinal cord. Pathways to andfrom upper areas of the brain pass through its twomain structures: the medulla and the pons. Thepons is involved in (among other things) sleeping,waking, and dreaming. The medulla is responsible

FIGURE 4.8Coloring the BrainBy altering the colors usedin a PET scan, researcherscan create the appearanceof dramatic brain differ-ences. These scans areactually images of thesame brain.

Thinking Criticallyabout BrainTechnology

localization offunction Specializationof particular brain areasfor particular functions.

brain stem The part ofthe brain at the top of thespinal cord, consisting ofthe medulla and the pons.

pons A structure in thebrain stem involved in,among other things,sleeping, waking, anddreaming.

thalamus A brainstructure that relayssensory messages to thecerebral cortex.

cerebellum A brainstructure that regulatesmovement and balanceand is involved in somecognitive tasks.

reticular activatingsystem (RAS) A densenetwork of neurons foundin the core of the brainstem; it arouses the cortexand screens incominginformation.


Cerebral cortex

Thalamus

Cerebellum

Medulla

Pons

Reticular activatingsystem

Pituitary gland

Hypothalamus

Corpus callosum

Cerebrum

FIGURE 4.9Major Structures of the Human BrainThis cross section depicts the brain as if it were split in half. The view is of the insidesurface of the right half, and it shows the structures described in the text.

for bodily functions that do not have to be con-sciously willed, such as breathing and heart rate.Hanging has long been used as a method of execu-tion because when it breaks the neck, nerve path-ways from the medulla are severed, stoppingrespiration.

sends signals that the thalamus sends on to an audi-tory area. The only sense that completely bypassesthe thalamus is the sense of smell, which has its ownprivate switching station, the olfactory bulb. The ol-factory bulb lies near areas involved in emotion.Perhaps that is why particular odors—the smell offresh laundry, gardenias, a steak sizzling on thegrill—often rekindle vivid memories.

Cerebellum

Pons

Medulla

Reticular activating system

Extending upward from the core of the brainstem is the reticular activating system (RAS). Thisdense network of neurons, which extends above thebrain stem into the center of the brain and hasconnections with areas that are higher up, screensincoming information and arouses the higher cen-ters when something happens that demands theirattention. Without the RAS, we could not be alertor perhaps even conscious.

The CerebellumStanding atop the brain stem and looking toward theback part of the brain, we see a structure about thesize of a small fist. It is the cerebellum, or “lesserbrain,” which contributes to a sense of balance andcoordinates the muscles so that movement is smoothand precise. If your cerebellum were damaged, youwould probably become exceedingly clumsy and un-coordinated. You might have trouble using a pencil,threading a needle, or even walking. In addition, thisstructure is involved in remembering simple skillsand acquired reflexes. But the cerebellum, which wasonce considered just a motor center, is not as “lesser”as its name implies: It plays a part in such complexcognitive tasks as analyzing sensory information,solving problems, and understanding words.

The ThalamusDeep in the brain’s interior, roughly at its center,we can see the thalamus, the busy traffic officer ofthe brain. As sensory messages come into the brain,the thalamus directs them to higher areas: Thesight of a sunset sends signals that the thalamusdirects to a vision area, and the sound of an oboe

Thalamus

Olfactorybulb

The Hypothalamus and thePituitary GlandBeneath the thalamus sits a structure called thehypothalamus (hypo means “under”). It is involved in

hypothalamus A brainstructure involved inemotions and drives vitalto survival, such as fear,hunger, thirst, and repro-duction; it regulates theautonomic nervoussystem.

cerebrum [suh-REE-brum] The largest brainstructure, consisting ofthe upper part of thebrain; divided into twohemispheres, it is incharge of most sensory,motor, and cognitiveprocesses. From the Latinfor “brain.”

limbic system A groupof brain areas involved inemotional reactions andmotivated behavior.

pituitary gland A smallendocrine gland at thebase of the brain thatreleases many hormonesand regulates otherendocrine glands.


drives associated with the survival of both the indi-vidual and the species—hunger, thirst, emotion, sex,and reproduction. It regulates body temperature bytriggering sweating or shivering, and it controls thecomplex operations of the autonomic nervous sys-tem. It also contains the biological clock that con-trols the body’s daily rhythms (see Chapter 5).

Hanging down from the hypothalamus, con-nected to it by a short stalk, is a cherry-sized en-docrine gland called the pituitary gland, mentionedearlier in our discussion of hormones. The pituitaryis often called the body’s “master gland” becausethe hormones it secretes affect many other en-docrine glands. The master, however, is really onlya supervisor. The true boss is the hypothalamus,which sends chemicals to the pituitary that tell itwhen to “talk” to the other endocrine glands. Thepituitary, in turn, sends hormonal messages out tothese glands.

The hypothalamus, along with the two struc-tures we will come to next, has often been consid-ered part of a loosely interconnected set ofstructures called the limbic system, shown inFigure 4.10. (Limbic comes from the Latin word for“border”: These structures form a sort of borderbetween the higher and lower parts of the brain.)Some anatomists also include parts of the thalamusin this system. Structures in this region are heavilyinvolved in emotions that we share with other ani-mals, such as rage and fear (MacLean, 1993). Theusefulness of speaking of the limbic system as an in-tegrated set of structures is now in dispute, becausethese structures also have other functions, andbecause parts of the brain outside of the limbic sys-tem are involved in emotion. However, the termlimbic system is still in wide use among researchers,so we thought you should know it.

The AmygdalaThe amygdala (from the ancient Greek word for“almond”) is responsible for evaluating sensoryinformation, quickly determining its emotional

importance, and contributing to the initial decisionto approach or withdraw from a person or situation(see Chapter 13). It instantly assesses danger orthreat, and it plays an important role in mediatinganxiety and depression; PET scans find that de-pressed and anxious patients show increased neuralactivity in this structure (Davidson et al., 1999;Drevets, 2000). In addition, the amygdala is in-volved in forming and retrieving emotional memo-ries (see Chapter 8).

The HippocampusAnother important area traditionally classified aslimbic is the hippocampus, whose shape must havereminded someone of a sea horse, for in Latin, that iswhat its name means. This structure compares sen-sory information with what the brain has learned toexpect about the world. When expectations are met,it tells the reticular activating system to cool it.There’s no need for neural alarm bells to go off everytime a car goes by, a bird chirps, or you feel yoursaliva trickling down the back of your throat!

The hippocampus has also been called the“gateway to memory.” It enables us to form spatialmemories so that we can accurately navigatethrough our environment. And, along with adjacentbrain areas, it enables us to form new memoriesabout facts and events—the kind of informationyou need to identify a flower, tell a story, or recall avacation trip. The information is then stored in thecerebral cortex, which we will be discussing shortly.When you recall meeting someone yesterday,

Pituitarygland

Hypothalamus

Cingulate gyrus Fornix

Septal nuclei

Mammilary body

Amygdala

Hippocampus

FIGURE 4.10The Limbic SystemStructures of the limbic system play an important rolein memory and emotion. The text describes two of thesestructures, the amygdala and the hippocampus. Thehypothalamus is also often included as part of thelimbic system.

amygdala [uh-MIG-dul-uh] A brain structureinvolved in the arousaland regulation of emotionand the initial emotionalresponse to sensoryinformation.

hippocampus A brainstructure involved in thestorage of new informationin memory.

cerebral cortex Acollection of several thinlayers of cells covering thecerebrum; it is largelyresponsible for highermental functions. Cortexis Latin for “bark” or“rind.”

lateralization Specializa-tion of the two cerebralhemispheres for particularoperations.

corpus callosum[CORE-puhs cah-LOW-suhm] The bundle ofnerve fibers connectingthe two cerebralhemispheres.

cerebral hemispheresThe two halves of thecerebrum.


various aspects of the memory—information aboutthe person’s greeting, tone of voice, appearance, andlocation—are probably stored in different locationsin the cortex. But without the hippocampus, the in-formation would never get to these destinations. Aswe discuss in Chapter 8, this structure is also in-volved in the retrieval of information during recall.

The CerebrumAt this point in our tour, the largest part of thebrain still looms above us. It is the cauliflower-likecerebrum, where the higher forms of thinking takeplace. The complexity of the human brain’s cir-cuitry far exceeds that of any computer in existence,and much of its most complicated wiring is packedinto this structure. Compared to many other crea-tures, we humans may be ungainly, feeble, and thin-skinned, but our well-developed cerebrum enablesus to overcome these limitations and creativelycontrol our environment (and, some would say, tomess it up).

The cerebrum is divided into two separatehalves, or cerebral hemispheres, connected by alarge band of fibers called the corpus callosum. Ingeneral, the right hemisphere is in charge of the leftside of the body and the left hemisphere is incharge of the right side of the body. The two hemi-spheres also have somewhat different tasks and tal-ents, a phenomenon known as lateralization.

The Cerebral Cortex Working our way right upthrough the top of the brain, we find that the cere-brum is covered by several thin layers of denselypacked cells known collectively as the cerebral cor-tex. Cell bodies in the cortex, as in many other partsof the brain, produce a grayish tissue, hence theterm gray matter. In other parts of the brain (and inthe rest of the nervous system), long, myelin-covered axons prevail, providing the brain’s whitematter. Although the cortex is only about 3 mil-limeters (1/8 inch) thick, it contains almost three-fourths of all the cells in the human brain. Thecortex has many deep crevasses and wrinkles, whichenable it to contain its billions of neurons withoutrequiring us to have the heads of giants—heads thatwould be too big to permit us to be born. In othermammals, which have fewer neurons, the cortex isless crumpled; in rats, it is quite smooth.

Lobes of the Cortex In each cerebral hemi-sphere, deep fissures divide the cortex into four dis-tinct regions, or lobes (see Figure 4.11):

• The occipital lobes (from the Latin for “in backof the head”) are at the lower back part of the

brain. Among other things, they contain thevisual cortex, where visual signals are processed.Damage to the visual cortex can cause impairedvisual recognition or blindness.

• The parietal lobes (from the Latin for “pertain-ing to walls”) are at the top of the brain. Theycontain the somatosensory cortex, which receivesinformation about pressure, pain, touch, andtemperature from all over the body. The areas ofthe somatosensory cortex that receive signalsfrom the hands and the face are disproportion-ately large because these body parts are particu-larly sensitive.

• The temporal lobes (from the Latin for “pertain-ing to the temples”) are at the sides of the brain,just above the ears and behind the temples. Theyare involved in memory, perception, and emo-tion, and they contain the auditory cortex, whichprocesses sounds. An area of the left temporallobe known as Wernicke’s area is involved in lan-guage comprehension.

• The frontal lobes, as their name indicates, arelocated toward the front of the brain, just underthe skull in the area of the forehead. They containthe motor cortex, which issues orders to the 600muscles of the body that produce voluntary move-ment. In the left frontal lobe, a region known asBroca’s area handles speech production. Duringshort-term memory tasks, areas in the frontal

Motor cortex

Frontal lobe

Temporal lobe

Auditory cortex Visualcortex

Occipital lobe

Parietal lobe

Somatosensory cortex

FIGURE 4.11Lobes of the CerebrumDeep fissures divide the cortex of each cerebral hemi-sphere into four regions.

occipital [ahk-SIP-uh-tuhl] lobes Lobes at thelower back part of thebrain’s cerebral cortex;they contain areas thatreceive visual information.

frontal lobes Lobes atthe front of the brain’scerebral cortex; theycontain areas involved inshort-term memory,higher-order thinking,initiative, social judgment,and (in the left lobe, typi-cally) speech production.

temporal lobes Lobesat the sides of the brain’scerebral cortex; they con-tain areas involved inhearing, memory, percep-tion, emotion, and (in theleft lobe, typically) lan-guage comprehension.

parietal [puh-RYE-uh-tuhl] lobes Lobes at thetop of the brain’s cerebralcortex; they contain areasthat receive informationon pressure, pain, touch,and temperature.


lobes are especially active. The frontal lobes arealso involved in emotion and in the ability to makeplans, think creatively, and take initiative.

Because of their different functions, the lobesof the cerebral cortex tend to respond differentlywhen stimulated. If a surgeon applied electricalcurrent to your somatosensory cortex in the pari-etal lobes, you might feel a tingling in the skin or asense of being gently touched. If your visual cortexin the occipital lobes were electrically stimulated,you might report a flash of light or swirls of color.And, eerily, many areas of your cortex, when stimu-lated, would produce no obvious response or sensa-tion. These “silent” areas are sometimes called theassociation cortex because they are involved in highermental processes.

The Prefrontal Cortex Psychologists are espe-cially interested in the most forward part of thefrontal lobes, the prefrontal cortex. This area barelyexists in mice and rats and takes up only 3.5 percentof the cerebral cortex in cats and about 7 percent indogs, but it accounts for approximately one-third ofthe entire cortex in human beings. It is the most re-cently evolved part of our brains, and is associatedwith such complex abilities as reasoning, decisionmaking, and planning.

Scientists have long known that the frontallobes, and the prefrontal cortex in particular, mustalso have something to do with personality. Thefirst clue appeared in 1848, when a bizarre accidentdrove an inch-thick, 31⁄2-foot-long iron rod clearthrough the head of a young railroad worker namedPhineas Gage. As you can see in the photo, the rod(which is still on display at Harvard University,along with Gage’s skull) entered beneath the left eyeand exited through the top of the head, destroyingmuch of the prefrontal cortex (H. Damasio et al.,1994). Miraculously, Gage survived this traumaand, by most accounts, he retained the ability tospeak, think, and remember. But his friends com-plained that he was “no longer Gage.” In a sort ofJekyll-and-Hyde transformation, he had changedfrom a mild-mannered, friendly, efficient workerinto a foul-mouthed, ill-tempered, undependablelout who could not hold a steady job or stick to aplan. His employers had to let him go, and he wasreduced to exhibiting himself as a circus attraction.

There is some controversy about the details ofthis sad incident, but many other cases of braininjury, whether from stroke or trauma, support theconclusion that most scientists draw from theGage case: Parts of the frontal lobes are involved insocial judgment, rational decision making, andthe ability to set goals and to make and carry

On the left is the only known photo of Phineas Gage, taken after his recovery from an accident in which aniron rod penetrated his skull, altering his behavior and personality dramatically. The exact location of thebrain damage remained controversial for almost a century and a half, until Hanna and Antonio Damasio andtheir colleagues (1994) used measurements of Gage’s skull and MRIs of normal brains to plot possible tra-jectories of the rod. The reconstruction on the right shows that the damage occurred in an area of the pre-frontal cortex associated with emotional processing and rational decision making.


through plans. Like Gage, people with damage inthese areas sometimes mismanage their finances,lose their jobs, and abandon their friends.Interestingly, the mental deficits that characterizedamage to these areas are accompanied by a flat-tening out of emotion and feeling, whichsuggests that normal emotions are necessary foreveryday reasoning and the ability to learn frommistakes (Damasio, 1994, 2003; Levenson &Miller, 2007).

The frontal lobes also govern the ability to do aseries of tasks in the proper sequence and to stopdoing them at the proper time. The pioneeringSoviet psychologist Alexander Luria (1980) studiedmany cases in which damage to the frontal lobesdisrupted these abilities. One man Luria observedkept trying to light a match after it was already lit.Another planed a piece of wood in the hospitalcarpentry shop until it was gone and then went onto plane the workbench!

YOU are about to learn...• what would happen if the two cerebral hemispheres

could not communicate with each other.

• why researchers often refer to the left hemisphere as“dominant.”

• why “left-brainedness” and “right-brainedness” areexaggerations.

The Two Hemispheres of the BrainWe have seen that the cerebrum is divided into twohemispheres that control opposite sides of thebody. Although similar in structure, these hemi-spheres have somewhat separate talents, or areas ofspecialization.

Split Brains: A House DividedIn a normal brain, the two hemispheres communi-cate with one another across the corpus callosum,

the bundle of fibers that connects them. Whateverhappens in one side of the brain is instantly flashedto the other side. What would happen, though, ifthe two sides were cut off from one another?

In 1953, Ronald E. Myers and Roger W. Sperrytook the first step toward answering this question bysevering the corpus callosum in cats. They also cutparts of the nerves leading from the eyes to thebrain. Normally, each eye transmits messages toboth sides of the brain. (See Figure 4.12 on the nextpage.) After this procedure, a cat’s left eye sent in-formation only to the left hemisphere and its righteye sent information only to the right hemisphere.

At first, the cats did not seem to be affectedmuch by this drastic operation. But Myers andSperry showed that something profound had hap-pened. They trained the cats to perform tasks withone eye blindfolded; a cat might have to push apanel with a square on it to get food but ignore apanel with a circle. Then the researchers switchedthe blindfold to the cat’s other eye and tested theanimal again. Now the cats behaved as if they hadnever learned the trick. Apparently, one side of the

1.a2.c3.f4.b5.d6.e

Pause to see how your own brain is working by taking this quiz.

Match each description on the left with a term on the right.

1. Filters out irrelevant information

2. Known as the “gateway to memory”

3. Controls the autonomic nervous system; involved indrives associated with survival

4. Consists of two hemispheres

5. Wrinkled outer covering of the brain

6. Site of the motor cortex; associated with planning andtaking initiative

Quick Quiz

a. reticular activating system

b. cerebrum

c. hippocampus

d. cerebral cortex

e. frontal lobes

f. hypothalamus

Answers:


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brain did not know what the other side was doing;it was as if the animals had two minds in one body.Later studies confirmed this result with otherspecies, including monkeys (Sperry, 1964).

In all of the animal studies, ordinary behavior,such as eating and walking, remained normal. Inthe early 1960s, a team of surgeons decided to trycutting the corpus callosum in patients with debili-tating, uncontrollable epilepsy. In severe forms ofthis disease, disorganized electrical activity spreads

from an injured area to other parts of the brain.The surgeons reasoned that cutting the connectionbetween the two halves of the brain might stop thespread of electrical activity from one side to theother. The surgery was done, of course, for the sakeof the patients, who were desperate. But there was abonus for scientists, who would be able to find outwhat each cerebral hemisphere can do when it isquite literally cut off from the other.

The results of this split-brain surgery generallyproved successful. Seizures were reduced andsometimes disappeared completely. In their dailylives, split-brain patients did not seem much af-fected by the fact that the two hemispheres were in-communicado. Their personalities and intelligenceremained intact; they could walk, talk, and leadnormal lives. Apparently, connections in the undi-vided deeper parts of the brain kept body move-ments and other functions normal. But in a series ofingenious studies, Sperry and his colleagues (andlater, other researchers) showed that perceptionand memory had been affected, just as they hadbeen in the earlier animal research. Sperry won aNobel Prize for his work.

It was already known that the two hemispheresare not mirror images of each other. In most peo-ple, language is largely handled by the left hemi-sphere; thus, a person who suffers brain damagebecause of a stroke—a blockage in or rupture of ablood vessel in the brain—is much more likely tohave language problems if the damage is in the leftside than if it is in the right. Sperry and his col-leagues wanted to know how splitting the brainwould affect language and other abilities.

To understand this research, you must knowhow nerves connect the eyes to the brain. (Thehuman patients, unlike Myers and Sperry’s cats, didnot have these nerves cut.) If you look straightahead at the visual field in front of you, everythingin the left side of the scene goes to the right half ofyour brain, and everything in the right side of thescene goes to the left half of your brain. This is truefor both eyes. (Refer again to Figure 4.12.)

The procedure was to present informationonly to one or the other side of the patients’ brains.In one early study, the researchers took photo-graphs of different faces, cut them in two, andpasted different halves together (Levy, Trevarthen,& Sperry, 1972). The reconstructed photographswere then presented on slides (see Figure 4.13).The patients were told to stare at a dot in the mid-dle of the screen, so that half of the image fell to theleft of this point and half to the right. Each imagewas flashed so quickly that they had no time tomove their eyes. When the patients were asked to

Lefteye

Righteye

Optic nerve

Optic chiasm(crossover)

Relaycenters

Visual cortex

Speechproductionarea

Corpus callosum

LeftHemisphere

RightHemisphere

FIGURE 4.12Visual PathwaysEach cerebral hemisphere receives information from theeyes about the opposite side of the visual field. Thus, ifyou stare directly at the corner of a room, everything tothe left of the juncture is represented in your righthemisphere and vice versa. This is so because half theaxons in each optic nerve cross over (at the optic chiasm)to the opposite side of the brain. Normally, eachhemisphere immediately shares its information with theother one, but in split-brain patients, severing the corpuscallosum prevents such communication.


say what they had seen, they named the person inthe right part of the image (which would be the lit-tle boy in Figure 4.13). But when they were askedto point with their left hands to the face they hadseen, they chose the person in the left side of theimage (the mustached man in the figure). Further,they claimed they had noticed nothing unusualabout the original photographs! Each side of thebrain saw a different half-image and automaticallyfilled in the missing part. Neither side knew whatthe other side had seen.

Why did the patients name one side of the pic-ture but point to the other? Speech centers are usu-ally in the left hemisphere. When patientsresponded with speech, it was the left side of thebrain doing the talking. When patients pointedwith the left hand, which is controlled by the rightside of the brain, the right hemisphere was givingits version of what they had seen.

In another study, the researchers presentedslides of ordinary objects and then suddenly flasheda slide of a nude woman. Both sides of the brainwere amused, but because only the left side hasspeech, the two sides responded differently. Whenthe picture was flashed to one woman’s left hemi-sphere, she laughed and identified it as a nude.When it was flashed to her right hemisphere, shesaid nothing but began to chuckle. Asked what shewas laughing at, she said, “I don’t know ... nothing... oh—that funny machine.” The right hemispherecould not describe what it had seen, but it reactedemotionally just the same (Gazzaniga, 1967).

The Two Hemispheres: Allies or Opposites?The split-brain operation is still being performed,and split-brain patients continue to be studied, butresearch on left–right differences has also beendone with people whose brains are intact (Springer& Deutsch, 1998). Electrodes and brain scans havebeen used to measure activity in the left and righthemispheres while people perform different tasks.The results confirm that nearly all right-handedpeople and a majority of left-handers process lan-guage mainly in the left hemisphere. The left side isalso more active during some logical, symbolic, andsequential tasks, such as solving math problems andunderstanding technical material.

Because of its cognitive talents, manyresearchers refer to left-hemisphere dominance.They believe that the left hemisphere usually exertscontrol over the right hemisphere. Split-brain re-searcher Michael Gazzaniga (1983) once arguedthat without help from the left side, the right side’smental skills would probably be “vastly inferior tothe cognitive skills of a chimpanzee.” He and othersalso believe that a part of the left hemisphere isconstantly trying to explain actions and emotionsgenerated by brain parts whose workings are non-verbal and outside of awareness. As one neuropsy-chologist put it, the left hemisphere is the brain’sspin doctor (Broks, 2004).

Other researchers, including Sperry (1982),have rushed to the right hemisphere’s defense. The

Simulate

“Look at the center of the slide.”

“Point to the person you saw.” Left hemisphere Right hemisphere

(a)

(b) (c)

FIGURE 4.13Divided ViewSplit-brain patients wereshown composite photo-graphs (a) and were thenasked to pick out the facethey had seen from aseries of intact photo-graphs (b). They said theyhad seen the face on theright side of the compos-ite, yet they pointed withtheir left hands to the facethat had been on the left.Because the two cerebralhemispheres could notcommunicate, the verballeft hemisphere was awareof only the right half ofthe picture, and therelatively mute righthemisphere was aware ofonly the left half (c).

SimulateSplit-BrainExperiments onmypsychlab.com


right side, they point out, is no dummy. It is supe-rior in problems requiring spatial–visual ability, theability you use to read a map or follow a dress pat-tern, and it excels in facial recognition and the abil-ity to read facial expressions. It is active during thecreation and appreciation of art and music. It rec-ognizes nonverbal sounds, such as a dog’s barking.The right brain also has some language ability.Typically, it can read a word briefly flashed to it and

can understand an experimenter’s instructions. In afew split-brain patients, right-brain language abilityhas been well developed, showing that individualvariation exists in brain lateralization.

Some researchers have also credited the righthemisphere with having a cognitive style that is intu-itive and holistic, in contrast to the left hemisphere’smore rational and analytic mode. This idea has beenoversold by books and programs that promise tomake people more cre-ative by making themmore “right-brained.”But the right hemi-sphere is not always ahero: It contains frontal lobe regions that process fearand sadness, emotions that often cause us to with-draw from others. Further, the differences betweenthe two hemispheres are relative, not absolute—amatter of degree. In most activities, the two sidescooperate naturally, with each making a valuable con-tribution. Be cautious, then, about thinking of thetwo sides as two “minds.” As Sperry (1982) himselfnoted long ago, “The left–right dichotomy . . . is anidea with which it is very easy to run wild.”

Get Involved! TAP, TAP, TAP

Have a right-handed friend tap on a paper with a pencil held in the right hand for one minute. Then havethe person do the same with the left hand, using a fresh sheet of paper. Finally, repeat the procedure,having the person talk at the same time as tapping. For most people, talking will decrease the rate oftapping—but more for the right hand than for the left, probably because both activities involve the samehemisphere (the left one), and there is competition between them. Left-handed people vary more in termsof which hemisphere is dominant for language, so the results for them will be more varied.

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1.c, d2.One possible answer: Human beings like to make sense of the world, and one easy way to do that is to divide humanity intoopposing categories. This kind of either–or thinking can lead to the conclusion that fixing up one brain hemisphere (e.g., making “left-brained” types more “right-brained”) will make individuals happier and the world a better place. If only it were that simple!

Use as many parts of your brain as necessary to answer these questions.

1. Bearing in mind that both sides of the brain are involved in most activities, identify which of the followingis (are) more closely associated with the left hemisphere: (a) enjoying a musical recording, (b) wiggling theleft big toe, (c) giving a speech in class, (d) balancing a checkbook, (e) recognizing a long-lost friend.

2. Thousands of people have taken courses and bought tapes that promise to develop the creativity and intu-ition of their right hemispheres. What characteristics of human thought might explain the eagerness ofsome people to glorify “right-brainedness” and disparage “left-brainedness” (or vice versa)?

Answers:

Thinking Criticallyabout Right Brain/Left Brain Theories

Quick QuizReview onmypsychlab.com

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YOU are about to learn...• why some brain researchers think a unified “self” is

only an illusion.

• findings and fallacies about sex differences in thebrain.

Two Stubborn Issues in Brain ResearchIf you have mastered the definitions and descrip-tions in this chapter, you are prepared to follownews of advances in neuropsychology. Yet manyquestions remain about how the brain works, andwe will end this chapter with two of them.

Where Is the Self?When you say, “I am feeling unhappy,” your amyg-dala, your serotonin receptors, your endorphins,and all sorts of other brain parts and processes areactive, but who, exactly, is the “I” doing the feeling?

When you say, “Mymind is playing tricks onme,” who is the “me”watching your mindplay those tricks, and

who is it that’s being tricked? Isn’t the self observ-ing itself a little like a finger pointing at its own tip?Because the brain is the site of self-awareness, peo-ple even disagree about what language to use whenreferring to it. If we say that your brain storesevents or registers emotions, we imply a separate“you” that is “using” that brain. But if we leave“you” out of the picture and just say the brain doesthese things, we risk ignoring the motives, person-ality traits, and social conditions that powerfullyaffect what people do—what you do.

Most religions resolve the problem by teachingthat an immortal self or soul exists entirely apartfrom the mortal brain, a doctrine known as dualism.But modern brain scientists usually consider mindto be a matter of matter. They may have religiousconvictions about a soul or a spiritual response tothe awesome complexity and interconnectedness ofnature, but most assume that what we call “mind,”“consciousness,” “self-awareness,” or “subjectiveexperience” can be explained in physical terms as aproduct of the cerebral cortex.

Our conscious sense of a unified self may evenbe an illusion. Neurologist Richard Restak (1994)notes that many of our actions and choices occurwithout any direction by a central, conscious self.Cognitive scientist Daniel Dennett (1991) suggests

that the brain or mind consists of independent brainparts that deal with different aspects of thought andperception, constantly conferring with each otherand revising their versions of reality. And MichaelGazzaniga proposes that the brain is organized as aloose confederation of independent modules, ormental systems, all working in parallel, with most ofthese modules operating outside of conscious aware-ness. One verbal module, an “interpreter” (usually inthe left hemisphere), is constantly explaining the ac-tions, moods, and thoughts produced by the othermodules (Gazzaniga, 1998; Roser & Gazzaniga,2004). The result is the sense of a unified self.

The idea that the self is an illusion echoes theteachings of many Eastern spiritual traditions, suchas Buddhism. Buddhism teaches that the self is not aunified, tangible thing but rather a collection ofthoughts, perceptions, concepts, and feelings thatshift and change from moment to moment. To Bud-dhists, the unity and the permanence of the self are amirage. Such notions are contrary, of course, towhat most people in the West, including psycholo-gists, have always believed about their “selves.”

Whether or not the self is an illusion, we allhave a sense of self; otherwise, there would be noneed for the words I and me. Yet even in these daysof modern technology, and despite much debateamong scientists and philosophers, the neuralcircuits responsible for our sense of self remainhazy. How is the inner life of the mind, our sense ofsubjective experience, linked to the physicalprocesses of the brain? Some neuroscientists argue

Thinking Criticallyabout the Brain andthe Self


that specific groups of neurons form unique neu-ronal coalitions for seeing red, seeing our grand-mother, or feeling joy (Koch, 2004). Othersemphasize the transient synchronization of millionsof neurons across wide areas of the brain, synchro-nization that changes from moment to moment(Greenfield & Collins, 2005). But in either case,how does that brain activity cause a person’s joy onseeing her adored grandmother in a new red hat?We don’t know. Nor do we understand why somepatients with severe degeneration of the frontallobes have unimpaired memories and language yetundergo a change in self comparable to PhineasGage’s transformation (Levenson & Miller, 2007).These patients can walk, talk, and function, and yettheir families and friends don’t know them; they areno longer “themselves.”

Psychologists, neuroscientists, cognitive scien-tists, and philosophers all hope to learn more abouthow our brains and nervous systems give rise to theself. In the meantime, what do you think about theexistence and location of your own “self” . . . andwho, by the way, is doing the thinking?

Are There “His” and “Hers”Brains?A second stubborn issue for brain scientists con-cerns sex differences in the brain. On this issue,either–or thinking is a great temptation. Because ofthe centuries of prejudice against women and alegacy of biased research on gender differences,some scientists and laypeople do not even want toconsider the possibility that the brains of women

and men might differ, on average, in some ways.Others go overboard in the opposite direction, con-vinced that most, if not all, differences between thesexes are in fact “all in the brain.” Every year, morebooks arrive claiming that the “female brain” andthe “male brain” are as unlike as tomatoes and arti-chokes. To evaluate this issue intelligently, we needto ask two separate questions: Do the brains of malesand females differ? And if so, what, if anything, dothe differences have to do with men’s and women’sbehavior, abilities, or ways of solving problems?

Let’s consider the first question. Many anatom-ical and biochemical sex differences have been foundin animal brains, and advances in technology haverevealed some intriguing differences in humanbrains as well. In a study of nine autopsied brains,researchers found that the women’s brains had anaverage of 11 percent more cells in areas of thecortex associated with the processing of auditoryinformation; in fact, all of the women had more ofthese cells than did any of the men (Witelson,Glazer, & Kigar, 1994). Brain scans show that partsof the frontal lobes and the limbic system are largerin women, relative to the overall size of their brains,whereas parts of the parietal cortex and the amyg-dala are larger in men (Goldstein et al., 2001; Guret al., 2002). Women also have more cortical folds inthe frontal and parietal lobes (Luders et al., 2004).

Researchers are also using brain scans to searchfor average sex differences in brain activity whenpeople work on particular tasks. In one study, 19men and 19 women were asked to say whether pairsof nonsense words rhymed, a task that requiredthem to process and compare sounds. MRI scansshowed that in both sexes an area at the front of theleft hemisphere was activated. But in 11 of thewomen and none of the men, the corresponding areain the right hemisphere was also active (Shaywitzet al., 1995). In another MRI study, 10 men and10 women listened to a John Grisham thriller beingread aloud. Men and women alike showed activityin the left temporal lobe, but women also showedsome activity in the right temporal lobe, as you cansee in Figure 4.14 (Phillips et al., 2001). Thesefindings, along with many others, provide evidencefor a sex difference in lateralization: For some typesof tasks, especially those involving language, menseem to rely more heavily on one side of the brainwhereas women tend to use both sides.

Thus, the answer to our first question is thatyes, average sex differences in the brain do exist.But we are still left with our second question: Whatdo the differences mean for the behavior or personalitytraits of men and women in ordinary life? Somewriters have been quick to assume that brain differ-

Cartoons like this one make most people laugh because men and women do differ, onaverage, in things like “love of shopping” and “power-tool adoration.” But what does theresearch show about sex differences in the brain? And what do they mean for howpeople behave in real life?


ences explain, among other things, women’s al-legedly superior intuition, women’s love of talkingabout feelings and men’s love of talking about

sports, women’s greaterverbal ability, men’sedge in math ability,why women can’t readmaps, and why men

won’t ask for directions when they’re lost. Thereare at least three problems with such conclusions:

1Many supposed gender differences (in intu-ition, abilities, and so forth) are stereotypes,

which are misleading because the overlap betweenthe sexes is usually greater than the difference be-tween them. As we saw in Chapter 1, even whengender differences are statistically significant, theyare often quite small in practical terms. Some sup-posed differences, on closer inspection, even disap-pear. For instance, are women more talkative thanmen, as many pop-psych books about the sexes as-sert? To test this assumption, psychologists wiredup a sample of men and women with voicerecorders that tracked their conversations whilethey went about their daily lives. There was no sig-nificant gender difference in the number of wordsspoken: Both sexes used about 16,000 words perday on average, with large individual differencesamong the participants (Mehl et al., 2007). Like-wise, the difference between boys and girls in mathscores is shrinking and in some studies is approach-ing zero (Else-Quest, Hyde, & Linn, 2010).

2A brain difference does not necessarily pro-duce a difference in behavior or performance.

In many studies, males and females have shown dif-ferent patterns of brain activity while they are doingsomething or while an ability is being tested, butthey have not differed in the behavior or ability inquestion—which, after all, is presumably the thingto be explained. In the rhyme-judgment task, bothsexes did equally well, despite the differences intheir MRIs. Another research team used MRI scansto examine the brains of men and women who hadequivalent IQ scores. Women’s brains had morewhite-matter areas related to intelligence, whereasmen’s brains had more gray-matter areas related tointelligence; there were some other differences aswell (Haier et al., 2005). The researchers concludedthat brains may be organized differently yet producethe same intellectual abilities.

3Sex differences in the brain could be the resultrather than the cause of behavioral differ-

ences. Culture and experience are constantlysculpting the circuitry of the brain, affecting the

way brains are organized and how they function.Women and men, of course, often have differentexperiences in childhood and throughout theirlives. Thus, in commenting on the study that hadpeople listen to a John Grisham novel, one of theresearchers noted: “We don’t know if the [sex dif-ference we found] is because of the way we’reraised, or if it’s hard-wired in the brain” (quoted inHotz, 2000).

In sum, the answer to our second question,whether anatomical differences are linked to behav-ior and abilities, is: It’s uncertain. Animal studieshave provided tantalizing clues, suggesting that sexdifferences in the brain influence reactions to acuteor chronic stress, the likelihood of suffering depres-sion and attention deficit/hyperactivity disorder,memory for emotional events, strategies for navi-gating around the environment, and other aspectsof behavior (Cahill, 2005; Becker et al., 2008). Butwe simply do not yet know which of these findingsare important for how human males and femalesmanage their everyday lives—their work, their rela-tionships, their families. It is good to keep an openmind about new findings on sex differences in thebrain, but because the practical significance of thesefindings (if any) is not yet clear, it is also importantnot to oversimplify, as one popular book after an-other keeps doing. The topic of sex differences inthe brain is a sexy one, and research in this area caneasily be exaggerated and misused.

FIGURE 4.14Gender and the BrainWhen women and men listened to a John Grisham thriller read aloud, they showedactivity in the left temporal lobe, but women also showed some activity in the righttemporal lobe (Phillips et al., 2001). (Because of the orientation of these MRI images,the left hemisphere is seen on the right and vice versa.) Along with other evidence,these results suggest a sex difference in lateralization on tasks involving language.

Thinking Criticallyabout Sex Differencesin the Brain

Simulate

SimulatePhysiologicalBases ofBehavioralProblems onmypsychlab.com


1.independent modules or mental systems2.The sample size was very small; have the results been replicated? Were the sex differ-ences more impressive than the similarities? Might eating chocolate affect chocolate receptors rather than the other way around? Mostimportant, was the number of receptors actually related to the amount of chocolate eaten by the brains’ owners in real life?

Men and women alike have brains that can answer these questions.

1. Many brain researchers and cognitive scientists believe that the self is not a unified “thing” but a collec-tion of ____________.

2. A new study reports that in a sample of 11 brains, 4 of the 6 women’s brains but only 2 of the 5 men’sbrains had multiple chocolate receptors. (Note: We made this up; there’s no such thing as a chocolatereceptor!) The researchers conclude that their findings explain why so many women are addicted tochocolate. What concerns should a critical thinker have about this study?

Answers:

Quick Quiz

R E V I S I T E D

Now that you know more about the workings ofthe brain, let’s return to the opening story ofthe patients who were in vegetative or mini-

mally conscious states but who appeared to have somebrain function. Political and religious debates continueover the rights of incapacitated people, the meaning of“death by natural causes,” and when life should end if aperson has left no written instructions. We cannotresolve these debates here, but the information in thischapter, and an increased understanding of the brain,can help us to separate what we might wish to be trueabout a patient’s mental abilities from what really is true.

Consider the tragic case of Terri Schiavo, whoseparents and husband fought over the decision to termi-nate her life. She had been in a persistent vegetativestate for 15 years, after a heart attack cut off oxygen toher brain. A few years before her death, a scan of Schi-avo’s brain showed widespread destruction of braincells in the cerebral cortex and their replacement byfluid. Yet her parents were convinced that she couldrecognize them and respond to questions. To a lovingand desperately hopeful family, these intermittent, rarereactions seemed like signs of recognition and mentalfunctioning. What they failed to accept is that activityin the brain stem can produce reflexive responsessuch as facial expressions and eye movements, withoutany awareness or thought on the patient’s part andwithout any connection to events in the environment.

Eventually, a judge gaveTerri’s husband permis-sion to have her feedingtube removed, and shedied peacefully soonthereafter.

What, then, about the man who responded toyes–no questions by imagining scenarios that produced

Psychology in the News

The scan on the left, which was made three years beforeTerri Schiavo’s death, shows severe atrophy in her brain.The dark areas are massively enlarged ventricles filledwith cerebral spinal fluid, which had by then replacedmuch of her cerebral cortex. On the right is a normalbrain, showing typical small ventricles.


Study and

Traces of Consciousness Foundin Some Patients Diagnosed as“Vegetative”LIEGE, BELGIUM, February 4, 2010. A 29-year-oldman thought to have been in a persistent vegetativestate for five years following a car accident has shownsigns of brain activity in response to questions fromdoctors. Most patients who are in a vegetative state canopen and move their eyes and may make sounds andfacial expressions, but they have no conscious aware-ness of themselves or their environment and cannotthink or reason.

The man is one of 54 patients with severe braindamage, resulting in their being either in a vegetative orminimally conscious state, who are being studied by aninternational team of scientists in England andBelgium. Researchers prompted them to imagine them-selves playing tennis or walking through the house theygrew up in, as their brains were being scanned by func-tional magnetic resonance imaging (MRI). Five of the54 were able to intentionally modulate their brain activ-ity in response to these prompts, just as healthy peoplein a control group could. The researchers then in-structed these five patients to respond to yes–no ques-tions by using one type of mental imagery (eitherplaying tennis or walking through the house) for “yes”and the other for “no.” Only the man who had been in-jured in the car accident was able to do this success-fully. He responded accurately to simple questions,such as whether his father’s name was Paul (yes) orAlexander (no), and whether he had ever been to theUnited States. Yet, at a bedside evaluation by a skilledclinical team, he showed no consciousness or ability tocommunicate.

Experts continue to debate just what these findingsmean for a patient’s state of cognition and conscious-ness. In 2009, Rom Houben, another victim of a carcrash who apparently was unconscious for 23 years,

Psychology in the Newsmade headlines when neurological tests indicated thathe too had some possible awareness, and a brain scanrevealed nearly normal activity in his brain. Therapistsprovided Houben with a computer touch screen thatseemed to allow him to communicate by spelling outwords. But skeptics pointed out that all of Houben’smessages were typed with the help of an aide who sup-ported and guided his hand. Scientific research has dis-credited such “facilitated communication” and hasfound that the typed messages come from the facilita-tor, not the patient. After watching a video of Houbensupposedly communicating as a facilitator guided hishand, bioethics expert Arthur Caplan commented, “Thatis Ouija board stuff.”

Nonetheless, these studies suggest that, in rarecases, patients with brain injury may have a greater de-gree of consciousness than previously believed possible.“With further development,” the researchers conclude,“this technique could be used by some patients toexpress their thoughts, control their environment, andincrease their quality of life.”


different patterns of activity in his brain? His brain re-sponses suggest that he does have some awareness. His case holds out the tantalizing possibility that fMRI technology will eventually help doctors distinguishwith greater certainty among conscious, minimally conscious, and persistent vegetative states (Monti et al.,2010).

Yet many challenges remain, and at present wemust tolerate uncertainty about the implications of thisresearch. Consciousness comes in many forms, includ-ing intense alertness, as when you are faced with dan-ger or an exam; a loss of self-awareness, as when youare immersed in a good book or movie; and the floatingstate between sleep and wakefulness. Brain scansalone cannot necessarily reveal what form of conscious-ness, if any, someone with brain damage due to acci-dent or disease is experiencing. Evidence of corticalactivity is not evidence of an internal stream of con-scious thought (Ropper, 2010). As we saw in this chap-ter, neural correlates of consciousness remain murkyand, besides, a brain scan does not tell us exactly whata person is thinking or understands. As we also saw, thebrain needs stimulation to survive. We do not yet knowhow years of what amounts to solitary confinement mayaffect a patient’s brain.

The study of our most miraculous organ, the brain,can help us to better understand the effects of braindamage, and it inspires us to hope for the benefits thatfuture discoveries will bring. But it also teaches us to becautious and skeptical about the medical and ethical im-plications of dramatic findings that make the news.Heart-warming reports that Rom Houben, also describedin our opening story, had communicated with his motherand his neurologist through “facilitated communication”flashed around the world before independent scientistsdemonstrated unmistakably that Houben’s communica-tions were coming from the facilitators, not Houben.When the researchers shielded the facilitator’s eyes fromthe keyboard, for example, Houben began typing gibber-ish (Boudry, Termote, & Betz, 2010).

The study of the brain provides valuable insightsinto the abilities those of us with healthy brains take forgranted every day. However, keep in mind that analyz-ing a human being in terms of physiology alone is likeanalyzing the Taj Mahal solely in terms of the materialsthat were used to build it. Even if we could monitorevery cell and circuit of the brain, we would still needto understand the circumstances, thoughts, and cul-tural rules that affect whether we are gripped by hatred,consumed by grief, lifted by love, or transported by joy.

Cosmetic Neurology: Tinkering with the Brain

Taking Psychology with You

Should healthy people be permitted, evenencouraged, to take “brain boosters” or“neuroenhancers”—drugs that will sharpenconcentration and memory? What about a pillthat could erase a traumatic memory? If hav-ing cosmetic surgery can change parts of yourbody that you don’t like, what’s wrong withallowing cosmetic neurology to tinker withparts of your brain that you don’t like?

For centuries, people have been seekingways to stimulate their brains to work more ef-ficiently, with caffeine being an especiallypopular drug of choice. No one objects to re-search showing that diet and exercise can im-prove learning and memory. No one has aproblem with the finding that omega-3s,found in some kinds of fish, may help protect

against age-related mental decline (Beydounet al., 2007; van Gelder et al., 2007). Butwhen it comes to medications that increasealertness or appear to enhance memory andother cognitive functions, it’s another kettle offish oil, so to speak.

What questions should critical thinkersask, and what kind of evidence would beneeded, to make wise decisions about usingsuch medications? A new interdisciplinaryspecialty, neuroethics, has been formed to ad-dress the many legal, ethical, and scientificquestions raised by brain research, includingthose raised by the development of neuroen-hancing drugs (Gazzaniga, 2005).

Much of the buzz has focused on Provigil(modafinil), a drug approved for treating

narcolepsy and other sleep disorders, and Ri-talin and Adderall, approved for attentiondeficit disorders. Many students, pilots, busi-ness people, and jet-lagged travelers are tak-ing one or another of these drugs, eitherobtaining them illegally from friends or the In-ternet or getting their own prescriptions. Nat-urally, most of these users claim the drugshelp them, and one review of the literatureconcluded that Provigil does improve memoryand may have other cognitive benefits(Minzenberg & Carter, 2008).

Yet, as is unfortunately true of just aboutall medications, there is a down side thatrarely makes news, especially with new drugsthat promise easy fixes to old human prob-lems and have not yet been tested over many

Summary

• Neuropsychologists and other scientists study thebrain because it is the bedrock of consciousness, per-ception, memory, and emotion.

The Nervous System: A Basic Blueprint• The function of the nervous system is to gather andprocess information, produce responses to stimuli, andcoordinate the workings of different cells. Scientists di-vide it into the central nervous system (CNS) and theperipheral nervous system (PNS). The CNS, which in-cludes the brain and spinal cord, receives, processes,

interprets, and stores information and sends out mes-sages destined for muscles, glands, and organs. ThePNS transmits information to and from the CNS by wayof sensory and motor nerves.

• The peripheral nervous system consists of the somaticnervous system, which permits sensation and voluntaryactions, and the autonomic nervous system, which regu-lates blood vessels, glands, and internal (visceral) or-gans. The autonomic system usually functions withoutconscious control. The autonomic nervous system is fur-ther divided into the sympathetic nervous system, whichmobilizes the body for action, and the parasympatheticnervous system, which conserves energy.


years. Adderall, like all amphetamines, cancause nervousness, headaches, sleepless-ness, allergic rashes, and loss of appetite,and, as the label says, it has “a high potentialfor abuse.” Provigil, too, is habit-forming. An-other memory-enhancing drug being studiedtargets a type of glutamate receptor in thebrain. The drug apparently improves short-term memory nicely—at the price of detract-ing from long-term memories (Talbot, 2009).

Even when a drug is benign for most of itsusers, it may have some surprising and unex-pected consequences. For example, cogni-tive psychologists have found that the betterable people are to focus and concentrate ona task—the reason for taking stimulants inthe first place—the less creative they oftenare. Creativity, after all, comes from beingable to let our minds roam freely, at leisure.One neurologist therefore worries that theroutine use of mind-enhancing drugs amongstudents could create “a generation of veryfocussed accountants” (quoted in Talbot,2009).

Some bioethicists and neuroscientists feelthat cognitive enhancement is perfectly fine,because it is human nature for people to try toimprove themselves and society will benefitwhen people learn faster and remember more.After all, we use eyeglasses to improve visionand hearing aids to improve hearing; why notuse pills to improve our memories and othermental skills? One team of scientists has ar-gued that improving brain function with pillsis no more objectionable than eating right orgetting a good night’s sleep. They wrote, “In a

world in which human workspans and lifespans are increasing, cognitive enhancementtools . . . will be increasingly useful for im-proved quality of life and extended work pro-ductivity, as well as to stave off normal andpathological age-related cognitive declines”(Greely et al., 2008).

Other scientists and social critics, how-ever, consider cosmetic neurology to be aform of cheating that will give those who canafford the drugs an unfair advantage and in-crease socioeconomic inequalities. They thinkthe issue is no different from the (prohibited)use of performance-enhancing steroids in ath-letics. Yes, people wear glasses and hearingaids, but glasses and hearing aids do not haveside effects or interact negatively with othertreatments. Many neuroethicists also worrythat ambitious parents will start giving thesemedications to their children to try to boostthe child’s academic performance, despitepossible hazards for the child’s developingbrain. One reporter covering the pros andcons of neuroenhancers concluded, “All thismay be leading to the kind of society I’m notsure I want to live in: a society where we’reeven more overworked and driven by technol-ogy than we already are, and where we have totake drugs to keep up” (Talbot, 2009).

How about using drugs not to enhancememory but to erase it, especially memoriesof sorrowful and traumatic events? By alteringthe biochemistry of the brain in mice or rats,or using a toxin to kill targeted cells,researchers have been able to wipe out theanimals’ memories of a learned shock, their

ability to recall a learned fear, or their memoryof an object previously seen, while leavingother memories intact (Cao et al., 2008; Hanet al., 2009; Serrano et al., 2008). If theseresults eventually apply to human beings,what, again, are the implications?

Some victims of sexual or physical abuse,wartime atrocities, or a sudden horrifyingdisaster might welcome the chance to berid of their disturbing memories. But could a“delete” button for the brain be used toooften, changing the storehouse of memoriesthat make us who we are? Could memoryerasure be misused by unscrupulous govern-ments to eliminate dissent, as George Orwellfamously predicted it would in his great novel1984? Should we wish to erase memoriesthat evoke embarrassment or guilt, emotionsthat are unpleasant yet enable us to developand retain a sense of morality and learn fromour mistakes? And would we come to regretthe obliteration of a part of our lives that con-tributed to creating the person we are now?Such concerns may be the reason that mostpeople, when asked if they would take a pillto eradicate a painful memory, respond loudlyand clearly: No, thanks (Berkowitz et al.,2008).

In contrast, many people might say “Yes,please” to brain-enhancing drugs. But beforethey do, they will need to think critically—byseparating anecdotes from data, real dangersfrom false alarms, and immediate benefitsfrom long-term risks. What is to be gainedfrom neuroenhancers, and what might belost?

Listen to an audio file of your chapter on mypsychlab.com


Communicationin the Nervous System• Neurons are the basic units of the nervous system.They are held in place by glial cells, which nourish, in-sulate, and protect them, and enable them to functionproperly. Each neuron consists of dendrites, a cellbody, and an axon. In the peripheral nervous system,axons (and sometimes dendrites) are collected togetherin bundles called nerves. Many axons are insulated by amyelin sheath that speeds up the conduction of neuralimpulses and prevents signals in adjacent cells from in-terfering with one another.

• Research has disproven two old assumptions: thatneurons in the human central nervous system cannot beinduced to regenerate and that no new neurons formafter early infancy. In the laboratory, neurons have beeninduced to regenerate. And scientists have learned thatstem cells in brain areas associated with learning andmemory continue to divide and mature throughout adult-hood, giving rise to new neurons. A stimulating environ-ment seems to enhance this process of neurogenesis.

• Communication between two neurons occurs at thesynapse. Many synapses have not yet formed at birth.During development, axons and dendrites continue togrow as a result of both physical maturation and experi-ence with the world, and throughout life, new learningresults in new synaptic connections in the brain. Thus,the brain’s circuits are not fixed and immutable but arecontinually changing in response to information, chal-lenges, and changes in the environment, a phenomenonknown as plasticity. In some people who have been blindfrom an early age, brain regions usually devoted to visionare activated by sound, a dramatic example of plasticity.

• When a wave of electrical voltage (action potential)reaches the end of a transmitting axon, neurotransmittermolecules are released into the synaptic cleft. Whenthese molecules bind to receptor sites on the receivingneuron, that neuron becomes either more likely to fire orless so. The message that reaches a final destination de-pends on how frequently particular neurons are firing,how many are firing, what types are firing, their degreeof synchrony, and where they are located.

• Neurotransmitters play a critical role in mood, mem-ory, and psychological well-being. Abnormal levels ofneurotransmitters have been implicated in various emo-tional and physical disorders, such as Alzheimer’s dis-ease and Parkinson’s disease.

• Endorphins, which act primarily by modifying the ac-tion of neurotransmitters, reduce pain and promotepleasure. Endorphin levels seem to shoot up when ananimal or person is afraid or is under stress. Endorphinshave also been linked to the pleasures of social contact.

• Hormones, produced mainly by the endocrine glands,affect and are affected by the nervous system. Psycholo-gists are especially interested in melatonin, which

promotes sleep and helps regulate bodily rhythms;oxytocin and vasopressin, which play a role in attach-ment and trust; adrenal hormones such as epinephrineand norepinephrine, which are involved in emotions andstress; and the sex hormones, which are involved in thephysical changes of puberty, the menstrual cycle(estrogens and progesterone), sexual arousal(testosterone), and some nonreproductive functions—in-cluding, some researchers believe, mental functioning.

Mapping the Brain• Researchers study the brain by observing patientswith brain damage; by using the lesion method with an-imals; and by using such techniques aselectroencephalograms (EEGs), transcranial magneticstimulation (TMS), positron emission tomography (PETscans), magnetic resonance imaging (MRI), andfunctional MRI (fMRI).

• Brain scans reveal which parts of the brain are ac-tive during different tasks but do not tell us preciselywhat is happening, either physically or mentally, dur-ing the task. They do not reveal discrete “centers” fora particular function, and they must be interpretedcautiously.

A Tour through the Brain• All modern brain theories assume localization offunction, although a particular area may have severalfunctions and many areas are likely to be involved inany particular activity.

• In the lower part of the brain, in the brain stem, themedulla controls automatic functions such as heartbeatand breathing, and the pons is involved in sleeping,waking, and dreaming. The reticular activating system(RAS) screens incoming information and is responsiblefor alertness. The cerebellum contributes to balanceand muscle coordination, and may also play a role insome higher mental operations.

• The thalamus directs sensory messages to appropri-ate higher centers. The hypothalamus is involved inemotion and in drives associated with survival. It alsocontrols the operations of the autonomic nervous sys-tem, and sends out chemicals that tell the pituitarygland when to “talk” to other endocrine glands. Alongwith other structures, the hypothalamus has tradition-ally been considered part of the limbic system, which isinvolved in emotions that we share with other animals.However, the usefulness of speaking of the limbic sys-tem as an integrated set of structures is now in dispute.

• The amygdala is responsible for evaluating sensoryinformation and quickly determining its emotional im-portance, and for the initial decision to approach orwithdraw from a person or situation. It is also involvedin forming and retrieving emotional memories. The


hippocampus has been called the “gateway to memory”because it plays a critical role in the formation of long-term memories for facts and events. It is also involvedin other aspects of memory. Like the hypothalamus,these two structures have traditionally been classifiedas “limbic.”

• Much of the brain’s circuitry is packed into thecerebrum, which is divided into two hemispheres and iscovered by thin layers of cells known collectively as thecerebral cortex. The occipital, parietal, temporal, andfrontal lobes of the cortex have specialized (butpartially overlapping) functions. The association cortexappears to be responsible for higher mental processes.The frontal lobes, particularly areas in the prefrontalcortex, are involved in social judgment, the making andcarrying out of plans, and decision making.

The Two Hemispheres of the Brain• Studies of split-brain patients, who have had thecorpus callosum cut, show that the two cerebral hemi-spheres have somewhat different talents. In most peo-ple, language is processed mainly in the lefthemisphere, which generally is specialized for logical,symbolic, and sequential tasks. The right hemisphere isassociated with spatial–visual tasks, facial recognition,and the creation and appreciation of art and music. Inmost mental activities, however, the two hemispherescooperate as partners, with each making a valuablecontribution.

Two Stubborn Issues in Brain Research• One of the oldest questions in the study of the brainis where the “self” resides. Many brain researchers andcognitive scientists believe that a unified self may be

something of an illusion. Some argue that the brainoperates as a collection of independent modules ormental systems, perhaps with one of them functioningas an “interpreter.” But much remains to be learnedabout the relationship between the brain and the mind.

• Brain scans and other techniques have revealedsome differences in the brains of males and femalesand in lateralization during tasks involving language(with females more likely to use both hemispheres).Controversy exists, however, about what such differ-ences mean in real life. Speculation has often focusedon behavioral or cognitive differences that are smalland insignificant. Biological differences do not neces-sarily explain behavioral ones, and sex differences inexperience could affect brain organization rather thanthe other way around.

Psychology in the News,Revisited• Knowledge about the brain can help physicians as-sess the consequences of severe brain damage and im-prove their methods of diagnosing patients who are inpersistent vegetative states, minimally conscious, orconscious. Consciousness itself comes in many differ-ent forms, and brain scans to date do not tell us exactlywhat a person is thinking or understands. The study ofthe brain can help us to better understand the effectsof brain damage, and it also teaches us to be hopefulbut cautious about the medical and ethical implica-tions of dramatic findings that make the news.

Taking Psychology with You• Scholars in the new field of neuroethics are address-ing the implications of “cosmetic neurology,” espe-cially questions raised by the development of drugsthat are “neuroenhancers.”

central nervous system 114

spinal cord 114

spinal reflexes 115

peripheral nervous system 115

sensory nerves 115

motor nerves 115

somatic nervous system 115

autonomic nervous system 115

sympathetic nervous system 115

parasympathetic nervous system 115

neuron 117

glia 117

dendrites 117

cell body 117

axon 117

axon terminals 118

myelin sheath 118

nodes 118

nerves 118

neurogenesis 118

stem cells 118

synaptic cleft 119

synapse 119

action potential 119

synaptic vesicles 119

neurotransmitter 119

receptor sites 119

plasticity 120

endorphins 122

hormones 122

endocrine glands 122

melatonin 123

oxytocin 123

Key Terms


vasopressin 123

adrenal hormones 123

cortisol 123

epinephrine and norepinephrine 123

sex hormones (androgens, estrogens,progesterone) 123

lesion method 124

electrode 124

electroencephalogram (EEG) 124

transcranial magnetic stimulation(TMS) 124

PET scan (positron-emissiontomography) 125

MRI (magnetic resonance imaging) 125

functional MRI (fMRI) 125

localization of function 126

brain stem 126

pons 126

medulla 126

reticular activating system (RAS) 127

cerebellum 127

thalamus 127

olfactory bulb 127

hypothalamus 127

pituitary gland 128

limbic system 128

amygdala 128

hippocampus 128

cerebrum 129

cerebral hemispheres 129

corpus callosum 129

lateralization 129

cerebral cortex 129

occipital lobes 129

visual cortex 129

parietal lobes 129

somatosensory cortex 129

temporal lobes 129

auditory cortex 129

Wernicke’s area 129

frontal lobes 129

motor cortex 129

Broca’s area 129

association cortex 130

prefrontal cortex 130

split-brain surgery 132

visual field 133

(hemispheric) dominance 133

neuroethics 139

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Neuropsychologists study the brain and the rest of the nervoussystem to gain a better understanding of consciousness, percep-tion, memory, emotion, stress, mental disorders, and self-identity.

• Neurons: basicunits of the nervoussystem, composed ofdendrites, a cell body,and an axon

• Glial cells: hold neu-rons in place as well asnourish, insulate, and protect them

• Nerves: bundles ofaxons and some den-drites in the peripheralnervous system

• Myelin sheath: speedsup the conduction ofneural impulses andprevents adjacent cellsfrom interfering withone another

• Stem cells: seem togive rise to new neu-rons throughout adult-hood (neurogenesis)

Communication between neurons occurs atsynapses, most of which develop after birth:1. Action potential (changes in electrical volt-

age) produces a neutral impulse.2. Neurotransmitter molecules are released

into the synaptic cleft and bind to receptorsites on the receiving neuron.

3. Receiving neuron becomes more likely tofire or less likely to fire.

Neurotransmitters such as serotonin, dopamine, and acetylcholine play a criti-cal role in mood, memory, and psychological well-being.1. Endorphins modify the action of neurotransmitters to reduce pain and

promote pleasure.2. Hormones, chemical substances produced primarily by the endocrine

glands, are released into the bloodstream and affect many organs and cells.• Melatonin promotes sleep.• Oxytocin plays a role in attachment and trust.• Adrenal hormones, such as epinephrine and norepinephrine, are involved in

emotions, memory, and stress.• Sex hormones are involved in the physical changes of puberty; estrogen

and progesterone are involved in the menstrual cycle, and testosterone isinvolved in sexual arousal.

How Neurons Communicate

Chemical Messengers in the Nervous System

The Plastic Brain

Central Nervous System(processes, interprets,

stores information;issues orders to muscles,

glands, organs)

BrainSpinal Cord

(bridge between brainand peripheral nerves)

Nervous System

PeripheralNervous System

(transmits information toand from the CNS)

SomaticNervous System(controls skeletal

muscles)

AutonomicNervous System

(regulates glands, bloodvessels, internal organs)

ParasympatheticNervous System

(conserves energy,maintains quiet state)

SympatheticNervous System(mobilizes body for

action, energy output)

Methods for studying the brain:• Observing patients with brain damage; lesion

method• Electroencephalogram (EEG): brain-wave

recording• Transcranial magnetic stimulation (TMS):

used as a “virtual” lesion method• Positron-emission tomography (PET scan):

method for analyzing biochemical activity inthe brain

• Magnetic resonance imaging (MRI): methodfor studying body and brain tissue, using mag-netic fields and special radio receivers

The Nervous System: ABasic Blueprint

Communication in the Nervous System

Mapping the Brain

• Learning and stimulating environments increase the complexity of synapticconnections, whereas unused connections are pruned away.

• The flexibility of the brain to adapt is known as plasticity, and can accountfor many instances of skill recovery following brain damage.

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The brain stem is inthe lower brain.• The medulla con-

trols automatic functions such as heartbeat andbreathing.

• The pons is in-volved in sleeping,waking, anddreaming.

• The reticular acti-vating system (RAS),a dense network ofneurons, screens in-coming informationand is responsible for alertness.

• The cerebellum contributes to balance and musclecoordination.

• The thalamus directs sensory messages.• The hypothalamus is involved in emotion and drives

vital to survival and controls operations of the auto-nomic nervous system. It controls the pituitarygland, or master gland.

• The limbic system is group of brain areas involvedin emotional reactions and motivated behavior.

• The amygdala evaluates sensory information and de-termines its emotional importance and helps to makethe initial decision to approach or withdraw from a sit-uation.

• The hippocampus plays a critical role in long-termmemory for facts and events.

• The cerebrum contains much of the brain’s circuitry;it is divided into two cerebral hemispheres, connectedby a band of fibers called the corpus callosum. Thecerebrum is covered by thin layers of cells called thecerebral cortex.

All modern brain theories assume localization of function.

Cerebral cortex

Thalamus

Cerebellum

Medulla

Pons

Reticular activatingsystem

Pituitary gland

Hypothalamus

Corpus callosum

Cerebrum

• The occipital lobes contain the visual cortex.• The parietal lobes contain the somatosensory cortex, which

receives information about pressure, pain, touch, and tem-perature.

• The temporal lobes involve memory, perception, and emo-tion.

• The frontal lobes are involved in social judgment, the mak-ing and carrying out of plans, and decision making. Alsocontains the motor cortex, which controls voluntary move-ment, and Broca’s area, which handles speech production.

• The association cortex appears to be responsible for highermental process.

Motor cortex

Frontal lobe

Temporal lobe

Auditory cortex Visualcortex

Occipital lobe

Parietal lobe

Somatosensory cortex

• Lateralization is the specializing of each hemisphere.• The left hemisphere is more active in processing language,

logic, and symbolic–sequential tasks.• The right hemisphere is associated with spatial-visual tasks,

facial recognition, the creation and appreciation of art andmusic, and the processing of negative emotions.

• In most mental activities, the two sides cooperate.

Split Brains

The issue of where the“self” resides in thebrain is unanswered,with some researchersviewing the brain as acollection of inde-pendent modules ormental systems,perhaps with onefunctioning as “inter-preter.” An area ofthe prefrontal cortexmay bind togetherperceptions andmemories thatproduce a senseof self.

Where Is the Self?

Brain scans reveal someanatomical differences inmale and female brains,and sex differences inlateralization duringlanguage tasks. However,the real-life significanceof these and other find-ings remains unclear:• Most supposed gender

differences are stereo-types; the overlap between the sexes isgreater than their differences.

• Small differencesfound in MRI studiesare often unrelated tohow men and womenactually behave orscore on a test.

• Brain differences couldbe a result of sex dif-ferences in behaviorand experience, ratherthan a cause; experi-ence constantly sculptsthe brain.

Are There “His”and “Her” Brains?

Lobes of the Cortex

A Tour through the Brain The Two Hemispheres of the Brain CO

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Two Stubborn Issues in Brain Research

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