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Emotion involves the entire nervous
system, of course. But there are two parts
of the nervous system that are especiallysignificant:
limbic system
autonomic nervous system
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The limbic system is a complex set of structures that lies on both sides of thethalamus, just under the cerebrum. It includes
the hypothalamus, the hippocampus, theamygdala, and several other nearby areas. Itappears to be primarily responsible for our emotional life, and has a lot to do with the
formation of memories.
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In this drawing, you are looking at the brain cut in half, but
with the brain stem intact. The part of the limbic system
shown is that which is along the left side of the thalamus
(hippocampus and amygdala) and just under the front of thethalamus (hypothalamus):
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The hypothalamus is a small part of the brain located just below thethalamus on both sides of the third ventricle.
The hypothalamus is one of the busiest parts of the brain, and is mainly
concerned with homeostasis. Homeostasis is the process of returning
something to some “set point.” It works like a thermostat.
The hypothalamus is responsible for regulating your hunger, thirst, responseto pain, levels of pleasure, sexual satisfaction, anger and aggressive behavior,
and more.
It also regulates the functioning of the autonomic nervous system, which in
turn means it regulates things like pulse, blood pressure, breathing, and
arousal in response to emotional circumstances.
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The hippocampus consists of two “horns” that curve back from the amygdala. It appears to be veryimportant in converting things that are “in your mind”at the moment (in short-term memory) into things that
you will remember for the long run (long-termmemory). If the hippocampus is damaged, a personcannot build new memories, and lives instead in astrange world where everything they experience justfades away, even while older memories from the time
before the damage are untouched!
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The amygdalas are two almond-shaped masses of neurons on either side of the thalamus at the lower endof the hippocampus. When it is stimulated electrically,animals respond with aggression. And if the amygdalais removed, animals get very tame and no longer respond to things that would have caused rage
before. But there is more to it than just anger: Whenremoved, animals also become indifferent to stimulithat would have otherwise have caused fear and even
sexual responses.
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The cingulate gyrus is the part of the cerebrum that lies closest to the limbic system, just
above the corpus collosum. It provides a pathway from the thalamus to the hippocampus,seems to be responsible for focusing attention on emotionally significant events, and for
associating memories to smells and to pain.
The ventral tegmental area of the brain stem (just below the thalamus) consists of dopamine
pathways that seem to be responsible for pleasure. People with damage here tend to have
difficulty getting pleasure in life, and often turn to alcohol, drugs, sweets, and gambling.
The basal ganglia (including the caudate nucleus, the putamen, the globus pallidus, and the
substantia nigra) lie over and to the sides of the limbic system, and are tightly connected with
the cortex above them. They are responsible for repetitive behaviors, reward experiences,
and focusing attention. If you are interested in learning more about the basal ganglia,
The prefrontal cortex, which is the part of the frontal lobe which lies in front of the motor
area, is also closely linked to the limbic system. Besides apparently being involved in
thinking about the future, making plans, and taking action, it also appears to be involved in
the same dopamine pathways as the ventral tegmental area, and plays a part in pleasure and
addiction.
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The second part of the nervous system to havea particularly powerful part to play in our emotional life is the autonomic nervous
system. The autonomic nervous system iscomposed of two parts, which function primarily in opposition to each other.
sympathetic nervous system
parasympathetic nervous system
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Activation of the sympathetic nervous system has the
following effects:
dilates the pupils
opens the eyelids
stimulates the sweat glands
dilates the blood vessels in large muscles
Constricts blood vessels in the rest of the body
increases the heart rate
opens up the bronchial tubes of the lungs
inhibits the secretions in the digestive system
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Some of the details of parasympathetic arousalinclude...
pupil constriction
activation of the salivary glands
stimulating the secretions of the stomach
stimulating the activity of the intestines
stimulating secretions in the lungsconstricting the bronchial tubes
decreasing heart rate
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The basal ganglia are a collection of nucleifound on both sides of the thalamus, outsideand above the limbic system, but below the
cingulate gyrus and within the temporallobes. Although glutamate is the mostcommon neurotransmitter here as everywherein the brain, the inhibitory neurotransmitter
GABA plays the most important role in the basal ganglia.
Th l f h l i ll d h
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The largest group of these nuclei are called the corpus
striatum ("striped body"), made up of
the caudate nucleus ("tail"), the putamen ("shell"),
the globus pallidus ("pale globe"), and the nucleus
accumbens ("leaning"). All of these structures a double ones,one set on each side of the central septum.
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The caudate begins just behind the frontal lobe and curves back towards the
occipital lobe. It sends its messages to the frontal lobe (especially the orbital
cortex, just above the eyes), and appears to be responsible for informing us
that something is not right and we should do something about it: Wash your
hands! Lock your door! As these examples are meant to suggest, obsessivecompulsive disorder (OCD) is likely to involve an overactive caudate. On
the other hand, an underactive caudate may be involved in various disorders,
such as ADD, depression, aspects of schizophrenia, and just plain
lethargy. It is also involved in PAP syndrome, a dramatic loss of
motivation only recently discovered.
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The putamen lies just under and behind the
front of the caudate. It appears to be
involved in coordinating automatic behaviors
such as riding a bike, driving a car, or
working on an assembly line. Problems with
the putamen may account for the symptoms
of Tourette's syndrome.
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The globus pallidus is located just
inside the putamen, with an outer
part and an inner part. It receivesinputs from the caudate and
putamen and provides outputs to the
substantia nigra.
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The nucleus accumbens is a nucleus just
below the previous nuclei. It receives signals
from the prefrontal cortex (via the ventral
tegmental area) and sends other signals back there via the globus pallidus. The inputs use
dopamine, and many drugs are known to
greatly increase these messages to the nucleusaccumbens.
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Another nucleus of the basal ganglia is the substantia
nigra ("black substance"). Located in the upper
portions of the midbrain, below the thalamus, it gets its
color from neuromelanin, a close relative of the skin
pigment. One part (the pars compacta) uses dopamine
neurons to send signals up to the striatum. The exact
function isn't known, but is believed to
involve reward circuits. Also, Parkinson's
disease is due to the death of dopamine neurons here.
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As you can see, quite a few serious problems
are strongly associated with the basalganglia. Some, such as:
Parkinson's disease
Huntington's diseaseCerebral palsy
PAP ( or Athymhormic) syndrome
Schizophrenia
Obsessive Compulsive Disorder (OCD)
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The cerebrum -- which is just Latinfor "brain" -- is the newest
(evolutionarily) and largest part of the brain as a whole. It is here thatthings like perception, imagination,
thought, judgment, and decisionoccur.
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The surface of the cerebrum -- the cerebral cortex -- is composed
of six thin layers of neurons, which sit on top of a large collection
of white matter pathways. The cortex is heavily convoluted, so
that if you were to spread it out, it would actually take up about 2
1/2 square feet (2500 sq cm). It includes about 10 billion neurons,
with about 50 trillion synapses!
The convolutions have "ridges" which are called gyri, and
"valleys" which are called sulci. Some of the sulci are quite
pronounced and long, and serve as convenient boundaries between four areas of the cerebrum called lobes.
The furthest forward is the frontal lobe (from the Latin word for
forehead). It seems to be particularly important: This lobe is
responsible for voluntary movement and planning and is thoughtto be the most significant lobe for personality and intelligence.
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At the back portion of the frontal lobe, along the sulcus that separates itfrom the parietal lobe, is an area called the motor cortex. In studies with
brain surgery patients, stimulating areas of the motor cortex with tinyelectrical probes caused movements. The lowest portions of the motor cortex, closest to the temples, control the muscles of the mouth andface. The portions of the motor cortex near the top of the head control thelegs and feet.
At the side of the head is the temporal lobe (from the Latin word for temple). The special area of the temporal lobe is the auditory cortex. Asthe name says, this area is intimately connected with the ears and
specializes in hearing. It is located near to the temporal lobe's connectionswith the parietal and frontal lobes.
At the back of the head is the occipital lobe. At the very back of theoccipital lobe is the visual cortex, which receives information from theeyes and specializes, of course, in vision.
The areas of the lobes that are not specialized are called associationcortex. Besides connecting the various sensory and motor cortices, this isalso believed to be where our thought processes occur and many of our memories are ultimately stored.
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Behind the frontal lobe is
the parietal lobe (from a Latin
word meaning wall). It includes
an area called the somatosensory
cortex, just behind the sulcusseparating this lobe from the
frontal lobe. Again, doctors
stimulating points of this area
found their patients describing
sensations of being touched atvarious parts of their bodies. Just
like the motor cortex, the
somatosensory cortex can be
mapped, with the mouth and face
closest to the temples and the legs
and feet at the top of the head.
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If you look at the brain from the previousslide, it becomes immediately obvious that
it is split in two from front to back. There
are, in fact, two hemispheres, almost as if we have two brains in our heads instead of
just one. Of course, these two halves are
intimately linked together with an arch of white matter called the corpus callosum.
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The right hemisphere is the
one that relates to the left side
of the body.The right hemisphere has
more to do with things like
spatial orientation, face
recognition, and body
image. It also seems to govern
our ability to appreciate art and
music.
It is the left hemisphere that
relates to the right side of the
body (generally).The left hemisphere usually
has language, and seems to
be primarily responsible for
similar systems such as mathand logic.
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If you would flash things on a
projection screen and ask the
patients with epilepsy to either say
what they saw or pick what they
saw with one hand or the other from a box full of things. So, if
he showed a ball on the left side
of the screen and a pencil on the
right, the person would say
"pencil" (using the lefthemisphere's speech centers) but
pick a ball from the box with his
or her left hand (using the right
hemisphere)!
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So, speech is predominantly a function of the lefthemisphere. Actually, the right hemisphere does
have a little bit of speech, too: It has a good grasp of
names and curse words! In addition, if you have
brain damage to the left hemisphere early enough inchildhood, the right hemisphere will take over the
speech function. And it seems that there are some
people who have language on the right or even on
both sides.
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Another area is Wernicke's area, which
is nearby Broca's area but in the temporal
lobe, right next to the auditory cortex.
This is were we understand the `meaning
of speech, and damage to this area will
leave you with raeceptive aphasia,meaning that you will be unable to
understand what is being said to you.
Occasionally, someone has damage to the
connections between Broca's and
Wernicke's areas. This leads
to conduction aphasia. Someone with
this problem can understand speech just
fine, and can produce it as well. They justcan't repeat something they just heard!
Another important area is the angular
gyrus, just above and behind Wernicke's
area. It serves as the connection between
the language centers and the visual
cortex. If this area is damaged, the person
will suffer from alexia (inability to read)
and agraphia (inability to write).
One of the earliest things discovered about
the brain were the speech centers. One is
called Broca's area, It is located at the
bottom of the left frontal lobe. A patient
who had damage to this area lost hisability to speak, which is
called expressive aphasia.
A f f th f t l t
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Starting from the central sulcus and
working forward, we first have
the motor cortex, which sends its
signals down to the body to control
the skeletal muscles.
Just in front of the motor cortex there
is the premotor cortex, which is
where we compose and rehearse
movements before we engage in
them. Broca's area for speech
production is part of the premotor cortex.
And then we have the prefrontal
cortex, where some of the most
interesting things occur. Some say
that will power, our sense of reality,
and our sense of our own personalityreside there.
A few areas of the prefrontal cortexare at least partiallyunderstood. The dorsolateral area(high and to the sides) appears toallow us to hold ideas in awareness,focus on them, and even manipulate
them.The ventromedial area (low andclose to the midline) seems to beinvolved in emotional experience and provides us with the feeling thatthings make sense and have meaning.
The orbital area of the prefrontalcortex (just above the eyeballs) tellsus when something is wrong andrequires serious attention. It also hasthe ability to inhibit behaviors that areinappropriate, such as those that areharmful to us or are sociallyunacceptable. This includes the
ability to counteract the signals for aggression from the amygdala in thelimbic system.
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Starting from the central sulcus and working forward, we first have the motor cortex, which sends
its signals down to the body to control the skeletal muscles.Just in front of the motor cortex there is the premotor cortex, which is where we compose andrehearse movements before we engage in them. Broca's area for speech production is part of the
premotor cortex.
And then we have the prefrontal cortex, where some of the most interesting things occur. Somesay that will power, our sense of reality, and our sense of our own personality reside there.
A few areas of the prefrontal cortex are at least partially understood. The dorsolateral area (highand to the sides) appears to allow us to hold ideas in awareness, focus on them, and even manipulate
them.The ventromedial area (low and close to the midline) seems to be involved in emotional experienceand provides us with the feeling that things make sense and have meaning. Low levels of activityhere are associated with depression: Nothing makes any sense. High levels, on the other hand, areassociated with mania: Every little thing is full of importance!
The orbital area of the prefrontal cortex (just above the eyeballs) tells us when something is wrongand requires serious attention. It also has the ability to inhibit behaviors that are inappropriate, suchas those that are harmful to us or are socially unacceptable. This includes the ability to counteract
the signals for aggression from the amygdala in the limbic system. It is believed that many violentcriminals have had damage to this area of the brain.
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This lobe sits at the two sides of the head, under the temples. The upper partof the temporal lobe, along the Sylvian fissure that separates it from the
frontal lobe, is the primary auditory cortex, which receives input from
cochlea. The areas around it are devoted to interpreting sounds, and one of
these in particular (Wernicke's area, toward the boundary with the parietal
lobe in the left hemisphere) is known to be devoted to the understanding of
language.
Another area is called the fusiform gyrus, which sits low in the temporal
lobe near the occipital lobe. In the left hemisphere, it is responsible for word
and number recognition. In the right hemisphere, it is responsible for the
crucial human ability to recognize faces. Problems here leave one with a
disorder called prosopagnosia ("face blindness"), which makes social life
very difficult.
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The furthest forward area of the parietal lobe,along the central gyrus nearest the frontal lobe, isthe somatosensory area, which collects signalscoming up from the body. Just behind that is the
somatosensory association area, which further analyzes these bodily sensations. Specific areasspecialize in locating and orienting us in three-dimensional space, and focusing on things in the
outside world.
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The occipital lobe is the smallest of the lobes and sits at the very back of the head. It has no clear borders and is differentiated primarily by function,i.e. vision. The various parts of the occipital lobe are labeled with a V (for visual) followed by a number.
Theprimary visual cortex at the very back of the occipital lobe islabeled V1, and receives input from the optic tract. It has a clear map of
visual information that corresponds to the areas of the retina. The center of vision is greatly magnified. The individual neurons of V1 are extremelysensitive to very particular changes in input from the eyes.
If there is a lesion somewhere in V1, there will be a "hole" in your visioncalled a scotoma. Oddly, some of the information from that "hole" seemsto still be available, so that some people with scotomas can still react to
stimuli there even though they don't consciously perceive them! This iscalled blindsight.
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The cingulate gyrus sits below the rest of the cerebralcortex, up against the corpus callosum and partiallycovering lower areas such as the basal ganglia, thelimbic system, and the thalamus. Many people see it asthe fifth lobe - others see it as part of the lobes above it,
particularly the frontal lobe. It is so intimatelyconnected with the limbic system that it is sometimescalled the limbic gyrus. One of its major jobs is to keepyour attention focused. When it isn't functioning
properly, as seems to happen in schizophrenia, you areunable to distinguish real voices from imaginary ones.
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