Brain Structure and Function

“If the human brain were so simple that we could understand it, we would be so simple that we couldn’t”

-Emerson Pugh, The Biological Origin of Human Values (1977)

Phineas Gage

• September 13th, 1848• Phineas 25 years old • Rutland & Burlington Railroad, Cavendish,

VT• Paving the way for new RR tracks• “Tamping Iron”

– 1.25in x 3ft

• Accident– Quick Recovery

• Months later: “No longer Gage”– Before: capable, efficient, best foreman, well-

balanced mind– After: extravagant, anti-social, liar, grossly

profane• Stint with P.T Barnum• Died 12 years later

Phineas Gage

Evolution of the Brain

Reptilian Paleomammalian Neomammalian

The Brain• Brainstem

–responsible for automatic survival functions

• Medulla–controls heartbeat

and breathing

BRAINSTEM Heart rate and breathing

CEREBELLUM Coordination

and balance

Parts of the Brain

amygdala

pituitary

hippocampusTHALAMUS

Relays messages

Reticular Formation

•Widespread connections •Arousal of the brain as a whole

•Reticular activating system (RAS)

•Maintains consciousness and alertness•Functions in sleep and arousal from sleep

The Cerebellum

–helps coordinate voluntary movement and balance

The Limbic System• Hypothalamus, pituitary,

amygdala, and hippocampus all deal with basic drives, emotions, and memory

• Hippocampus Memory processing

• Amygdala Aggression (fight) and fear (flight)

• Hypothalamus Hunger, thirst, body temperature, pleasure; regulates pituitary gland (hormones)

The Limbic System Hypothalamus

neural structure lying below (hypo) the thalamus; directs several maintenance activities eating drinking body temperature

helps govern the endocrine system via the pituitary gland

linked to emotion

The Limbic System

• Amygdala –two almond-

shaped neural clusters that are components of the limbic system and are linked to emotion and fear

The Brain• Thalamus

– the brain’s sensory switchboard, located on top of the brainstem

– it directs messages to the sensory receiving areas in the cortex and transmits replies to the cerebellum and medulla

The Cerebral Cortex

• Cerebral Cortex –the body’s

ultimate control and information processing center

The lobes of the cerebral hemispheres

The lobes of the cerebral hemispheres

Planning, decision making speech

Sensory

AuditoryVision

The Cerebral Cortex

• Frontal Lobes– involved in speaking and

muscle movements and in making plans and judgments

– the “executive”• Parietal Lobes

– include the sensory cortex

The Cerebral Cortex

• Occipital Lobes – include the visual areas, which

receive visual information from the opposite visual field

• Temporal Lobes – include the auditory areas, each of

which receives auditory information primarily from the opposite ear

The Cerebral Cortex

• Frontal (Forehead to top) Motor Cortex• Parietal (Top to rear) Sensory Cortex• Occipital (Back) Visual Cortex• Temporal (Above ears) Auditory Cortex

Motor/Sensory Cortex

• Contralateral• Homunculus• Unequal

representation

Sensory Areas – Sensory Homunculus

Figure 13.10

The Cerebral Cortex Aphasia

impairment of language, usually caused by left hemisphere damage either to Broca’s area (impairing speaking) or to Wernicke’s area (impairing understanding) –see clips

Broca’s Area an area of the left frontal lobe that directs the

muscle movements involved in speech Wernicke’s Area

an area of the left temporal lobe involved in language comprehension and expression

Language Areas

• Broca Expression

• Wernicke Comprehensionand reception

• AphasiasLEFT HEMISPHERE

Paul Broca [1800s]

• Suggested localization

Techniques to examine functions of the brain

1. Remove part of the brain & see what effect it has on behavior

2. Examine humans who have suffered brain damage

3. Stimulate the brain

4. Record brain activity

Brain Lateralization

Our Divided Brains

• Corpus collosum – large bundle of neural fibers (myelinated axons, or white matter) connecting the two hemispheres

Hemispheric Specialization

LEFT

Symbolic thinking(Language)DetailLiteral meaning

RIGHT

Spatial perceptionOverall pictureContext, metaphor

Contra-lateral division of labor

• Right hemisphere controls left side of body and visual field

• Left hemisphere controls right side of body and visual field

Split Brain Patients

• Epileptic patients had corpus callosum cut to reduce seizures in the brain

• Lives largely unaffected, seizures reduced• Affected abilities related to naming objects

in the left visual field

Brain Plasticity

Brain Plasticity

• The ability of the brain to reorganize neural pathways based on new experiences

• Persistent functional changes in the brain represent new knowledge

• Age dependent component• Brain injuries

Environmental influences on neuroplasticity

Impoverished environment

Enriched environment

Sensation and Perception

Sensation

• The process by which the central nervous system receives input from the environment via sensory neurons

• Bottom up processing

Perception

• The process by which the brain interprets and organizes sensory information

• Top-down processing

The psychophysics of sensation

• Absolute threshold the minimum stimulation needed to detect a stimulus with 50% accuracy

• Subliminal stimulation below the absolute threshold for conscious awareness– May affect behavior without conscious

awareness• Sensory adaptation/habituation

diminished sensitivity to an unchanging stimulus

The five major senses• Vision – electromagnetic

– Occipital lobe• Hearing – mechanical

– Temporal lobe• Touch – mechanical

– Sensory cortex• Taste – chemical

– Gustatory insular cortex • Smell – chemical

– Olfactory bulb– Orbitofrontal cortex– Vomeronasal organ?

The sixth sense

• Vestibular balance and motion– Inner ear

• Proprioceptive relative position of body parts– Parietal lobe

• Temperature heat– Thermoreceptors throughout the body, sensory cortex

• Nociception pain– Nociceptors throughout the body, sensory cortex

And the seventh…and eighth…and ninth…

Thresholds of the five major senses

The Retina

The retina at the back of the eye is actually part of the brain!

Rods – brightnessCones – color