The BRAIN -- how do we find out things about it?

Certain kinds of BRAIN DAMAGE produce certain impairments, which allows us to map areas of the brain to their functions.

We can also ELECTRICALLY STIMULATE the brain, again to map areas to their functions (not in book).

EEG -- a reading of the patterns of the brain's electrical activity (BRAINWAVES) (not in book).

MRI SCAN -- measuring emissions from H nuclei that are placed in strong magnetic fields -- produces a picture of the brain's structure (there's also a more modern FUNCTIONAL MRI (fMRI) that shows levels of activity).

PET SCAN -- measuring the emissions of radioactively labeled glucose introduced into the brain -- produces a picture of the levels of the brain's neural activity.

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Now, let's look at the NERVOUS SYSTEM as a whole, which comprises:

I. The CENTRAL NERVOUS SYSTEM (CNS) (the brain and spinal cord)

II. The PERIPHERAL NERVOUS SYSTEM (PNS) (everything else), which comprises:

A. The SOMATIC NERVOUS SYSTEM (for voluntary muscular control),

B. The AUTONOMIC NERVOUS SYSTEM (for control of self-regulating functions, such as heartbeat, breathing, etc.), which comprises:
 
 
 
 

1. The SYMPATHETIC NERVOUS SYSTEM (which arouses the body for action),

2. The PARASYMPATHETIC NERVOUS SYSTEM (which calms the body).

-- the sympathetic and parasympathetic systems operate together to produce a state of HOMEOSTASIS -- a balance with respect to the demands we’re experiencing.

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The Brain's Structures

I. The BRAINSTEM -- a collection of structures that constitute the "oldest" (in terms of evolution) and innermost (physically) parts of the brain.

PONS -- the structural bridge between the spinal cord and the brain

MEDULLA -- basic autonomic functions, such as breathing and heartbeat.

RETICULAR FORMATION -- controls arousal (damage here eventually produces a coma, whereas electrical stimulation produces instant alertness).

THALAMUS -- functions as the brain's switchboard, routing messages between the brain's lower and higher regions.

CEREBELLUM -- coordinates voluntary movement (such as walking).

II. LIMBIC SYSTEM -- a group of structures generally involved in basic motives, such as emotions, hunger & thirst, and sex-drive.

HIPPOCAMPUS -- a structure involved in memory.

AMYGDALA -- involved in aggression and fear (fight or flight) responses.

HYPOTHALAMUS -- involved in hunger, thirst, body temp., sexual behavior. Also provides the brain's primary interface to the pituitary gland (and hence to the endocrine system).
 
 

-- in some animals, a great pleasure center. E.g., if an electrode is placed in a rat's hypothalamus and connected to a lever, the rat will continually press the lever until physically exhausted.

-- in human beings, it's also a pleasure center, although it doesn't produce the frenzies it does in rats.

III. CEREBRAL CORTEX -- the physically outermost and "newest" (in terms of evolution) outer covering of the brain. Complex human functions like learning, thinking and adaptability.

-- divided into 4 areas called LOBES
 
 

A. FRONTAL LOBES (behind forehead):

-- an “executive function” -- planning, decision-making, organizing

-- associated with personality, as in the case of Phineas Gage (for whom damage to frontal lobes produced great changes in personality).

-- contains the MOTOR CORTEX (at very rear of frontal lobes)

-- controls voluntary motor function; stimulation causes mov't.

-- areas of the body that require precise mov't (such as hands) have

larger areas of motor cortex devoted to them.

One can map movement to areas here to produce a “MOTOR HOMUNCULUS,” a drawing of the body in terms of the areas of motor cortex devoted to it.

-- the left part of the motor cortex controls the right half of the body, and vice versa -- a kind of cross-connection.

-- contains (usually in the left hemisphere) BROCA’S AREA, which controls the vocal areas of the motor cortex to produce spoken speech.
 
 

-- damage to Broca’s area produces BROCA’S APHASIA (Aphasia =

disturbance in language use due to brain damage), where a person can understand language, but can‘t generate coherent speech.
 
 

B. PARIETAL LOBES (at top & rear of brain)

-- Contains the SOMATOSENSORY CORTEX (at very front edge of parietal lobes)

-- receives and processes tactile (i.e., touch) sensation

-- more sensitive areas of the body (such as lips) have larger areas of sensory cortex devoted to them.

So, one can also draw a “SENSORY HOMUNCULUS,” that’s analogous to the motor homunculus.

-- the left part of the sensory cortex processes the right half of the

body, and vice versa -- again, a kind of cross-connection.
 
 

C. TEMPORAL LOBES (at temples, above ears)

-- contains specialized areas for processing auditory information
 
 

-- contains WERNICKE’S AREA, an area specialized in understanding the content & meaning of language.

Damage here produces WERNICKE’S APHASIA, where a person is able to generate individual words, but isn’t able to put them together in

a way that makes sense.

-- contains the ANGULAR GYRUS, an area specialized in visual forms of language like reading & writing.

D. OCCIPITAL LOBES (at back of head)

-- processing of vision -- colors, recognizing sights, etc.

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The ENDOCRINE SYSTEM also affects brain function (and vice versa).

- the endocrine system is composed of various GLANDS that secrete

HORMONES that can affect moods and other responses (such as sex, food,

aggression).

- generally, the glands of the endocrine system (e.g., thyroid, pancreas, adrenal glands, gonads) are controlled by the PITUITARY GLAND which also provides a connection to the brain via the hypothalamus.

- the endocrine system and brain operate in concert with one another to form a kind of FEEDBACK LOOP:

(brain --> pituitary --> other glands --> hormones --> brain)

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The 2 HEMISPHERES (left and right) of the cerebral cortex have somewhat different functions.
 
 

- Usually damage to a person’s left hemispheres produces greater impairment.

- One source of info. about the hemispheres comes from SPLIT-BRAIN OPERATIONS, where the CORPUS CALLOSUM (the nerve trunk

connecting the hemispheres) is surgically severed.

- these patients seem normal at first, but…

- if you put something in a patient's left hand (without his seeing it), he would deny that it was there. Why?

The right hemisphere can feel the object, but it doesn’t have control of language. The left hemisphere can’t be told the object’s there, and so it says (since it has language) that nothing’s there.

There are similar results with visual experiments:

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| H E . A R T |

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- after focusing on the dot, a split-brain patient is asked to say what he sees. He'll say "ART" (since it's in the right half of his visual field, which gets fed to his left hemisphere -- where language is).

- but if asked to point with his left hand to what he sees, he'll point to "HE" (since the right hemisphere is processing the left half of the visual field, and also controls the left hand).

- there are similar results where we sedate one hemisphere only of a non-split-brain person (not in book).

Generally, the left hemisphere is better at verbal, mathematical and analytical tasks, and the right hemisphere is better at spatial and holistic tasks, such as copying drawings, recognizing emotions in people's faces, etc.