Invitation to Psychology

138 Chapter 4 Neurons, Hormones, and the Brain

In 1953, Ronald E. Myers and Roger W. Sperry

took the first step toward answering this question

by severing the corpus callosum in cats. They also

cut parts of the nerves leading from the eyes to

the brain. Normally, each eye transmits messages

to both sides of the brain. After this procedure, a

cat’s left eye sent information only to the left hemi-

sphere and its right eye sent information only to

the right hemisphere.

At first, the cats did not seem to be affected

much by this drastic operation. But Myers and

Sperry showed that something profound had hap-

pened. They trained the cats to perform tasks with

one eye blindfolded; a cat might have to push a

panel with a square on it to get food but ignore a

panel with a circle. Then the researchers switched

the blindfold to the cat’s other eye and tested the

animal again. Now the cats behaved as if they had

never learned the trick. Apparently, one side of the

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 other spe-

cies, including monkeys (Sperry, 1964).

In all of the animal studies, ordinary behavior,

such as eating and walking, remained normal. In

the early 1960s, a team of surgeons decided to try

cutting the corpus callosum in patients with debili-

tating, uncontrollable epilepsy. In severe forms of

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”

are exaggerations.

the two hemispheres

of the Brain Lo 4.14

We have seen that the cerebrum is divided into

two hemispheres that control opposite sides of the

body. Although similar in structure, these hemi-

spheres have somewhat separate talents, or areas

of specialization.

Split Brains: a House Divided

In a normal brain, the two hemispheres communi-

cate with one another across the corpus callosum,

the bundle of fibers that connects them. Whatever

happens in one side of the brain is instantly flashed

to the other side. What would happen, though, if

the two sides were cut off from one another?

Recite & Review

Recite: Using your own brain, say out loud everything you can about localization of function, and

the brain stem, RAS, cerebellum, thalamus, hypothalamus, pituitary gland, amygdala, hippocampus,

cerebrum, corpus callosum, lateralization, cerebral cortex, lobes of the cortex, and prefrontal cortex.

Review: Next, go back and read this section again. What did you miss?

Now take this Quick Quiz:

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

Study and Review at mypsychlab

1. Filters out irrelevant information


2. Known as the “gateway to memory”


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


4. Consists of two hemispheres


5. Wrinkled outer covering of the cerebrum


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

a. reticular activating system

b. cerebrum

c. hippocampus

d. cerebral cortex

e. frontal lobes

f. hypothalamus

B. Why might the same perception of the same potential danger produce a different response in

the amygdala in two different people?

Answers:

Because of differences in their personality traits or current psychological state. B. e6. d5. b4. f 3. c2. a1. A.