Invitation to Psychology

136 Chapter 4 Neurons, Hormones, and the Brain

are particularly sensitive. Parts of the parietal

lobes are also involved in attention and spatial

awareness.

•   The temporal lobes (from the Latin for “per-

taining to the temples”) are at the sides of

the brain, just above the ears and behind the

temples. They are involved in memory, percep-

tion, and emotion, and they contain the audi-

tory cortex, which processes sounds. An area of

the left temporal lobe known as Wernicke’s area

is involved in language comprehension.

•   The frontal lobes, as their name indicates, are

located toward the front of the brain, just under

the skull in the area of the forehead. They con-

tain the motor cortex, which issues orders to the

600 muscles of the body that produce voluntary

movement. In the left frontal lobe, a region

known as Broca’s area handles speech produc-

tion. During short-term memory tasks, areas in

the frontal lobes are especially active. The fron-

tal lobes are also involved in emotion and in the

ability to make plans, think creatively, and take

initiative.

Because the lobes of the cerebral cortex have

different functions, they tend to respond differ-

ently when directly stimulated by electrodes dur-

ing brain surgery. (The brain does not feel touch

or pain, so the patient can be awake.) If a surgeon

stimulates the somatosensory cortex in the parietal

lobes, a patient might feel a tingling in the skin or

a sense of being gently touched there. If the vi-

sual cortex in the occipital lobes were stimulated,

the person might report seeing a flash of light

or swirls of color. And, eerily, many areas of the

cortex, when stimulated, would produce no obvi-

ous response or sensation. These “silent” areas are

sometimes called the association cortex because they

are involved in higher mental processes.

Watch the Video The Basics: How the Brain

Works, Part 2 at mypsychlab

The Prefrontal Cortex. The most forward part

of the frontal lobes is the prefrontal cortex. This area

barely exists in mice and rats and takes up only 3.5

percent of the cerebral cortex in cats and about 7

percent in dogs, but it accounts for approximately

one-third of the entire cortex in human beings. It

is the most recently evolved part of our brains and

is associated with such complex abilities as reason-

ing, decision making, and planning.

Scientists have long known that the fron-

tal lobes, and the prefrontal cortex in particular,

must also have something to do with personality.

The first clue appeared in 1848, when a bizarre

parietal [puh-rYe-uh-
tuhl] lobes Lobes at the
top of the brain’s cerebral
cortex; they contain areas
that receive information
on pressure, pain, touch,
and temperature, and
that are involved in at-
tention and awareness of
spatial relationships.

temporal lobes Lobes

at the sides of the brain’s

cerebral cortex; they

contain areas involved in

hearing, memory, percep-

tion, emotion, and (in the

left lobe, typically) lan-

guage comprehension.

frontal lobes Lobes at
the front of the brain’s
cerebral cortex; they
contain areas involved
in short-term memory,
higher-order thinking, ini-
tiative, social judgment,
and (in the left lobe, typi-
cally) speech production.

The Cerebral Cortex. Working our way right

up through the top of the brain, we find that

the cerebrum is covered by several thin layers

of densely packed cells known collectively as the

cerebral cortex. Cell bodies in the cortex, as in many

other parts of the brain, produce a grayish tissue,

hence the term gray matter. In other parts of the

brain (and in the rest of the nervous system), long,

myelin-covered axons prevail, providing the brain’s

white matter. Although the cortex is only about

3 millimeters (1/8 inch) thick, it contains almost

three-fourths of all the cells in the human brain.

The cortex has many deep crevasses and wrinkles,

which enable it to contain its billions of neurons

without requiring us to have the heads of giants—

heads that would be too big to permit us to be born.

In other mammals, which have fewer neurons, the

cortex is less crumpled; in rats, it is quite smooth.

Lobes of the Cortex. In each cerebral hemi-

sphere, deep fissures divide the cortex into four

distinct regions, or lobes (see Figure 4.9):

•   The occipital lobes (from the Latin for “in back

of the head”) are at the lower back part of the

brain. Among other things, they contain the

visual cortex, where visual signals are processed.

Damage to the visual cortex can cause impaired

visual recognition or blindness.

•   The parietal lobes (from the Latin for “pertain-

ing to walls”) are at the top of the brain. They

contain the somatosensory cortex, which receives

information about pressure, pain, touch, and

temperature from all over the body. The ar-

eas of the somatosensory cortex that receive

signals from the hands and the face are dis-

proportionately large because these body parts

cerebral cortex A col-
lection of several thin
layers of cells covering
the cerebrum; it is largely
responsible for higher
mental functions; cortex
is Latin for “bark” or
“rind.”

occipital [ahk-SiP-
uh-tuhl] lobes Lobes
at the lower back part
of the brain’s cerebral
cortex; they contain ar-
eas that receive visual
information.

Motor cortex

Frontal lobe

Temporal lobe

Auditory cortex

Visual

cortex

Occipital lobe

Parietal lobe

Somatosensory cortex

Figure 4.9 Lobes of the Cerebrum

Deep fissures divide the cortex of each cerebral hemi-

sphere into four regions.