HUMAN BIOLOGY

254 Chapter 13

a Closer Look at the Cerebrum

Each hemisphere also is divided into lobes that process

different signals. The lobes are the frontal, occipital, tempo-

ral, and parietal lobes (Figure 13.18A). EEGs and PET scans

(Figure 13.18B) can reveal activity in each lobe. EEG, short

for electroencephalogram, is a recording of electrical activ-

ity in some part of the brain.

the cerebral cortex is the seat

of consciousness

Your thoughts, memories, the ability to understand, and

voluntary acts all begin in the cerebral cortex. The cor-

tex is divided into three main parts. Motor areas control

voluntary movements. Sensory areas govern the ability to

grasp the meaning of sensations (that is, information from

sensory organs). Association areas process information as

needed to produce a conscious action.

Motor areas In the frontal lobe of each hemisphere, the

whole body is spatially mapped out in the primary motor

cortex. This area controls coordinated movements of skel-

etal muscles. Thumb, finger, and tongue muscles get much

of the area’s attention, indicating how much control is

required for voluntary hand movements and verbal expres-

sion (Figure 13.19).

Also in the frontal lobe are the premotor cortex, Broca’s

area, and the frontal eye field. The premotor cortex deals

with learned patterns or motor skills. Repetitive motor

actions, such as bouncing a ball, are evidence that your

motor cortex is coordinating the movements of several

muscle groups. Broca’s area (usually in the left hemisphere)

and a corresponding area in the right hemisphere control

the tongue, throat, and lip muscles used in speech. It kicks

in when we are about to speak and even when we plan

voluntary motor activities other than speaking (so you can

talk on the phone and write down a message at the same

time). Above Broca’s area is the frontal eye field. It controls

voluntary eye movements.

n Our capacity for conscious thought and language arises

from the activity of the cerebral cortex.

n The cortex interacts with other brain regions to shape our

emotional responses and memories.

Each cerebral hemisphere has a deeply folded, outer layer

of gray matter, the cerebral cortex. It is a layer of gray

matter about 2–4 millimeters, or one-eighth inch, thick.

Below the cortex are the white matter (axons) and the basal

nuclei, which are patches of gray matter in the thalamus.

Each cerebral hemisphere receives and processes sig-

nals mainly from the opposite side of the body. For

example, “cold” signals from an ice

cube in your left hand travel to

your right cerebral hemisphere, and

vice versa. Overall, the left hemi-

sphere deals mainly with speech,

analytical skills, and mathematics.

In most people it dominates the right

hemisphere, which deals more with

visual–spatial relationships, music,

and other creative activities.

Motor cortex activity

when speaking

Prefrontal cortex activity

when writing words

Visual cortex activity

when reading

F i g u r e 13.18 The cerebrum is divided into hemispheres and lobes. a Lobes of the

brain, showing the primary receiving and integrating centers of the cerebral cortex.

B PET scans show brain regions that were active when a subject performed three

specific language tasks: speaking, writing words, and reading.

B

Marcus Raichle, Washington University School of Medicine

13.8

primary

motor

cortex

primary

somatosensory

cortex

parietal

lobe

(sensations

from internal

organs)

temporal lobe (hearing,

advanced visual processing)

occipital lobe

(vision)

Broca’s area

frontal lobe

(planning of

movements,

aspects of

memory,

inhibition of

unsuitable

behaviors) Wernicke’s

area

a

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© Cengage Learning

cerebral cortex The outer
layer of gray matter of each
cerebral hemisphere.

limbic system The brain
region that governs emo-
tions and influences related
behavior. It includes parts
of the thalamus, hypothala-
mus, the amygdala, and the
hippocampus.

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