The hindbrain includes the upper part of the spinal cord,
the brain stem, and a wrinkled ball of tissue called the cerebellum (1) . The hindbrain controls the body’s
vital functions such as respiration and heart rate. The
cerebellum is responsible for learned rote movements.
When you play the piano or hit a tennis ball you are
activating the cerebellum. Above the hindbrain lies the
midbrain, which controls some reflex actions and is part
of the circuit responsible for voluntary movements.
The forebrain is the largest and most highly developed
part of the human brain; it consists primarily of the
cerebrum and the structures hidden beneath it
(see "The Inner Brain").
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When people see pictures of the brain it is usually the
cerebrum that they notice. The cerebrum sits at the
outermost part of the brain and is the source of
intellectual activities. It holds your memories, allows you
to plan, enables you to imagine and think. It allows you
to recognize friends, read books, and play games.
The cerebrum(2) is split into two halves (hemispheres) by
a deep fissure. Despite the split, the two cerebral
hemispheres communicate with each other through a
thick tract of nerve fibers that lies at the base of this
fissure. Although the two hemispheres seem to be mirror
images of each other, they are different. For instance, the
ability to form words seems to lie primarily in the left
hemisphere, while the right hemisphere seems to control
many abstract reasoning skills.
For some unknown reason, nearly all of the signals from
the brain to the body and vice-versa cross over on their
way to and from the brain. This means that the right
cerebral hemisphere primarily controls the left side of the
body and the left hemisphere primarily controls the right
side. When one side of the brain is damaged, the opposite
side of the body is affected. For example, a stroke in
the right hemisphere of the brain can leave the left arm
and leg paralyzed. The Geography of Thought
Each cerebral hemisphere can be divided into sections,
or lobes, each of which specializes in different functions.
To understand each lobe and its specialty we will take a
tour of the cerebral hemispheres, starting with the two frontal lobes (3), which lie directly behind the forehead.
When you plan a schedule, imagine the future, or
use reasoned arguments, these two lobes are working.
One of the ways the frontal lobes seem to do these things
is by acting as short-term storage sites, allowing one idea
to be kept in mind while other ideas are considered.
In the rear portion of each frontal lobe is a motor area(4) , which helps control voluntary
movement. A nearby place on the left frontal lobe called Broca’s area (5) allows thoughts to be transformed
into words.
When you enjoy a good meal—the taste, aroma, and
texture of the food—two sections behind the frontal lobes
called the parietal lobes (6) are at work. The
forward parts of these lobes, just behind the motor areas,
are the primary sensory areas (7) . These areas
receive information about temperature, taste, touch,
and movement from the rest of the body. Reading and
arithmetic are also functions in the repertoire of each
parietal lobe.
As you look at the words and pictures on this page, two
areas at the back of the brain are at work. These lobes,
called the occipital lobes (8), process images
from the eyes and link that information with images
stored in memory. Damage to the occipital lobes can
cause blindness.
The last lobes on our tour of the cerebral hemispheres
are the temporal lobes (9) , which lie in front of
the visual areas and nest under the parietal and frontal
lobes. Whether you appreciate symphonies or rock
music, your brain responds through the activity of these
lobes. At the top of each temporal lobe is an area
responsible for receiving information from the ears.
The underside of each temporal lobe plays a crucial role
in forming and retrieving memories, including those
associated with music. Other parts of this lobe seem
to integrate memories and sensations of taste, sound,
sight, and touch.
