The Forebrain

The Central Nervous System: Making Sense of the World
63
The cerebellum is involved in the balance and
coordination required for walking. When
the cerebellum’s activity is impaired by
alcohol, these skills are disrupted, which
is why the police ask suspected drunk
drivers to walk a straight line.
A FIELD SOBRIETY TEST
The Midbrain
A small region called the midbrain lies above the hindbrain. If you focus your eyes on
another person and then move your head, midbrain circuits allow you to move your
eyes smoothly in the direction opposite from your head movement so you never lose
focus. Did you ever swing a bat, swat a mosquito, or jump rope? Part of the midbrain
and its connections to the forebrain allowed you to produce those movements
smoothly. When a car backfires, causing you to reflexively turn your head and look in
the direction of the sound, it is again the midbrain at work. Together, the midbrain and
parts of the hindbrain other than the cerebellum are called the brainstem.
The Forebrain
midbrain A small region between the
hindbrain and the forebrain that,
among other things, helps produce
smooth movements.
forebrain The part of the brain
responsible for the most complex
aspects of behavior and mental life.
thalamus A forebrain structure that
relays messages from most sense organs
to higher brain areas.
hypothalamus A forebrain structure
that regulates hunger, thirst, and sex
drives, with many connections to and
from the autonomic nervous system
and other parts of the brain.
amygdala A forebrain structure that
links information from various systems
and plays a role in emotions.
In humans, the forebrain controls the most complex aspects of behavior and mental
life. It completely covers the rest of the brain. The outer surface of the forebrain is
called the cerebral cortex. Figure 2.9 shows some structures of the forebrain.
Two structures deep within the forebrain, the hypothalamus and the thalamus, help
operate basic drives, emotion, and sensation. The thalamus acts as a relay station for
pain and sense-organ signals (except smell) from the body to the upper levels of the
brain. The thalamus also processes and makes sense of these signals. The hypothalamus lies under the thalamus (hypo means “under”) and helps regulate hunger, thirst,
and sex drives. The hypothalamus is well connected to the autonomic nervous system
and to other parts of the brain. Damage to parts of the hypothalamus upsets normal
appetite, thirst, and sexual behavior.
Can you set an “internal alarm clock” to wake up in the morning at whatever time
you want? If you can, it is with the help of a remarkable part of your hypothalamus,
called the suprachiasmatic nuclei, that contains the brain’s own clock. The suprachiasmatic (pronounced “soo-pra-kye-as-MAT-ik”) nuclei operate on approximately a
twenty-four-hour cycle, controlling daily biological rhythms such as waking and sleeping, as well as cycles of body temperature. Studies of the suprachiasmatic nuclei in animals suggest that having different night or morning energy times is biological and stable throughout a lifetime (Cofer et al., 1992). In humans, such differences may make
some of us “morning people” and others “night people.”
Other parts of the forebrain, especially the amygdala (pronounced “ah-MIG-duhluh”) and the hippocampus, help to regulate memory and emotion. The amygdala links
different kinds of sensory information in memory, such as the shape and feel of objects
(Murray & Mishkin, 1985). If you close your eyes and pick up an object, your amygdala helps you recognize it. The amygdala also plays a role in fear and other emotions