The Cerebral Cortex

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FIGURE
Chapter 2 Biology and Behavior
2.9
Major Structures of the Forebrain
The structures of the forebrain are covered by an outer “bark” known as the
cerebral cortex. This diagram shows some
of the structures that lie within the forebrain. The amygdala, the hippocampus,
and portions of the cerebral cortex are
part of the limbic system.
Cerebral
cortex
Corpus
callosum
Thalamus
Hypothalamus
Amygdala
Hippocampus
(LeDoux, 1995; Whalen, 1998), connecting emotion to sensation. People who suffer
from posttraumatic stress disorder have unusual amygdala activity (Pitman, Shin, &
Rauch, 2001). The amygdala, hippocampus, and some portions of the cerebral cortex
are part of a group of brain structures called the limbic system, which is activated when
emotions are being generated.
The hippocampus also helps you form new memories. In one case, a patient known
as R.B. suffered a stroke (an interruption of blood flow to the brain) that damaged only
his hippocampus. Although his intelligence remained above average and he could recall
old memories, he was almost totally unable to build new memories (Squire, 1986).
Damage to the hippocampus within a day of a mildly painful event seems to erase
memories of the experience. However, if the damage occurs several days after the event,
the memory remains. It seems that memories are not permanently stored in the hippocampus but instead are transferred from there to somewhere else in the brain.
The hippocampus becomes smaller with age, and research shows that this shrinkage
relates to the declining memory function that many elderly people experience (Golomb
et al., 1996). On average, the hippocampus of a person with Alzheimer’s disease has
been found to be 40 percent smaller than that of a person without the disease.
Alzheimer’s disease is a major cause of senile dementia, which involves the decay of
cognitive capabilities. About 10 percent of people over age sixty-five and 47 percent
of people over eighty-five suffer from this disease (Kukull et al., 2002; U.S. Department
of Health and Human Services, 2001a). The financial cost of Alzheimer’s disease is more
than $100 billion a year in the United States alone (U.S. Department of Health and
Human Services, 2001a). The cost in human suffering is incalculable.
The Cerebral Cortex
hippocampus A forebrain structure
associated with the formation of new
memories.
cerebral cortex The outer surface of
the forebrain.
corpus callosum A bundle of fibers
that connects the left and right cerebral
hemispheres.
On the surface of the forebrain is the cerebral cortex. The total area of the cerebral
cortex is one to two square feet, but it fits into the skull because it is somewhat wrinkled and folded. You can wad up a T-shirt and fit it into a small bowl in much the same
way. The cerebral cortex is much larger in humans than in most other animals (dolphins
are an exception). It analyzes information from all the senses and controls voluntary
movement, abstract thinking, and the other most complex aspects of our behavior and
mental processes. The cerebral cortex looks somewhat round, with a long groove down
the middle creating two halves, called cerebral hemispheres. The corpus callosum, a
massive bundle of more than a million fibers, connects the two hemispheres.