The Cerebral Cortex
64 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.