Chapter 45. The Limbic System

1. The limbic system is a group of neural structures located above the brainstem but below the cerebral cortex. These structures wrap around the thalamus.

2. The most important components of the limbic system are the hypothalamus, the hippocampus, and the amygdala. These structures are involved in emotions (such as fear and aggression) and drives (such as hunger, thirst, and sexual urges).

3. Although the pituitary gland is part of the endocrine system, not the limbic system, it is included here because it is tightly controlled by the hypothalamus, and forms a link between the limbic system and the body’s emotional responses.

4. Let’s look more closely at the three most important limbic system structures. The hypothalamus monitors the body’s internal status, watching for changes in temperature, fluid or oxygen level, or energy storage. When any of these falls outside the normal range, the hypothalamus motivates an appropriate behavior (such as eating, drinking, or seeking warmth) to correct the problem.

5. The hippocampus seems to be essential for forming new permanent memories. Individuals with damage to the hippocampus can think and perceive the world normally, but can’t store new factual information in memory.

6. Finally, the amygdala is involved in emotions connected to survival—primarily fear and anger or aggression. Neural activity in the amygdala increases when a person becomes frightened at the sight of a spider or a snake, or even when viewing human faces that display an angry or fearful expression.