AMYGDALA (Amygdaloid Complex)

A brain structure located beneath the frontal lobe and involved in the control of emotion and motivation.The amygdala is a part of the “old brain” or rhinencephalon, which is wholly devoted to the sense of smell in lower animals. But since this sense plays a smaller role in the behavior of human beings, the area has apparently become a center for dealing with emotional experience.Research on the amygdala has been largely carried out on animals. It apparently has an excitatory effect on anger and an inhibitory effect on sexuality. When portions of the amygdala were cut, cats and monkeys became extremely placid and docile (Schreiner and Kling, 1956; Smith, 1950). After amygdalec- tomy (complete destruction) wild animals ceased to bite and scratch even when handled or pinched; a lynx, for example, became as tame as a kitten (Schreiner and Kling, 1953). Other experiments have shown that the relationship of animals to each other is also changed when lesions are made in this structure—for example, dominant male monkeys became extremely submissive after the operation. (Rosvold et al., 1954)As expected, electrical stimulation of one part of the area produced rage, but stimulation of another part was found to elicit fearlike behavior. It is believed that the amygdala and the hypothalamus operate together in all these reactions, although the exact relationship between these structures is not wholly clear at present.The inhibitory effect on sexuality was demonstrated by making lesions in parts of the amygdala. Eliminating these parts removed the inhibiting effect and as a result female cats were more easily aroused by the male, and male cats made advances not only to female cats but to males and to other animals such as hens (Schreiner and Kling, 1953, 1954). For reasons unknown, the same lesions made in immature animals did not affect sexual response when theygrew to adulthood (Kling, 1962).