Effects of lesions of globus pallidus on species-typical display behavior of squirrel monkeys.

In a study of brain mechanisms underlying species-typical communication, systematic testing has been conducted on the effects of cerebral lesions on the mirror display of squirrel monkeys. The mirror display is a highly predictable variation of a naturally occurring display used by male squirrel monkeys in a show of aggression, in courtship and in greeting. Of the 5 features of the display, vocalization, thigh-spreading and forward thrusts of the erect phallus are the major and most regularly occurring manifestations, constituting the so-called trump display. Testing has been performed on more than 100 animals with lesions in various structures of the brain. The present report describes the positive effects of electro-coagulation of certain parts of the globus pallidus. Lesions of the medial segment have resulted in an enduring elimination or fragmentation of the trump display. Recovery of the display may occur with lesions predominantly involving the external segment, while destruction of the caudalmost pallidum is without effect. A variety of evidence indicates that the behavioral changes are not due to a deterioration of health, motor disabilities, seasonal factors or motivation. When weighed against the negative or transitory effects of lesions of numerous other structures of the brain, the present findings support the hypothesis that the striatal complex plays a basic role in the organized expression of species-typical behavior.