Behavioral inhibition induced by pallidal stimulation in monkeys

To study possible inhibitory functions of the globus pallidus, nine rhesus monkeys were equipped with intracerebral electrodes, radio stimulators, and telerecorders of mobility. Results were: (a) Under restraint, pallidal stimulation induced contralateral head turning, and/or flexion of the contralateral arm without evoking detectable changes in electrical activity of the brain, emotionality, or reactivity to food or threats. (b) A single 5-sec radio stimulation of the pallidum in the monkey, free and alone in a cage, produced discrete motor responses which did not disturb spontaneous behavior or taking of pellets, but inhibitory effects appeared when repeated feedback or programmed stimulations were used. (c) Stimulation of the pallidum in the dominant partner of a caged pair, triggered automatically by its mobility, changed the social status of both animals, inhibiting signs of dominance in the stimulated monkey and correspondingly increasing the social rank of the nonstimulated animal. (d) Effects of stimulation of the pallidum in the same animal depended on its hierarchical status. When dominant, it became submissive, while only minor stimulation effects were observed when it was the submissive partner. (e) It is suggested that the pallidum has an integrative role in the relation between the animal's motivational state and its environment.