Functional role of pallidum revealed by its electrical stimulation and coagulation in unanesthetized squirrel monkeys

Pallidum-induced direction-specific movements in squirrel monkeys were studied with stimulation or coagulation of this brain structure. The reactions to pallidum externum stimulation were small rapid and phasic head movements, mainly towards the contralateral side. Stimulation of pallidum internum produced a contralateral turning of the head. After high-frequency coagulation of one pallidum, the direction of unrestrained locomotion was exclusively to the lesioned side. Lesions that included the most medial parts of the pallidum produced a continuous ipsiversive circling behavior. These results demonstrate the crucial role of the pallidum in directing contraversive turning movements around the vertical axis of the body.