The effect of changing basal ganglia activity with electrical stimulation in and around the globus pallidus (GP) was studied in monkeys trained to make rapid arm-reaching movements to a visual target in a reaction time. As was the case following kainic acid (KA) lesions of the globus pallidus (30), stimulation changes movement times (MT) without affecting the pattern of sequential activation of muscles involved in the task or, in most cases, the reaction times (RT). Stimulation in the ventrolateral internal segment of the globus pallidus [GP(i)] or in the ansa lenticularis reduced movement times, whereas stimulation at many sites in the external pallidal segment [GP(e)], dorsal GP(i), and putamen increased movement times for the contralateral arm. These results are consistent with the hypothesis that arm movements are speeded up when the critical output of GP(i) is increased and arm movements are slowed down when critical GP(i) output is reduced, either by an inhibitory process (via stimulation-induced activation of inhibitory elements presynaptic to GI(i)) or by destroying GP(i) neurons (via kainic acid). The influence of the basal ganglia on the scaling of electromyographic (EMG) amplitude, as opposed to the spatiotemporal organization of EMG activation, is discussed.
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