Enhanced modulation of neuronal activity during antisaccades in the primate globus pallidus.

The antisaccade task has been widely used to investigate the neural mechanisms underlying volitional movement control. In this task, subjects suppress reflexive saccades to the sudden appearance of peripheral visual stimuli (prosaccades) and generate a saccade in the opposite direction. Recent imaging studies suggest that the globus pallidus (GP) is involved in the generation of antisaccades. To understand the roles of the GP, we examined single neuron activity and the effects of local inactivation. Monkeys were trained to make either a pro- or antisaccade according to prior instruction provided by the color of the fixation point in each trial. Among 119 saccade-related neurons, 55% showed increased firing rates associated with saccades, whereas the remaining neurons showed decreased firing rates. For both populations of neurons, the activity modulation was enhanced during the preparation and execution of antisaccades, as compared with prosaccades. Inactivation of the recording sites in the external segment of the GP resulted in an increase in the number of error trials in the antisaccade tasks, suggesting that signals in the GP may play roles in suppressing inadequate prosaccades in the task. Signals in the GP might regulate eye movements through the nigro-collicular descending circuitry and through the basal ganglia-thalamocortical pathways.