EYE-MOVEMENTS IN MONKEYS WITH LOCAL DOPAMINE DEPLETION IN THE CAUDATE-NUCLEUS .2. DEFICITS IN VOLUNTARY SACCADES

Unilateral infusion of MPTP into the monkey caudate nucleus produced d eficits in task-specific saccades, in addition to the deficits in spon taneous eye movements (preceding article). We trained three monkeys to perform two kinds of saccade tasks: (1) saccade task for eliciting vi sually guided saccades and (2) delayed saccade task for eliciting memo ry-guided saccades. After the MPTP infusion, dopaminergic function, es timated by tyrosine hydroxylase (TH) immunoreactivity, was shown to be decreased locally around the infusion site at the head-body junction of the caudate. We found that the deficits were prominent in the sacca des directed to the side contralateral to the infusion (contralateral saccades). Memory-guided saccades were sometimes misdirected to the ip silateral side even when the cue stimulus was presented on the contral ateral side. Among the parameters of saccades, a selective change was found in the saccade latency: the latency was prolonged consistently i n contralateral memory-guided saccades. The amplitude and velocity of saccades decreased in contralateral saccades, either memory guided or visually guided. The duration of saccades tended to increase in visual ly-guided saccades and memory-guided saccades, in both directions. Onl y one monkey, in which the decrease in TH activity included a large pa rt of the putamen and the head of the caudate, showed prolongation of manual reaction time for lever release.