Role of dopamine in the primate caudate nucleus in reward modulation of saccades

Expected reward impacts behavior and neuronal activity in brain areas involved in sensorimotor processes. However, where and how reward signals affect sensorimotor signals is unclear. Here, we show evidence that reward-dependent modulation of behavior depends on normal dopamine transmission in the striatum. Monkeys performed a visually guided saccade task in which expected reward gain was different depending on the position of the target. Saccadic reaction times were reliably shorter on large-reward trials than on small-reward trials. When position-reward contingency was switched, the reaction time difference changed rapidly. Injecting dopamine D-1 antagonist into the caudate significantly attenuated the reward- dependent saccadic reaction time changes. Conversely, injecting D-2 antagonist into the same region enhanced the reward-dependent changes. These results suggest that reward-dependent changes in saccadic eye movements depend partly on dopaminergic modulation of neuronal activity in the caudate nucleus.