Closed-loop optogenetic perturbation of macaque oculomotor cerebellum: evidence for an internal saccade model.

Theory and experiment suggest that saccade production involves an internal model of oculomotor mechanics that resides inside the cerebellum. How cerebellar neurons implement this model is poorly understood. To shed light on this issue, we briefly stimulated P-cells in the OMV optogenetically during saccades and examined the resultant movement deviations. Stimulation of the contralateral OMV affected saccade dynamics at short latency, suggesting that the contralateral OMV is part of the feedforward circuit that produces the saccade motor command. In contrast, perturbation of the ipsilateral OMV affected saccade dynamics at a longer latency; it prolonged the saccade deceleration phase, leading to hypermetria. This dysmetria is consistent with perturbation of the eye displacement integrator in the feedback loop of the saccade generator.