Abstract
Saccades are rapid eye movements that acquire a visual target in the fovea. Because the fovea is small, saccades must be very accurate. Saccade accuracy is ensured by a learning mechanism, called saccade adaptation, which is induced by visual error at movement end. Very little is known about central pathways that bring error signals for saccade adaptation. Here we show that microstimulation of the medial part of the midbrain tegmentum created learning signals for saccade adaptation in monkeys. Weak electrical stimuli delivered ∼200 ms after targeting saccades in one horizontal direction produced gradual and marked changes in saccade gain. The spatial and temporal characteristics of the produced changes were similar to those of adaptation induced by real visual error that was created by stepping the target during saccades. When stimulation was applied after saccades in two different directions, endpoints of these saccades gradually shifted in the same direction in two dimensions. Thus microstimulation created learning signals that dictated the direction of "adaptive" shift in movement endpoints. Our findings suggest that the error signals for saccade adaptation are conveyed in a pathway that courses in the midbrain tegmentum. [J Physiol Sci. 2007;57 Suppl:S161]
