Neuronal responses in MST reflect the post-saccadic enhancement of short-latency ocular following responses

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Movements of the visual scene evoke short latency ocular following responses (OFRs) in monkeys that are mediated at least in part by the medial superior temporal area of the cortex (MST). It is known that the sensitivity of the OFR to motion is transiently enhanced immediately after a saccade and this post-saccadic enhancement is largely secondary to visual reafference during the antecedent saccade. As part of an investigation of the neural basis of this post-saccadic enhancement, we examined the dependence of OFR-related neuronal activity in MST on the post-saccadic delay interval in alert monkeys (Macaca fuscata). Large-field motion stimuli were applied either 50 or 150 ms after a centering saccade and response measures were based on the initial (open-loop) changes in (a) eye position and (b) discharge rate. Of the 67% of MST neurons whose OFR-related activity showed significant dependence on the post-saccadic delay, 91% mirrored the OFR, showing higher sensitivity to motion at the shorter post-saccadic delay interval. However, the sensitivity of OFR-related neurons in MST to post-saccadic delay varied considerably from cell to cell and, on average, was 79.6% of that shown by the OFR. We suggest that this enhanced OFR-related activity in the wake of a saccade is causally linked to the visually based post-saccadic enhancement of the OFR.

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