OPEN-LOOP SIMULATIONS OF THE PRIMATE SACCADIC SYSTEM USING BURST CELLDISCHARGE FROM THE SUPERIOR COLLICULUS

Saccade-related burst neurons (SRBNs) in the monkey superior colliculu s (SC) have been hypothesized to provide the brainstem saccadic burst generator with the dynamic error signal and the movement initiating tr igger signal. To test this claim, we performed two sets of open-loop s imulations on a burst generator model with the local feedback disconne cted using experimentally obtained SRBN activity as both the driving a nd trigger signal inputs to the model. First, using neural data obtain ed from cells located near the middle of the rostral to caudal extent of the SC, the internal parameters of the model were optimized by mean s of a stochastic hill-climbing algorithm to produce an intermediate-s ized saccade. The parameter values obtained from the optimization were then fixed and additional simulations were done using the experimenta l data from rostral collicular neurons (small saccades) and from more caudal neurons (large saccades); the model generated realistic saccade s, matching both position and velocity profiles of real saccades to th e centers of the movement fields of all these cells. Second, the model was driven by SRBN activity affiliated with interrupted saccades, the resumed eye movements observed following electrical stimulation of th e omnipause region. Once again, the model produced eye movements that closely resembled the interrupted saccades produced by such simulation s, but minor readjustment of parameters reflecting the weight of the p rojection of the trigger signal was required. Our study demonstrates t hat a model of the burst generator produces reasonably realistic sacca des when driven with actual samples of SRBN discharges.