Cross axis vestibulo-ocular reflex induced by pursuit training in alert monkeys

We examined the effect of conflicting vestibular and smooth pursuit information on the vestibulo-ocular reflex (VOR) in alert monkeys. Sinusoidal whole body rotation was applied either in the pitch or yaw plane while presenting a target spot that moved orthogonally to the rotation plane. The monkeys were rewarded for tracking the spot and eye movements induced by rotation alone were examined every 15-30 min in complete darkness. Orthogonal eye movement responses to rotation were not observed before training but appeared after about 30 min of training. The gains (eye/chair) of the orthogonal component increased up to 0.2 after 1-2 h and were largest at the training frequency and approximately in phase with the stimulus; phase advanced at lower frequencies and lagged at higher frequencies. Amplitude tuning was also demonstrated when examined using different amplitudes at a constant frequency after training. Two hours of training to fixate an earth-stationary spot projected onto a patterned visual background that moved orthogonally to the rotation plane during rotation, did not induce a cross axis response. These results indicate that pursuit training during VOR is effective in inducing cross-axis eye movement responses that are tuned to the metrics of the training stimulus.