Saccade-related inhibitory burst neurons (IBNs) alter their activity in relation to amplitude-decreasing adaptation in the monkey.

Abstract

Saccade accuracy, a prerequisite for efficient collection of visual information, is maintained by an adaptive mechanism that modifies saccade amplitude. Previous studies show that adapting saccade amplitude induces correlated changes in neuronal activity in the cerebellar fastigial oculomotor region (FOR). In the present study we recorded the activity of saccade-related inhibitory burst neurons, IBNs, which may relay FOR signals to motoneurons. We examined if IBN activity changed during adaptation and could contribute to it. We tested 44 IBNs during amplitude-decreasing adaptation of contraversive (off-direction) saccades. Thirty-seven IBNs fired, at least occasionally, for off-direction saccades. The remaining 7 exhibited no spikes for off-direction saccades. We used intrasaccadic target steps to adapt the gain of saccades to 10° target steps in the off-direction. Many IBNs which exhibited off-direction spikes showed an increasing number of spikes (23/37), a shortening burst lag (13/37) or both (12/37) as adaptation progressed. IBNs with no off-direction spikes showed no spike activity after adaptation. These results suggest that the adaptation-related changes in IBN activity decrease the size of contraversive saccades by decreasing the size of the burst in motoneurons. [J Physiol Sci. 2006;56 Suppl:S187]