Detection of tracking errors by visual climbing fiber inputs to monkey cerebellar flocculus during pursuit eye movements.

The activity of cerebellar Purkinje cells was monitored in alert monkeys during visually guided smooth pursuit eye movements. The climbing fiber input evokes 'complex-spikes' which show increased firing during the contralateral phase of sinusoidal pursuit. 'Complex-spike triggered averaging' revealed that the increased firing is a visual response to the retina slip which results from inaccurate tracking. The complex-spikes in turn cause a transient reduction in the simple-spike pursuit command signal that emanates from the flocculus and this may contribute to the corrective eye movement. We postulate that the detection (and possibly the correction) of small errors in motor performance may be a general function of climbing fiber inputs to the cerebellum.