Differential effects of inferior olive lesion on vestibulo-ocular and optokinetic motor learning.

The combined operation of optokinetic reflex (OKR) and vestibular-ocular reflex (VOR) is essential for image stability during self-motion. Retinal slip signals, which provide neural substrate for OKR and VOR plasticity, are delivered to the inferior olive. Although it has been assumed that the neural circuitry and mechanisms underlying OKR and VOR plasticity are shared, differential role of the inferior olive in the plasticity of OKR and VOR has not been clearly established. To investigate the differential effect of inferior olive lesion on OKR and VOR plasticity, we examined the change of OKR and VOR gains after gain-up and gain-down VOR training. The results demonstrated that inferior olive-lesion differentially affected cerebellum-dependent motor learning. In control mice, OKR gain increased after both gain-up and gain-down VOR training, and VOR gain increased after gain-up VOR training and decreased after gain-down VOR training. In inferior olive-lesioned mice, OKR gain decreased after both gain-up and gain-down VOR training, and while VOR gain did not significantly change after gain-up VOR training, VOR gain decreased after gain-down VOR training. We suggest that multiple mechanisms of plasticity are differentially involved in VOR and OKR adaptation, and gain-up and gain-down VOR learning rely on different plasticity mechanisms.