Plastic properties of the vestibulo-ocular reflex in olivo-ponto-cerebellar atrophy.

Disorders in vestibulo-ocular functions were studied in 4 patients with olivo-ponto-cerebellar atrophy (OPCA). The phenomenon of habituation, considered as a plastic property of the vestibulo-ocular reflex (VOR), was explored with a behavioural paradigm in these patients. When subjected to the habituation paradigm all patients presented a modified response opposite to that observed in normal subjects. The role played by the cerebellum in relation to VOR plasticity--well known in different experimental models--is analyzed. The hypothesis of a modification of the cerebellum's inhibitory action on vestibular nuclei neurons is put forward to explain the inversion of the VOR habituation phenomenon in these patients.