Abnormal visual-vestibular interaction and smooth pursuit tracking in psychosis: implications for cerebellar involvement.

The vestibulo-ocular response to caloric irrigation and the effect of vestibular activation on eye movements were examined during light and dark testing conditions--the latter to assess these measures under conditions attenuating possible cerebellar-vestibular interaction present in the light-adapting condition. Subjects were psychiatric patients (23 actively-ill psychotic patients and 23 remitted psychotic patients) and normal controls (23 with no history of psychiatric illness). Standardized clinical electronystagmographic procedures were used, together with electrographic measures to assess visual fixation and level of arousal. During the light condition previous findings of impaired smooth pursuit tracking and reduced fixation suppression in actively psychotic patients were replicated. These patients also exhibited hyperresponsive vestibulo-ocular responses. Remitted patients' performance levels on test measures fell between those of controls and actively-ill patients on the majority of response measures. However, remitted patients were found to have impaired smooth pursuit tracking and failure of fixation suppression relative to controls. The dark testing condition effected a normalization of several patient-control differences, including smooth pursuit tracking and the elimination of vestibular hyperresponsiveness. In many respects the present results parallel findings of eye movement aberrations in cerebellar patients. These similarities include evidence of an intact but hyperresponsive vestibular system, the normalization of previously disordered pursuit tracking during dark-testing, the failure of fixation suppression, and the decrease in this measure during dark conditions. These findings suggest that cerebellar dysfunction may contribute to irregularities in smooth pursuit tracking and fixation suppression found in psychotic patients.