Eye tracking abnormalities in schizophrenia: evidence for dysfunction in the frontal eye fields.

BACKGROUND: Eye tracking deficits are robust abnormalities in schizophrenia, but the neurobiological disturbance underlying these deficits is not known. METHODS: To clarify the pathophysiology of eye tracking disturbances in schizophrenia, we tested 12 first-episode treatment-naive schizophrenic patients and 10 matched healthy individuals on foveofugal and foveopetal step-ramp pursuit tasks. RESULTS: On foveopetal tasks, the initiation of pursuit eye movements was delayed in schizophrenic patients, and their steady-state pursuit gain was reduced particularly at slower target speeds (8 and 16 deg/sec). In foveofugal step-ramp tasks, their primary catch-up saccades were normal in latency and accuracy, but their postsaccadic pursuit in the first 100 msec after the primary catch-up saccade was significantly reduced even relative to their slow steady-state pursuit, especially during and immediately after an acute episode of illness. CONCLUSIONS: These observations indicate that motion-sensitive areas in posterior temporal cortex provide sufficiently intact information about moving targets to guide accurate catch-up saccades, but that the sensory processing of motion information is not being used effectively for pursuit eye movements. Low-gain pursuit after the early stage of pursuit initiation suggests that the use of extraretinal signals about target motion (e.g., anticipatory prediction) only partially compensates for this deficit. The pattern of low-gain pursuit, impaired pursuit initiation, and intact processing of motion information for catch-up saccades but not pursuit eye movements, was consistent in the schizophrenic patients tested at five time points over a 2-year follow-up period, and implicates the frontal eye fields or their efferent or afferent pathways in the pathophysiology of eye tracking abnormalities in schizophrenia.