Pursuit eye movement dysfunction in schizophrenia: Characteristics of oculomotor disturbance and diagnostic specificity

Abstract

Abnormalities of visual pursuit are among the most robust psychobiological abnormalities observed in schizophrenia. These abnormalities are present and associated with schizotypal characteristics in relatives of affected probands, suggesting that the abnormality is a familial marker for the illness. Yet, the diagnostic specificity of the abnormality has not been well studied, and the neurophysiologic significance of the abnormality is not understood. Therefore, we studied pursuit performance in 101 schizophrenic inpatients (19 never medicated), 18 unmedicated manic inpatients (DSM-III-R diagnoses), and 46 age and sex-matched normal controls. Patients visually tracked a cursor oscillating at 0.4 Hz for 30 second trials in a block room. Performance was quantified by assessing the relative velocity of pursuit eye movements (gain), and the frequency of two forms of intrusive saccades that interrupt pursuit: square wave jerks (SWJ) and anticipatory saccades. Pursuit gain of both manic and schizophrenic patients was significantly lower than in normals, but the impairments were of a similar order of magnitude. It was expected that schizophrenics would show more SWJ, as is the case in several neurological disorders involving disease of the frontal lobe or basal ganglia where there is a failure to suppress irrelevant saccades. Contrary to this expectation, schizophrenic patients demonstrated fewer SWJ than the other groups. The sub-sample of 19 never-medicated acutely-disturbed schizophrenics had higher leftward than rightward pursuit velocity and more rightward SWJ, suggesting greater relative left hemisphere activation in these patients. Manic patients demonstrated asignificant increase above normal levels in anticipatory saccades, while schizophrenic patients did not. Schizophrenic patients with fewer SWJ had poorer adult social adjustment and earlier onset of illness, and more perseverative errors on the Wisconsin Card Sort, poorer verbal list learning, and poorer perception of line orientation. Thus, reduced SWJ may identify a group of more severely affected cases. In schizophrenics, low gain was unrelated to symptom indices, but was related to impairments on cognitive tests Trails B, Judgement of Line Orientation (JLOT) and Digit Span. The results indicate that different forms of pursuit disturbance occur in manic and schizophrenic patients, and that in schizophrenics pursuit impairments were associated with neuropsychological dysfunctions. Lateralized disturbances of pursuit suggesting greater relative left hemisphere activation occur in the acute phase of illness, consistent with findings from studies that have used other cognitive and neuroimaging assessment strategies.