Pursuit tracking impairments in schizophrenia and mood disorders: step-ramp studies with unmedicated patients

Background: Eye tracking abnormalities are highly prevalent in schizophrenia, and are among the most promising phenotypic familial markers for the disorder. The neurophysiologic mechanisms underlying these disturbances and their diagnostic specificity for schizophrenia are not yet well characterized. Methods: This study assessed eye tracking deficits using foveopetal and foveofugal step-ramp tasks (ramps moving toward and away from central fixation after an initial step respectively) across a range of target velocities in anti-psychotic-naive schizophrenia patients, previously treated but currently unmedicated chronic schizophrenia patients, unmedicated patients with either bipolar or unipolar mood disorders, and healthy volunteers. Results: All patient groups demonstrated reduced pursuit gain in open loop and closed loop visual tracking conditions. There were no significant group differences in the latency or accuracy of catch-up saccades on foveofugal ramp tasks. Conclusions: These findings indicate that open and closed loop pursuit eye movements are impaired during acute episodes of schizophrenia and mood disorders. The intact accuracy of saccades to moving targets in all patient groups indicates that an adequate representation of motion information is available to the saccade system. Therefore, pursuit disturbances in mood disorders and schizophrenia seem to result, at least in part, from a disturbance in sensorimotor integration in the pursuit system after the initial extraction of sensory motion information. No eye movement abnormalities observed during performance of step ramp tasks were specific to schizophrenia.