Neurophysiologic mechanisms of attention deficits in schizophrenia.

Background: Despite advances in the pharmacologic treatment of schizophrenia, the neurophysiologic mechanism(s) of disordered attention in schizophrenia remain elusive.

Objective: The goal of the present study was to assess specific components of attention, including disengagement, movement, re-engagement, and the inhibitory processes involved their control.

Methods: Thirteen chronic schizophrenics from the inpatient and outpatient units of the Veterans Administration Medical Center (New Orleans, LA) and thirteen normal control subjects were administered a saccadic eye movements task. Saccade latency was measured in the presence of contra-lateral distracter stimuli that preceded the target onset (Distracter-before), followed the target onset (Distracter - after) or in the absence of a distracter (No-distracter). In order to assess the interactive process of fixation disengagement and target selection, fixation was either offset before the target (Gap) or it remained on in the presence of the target (Overlap).

Results: Repeated measures analysis of variance revealed that saccadic latency in patients with schizophrenia is prolonged to a greater extent than in normal control subjects in the presence of distracter stimuli. Patients with schizophrenia are also characterized by a greater percentage of error saccades directed to the distracter, and require a longer latency to "issue" corrective saccades following error saccades.

Conclusions: The findings suggest that patients with schizophrenia are required to invoke volitional control under distracter conditions, whereas normal control subjects require minimal volitional control. The results are interpreted in terms of the inhibitory mechanisms that regulate attention.