Backward masking in unmedicated schizophrenic patients in psychotic remission: possible reflection of aberrant cortical oscillation.

Abstract

Patients with schizophrenia consistently show performance deficits on measures of visual backward masking, but the nature of these deficits is not well understood. Performance deficits on backward masking tasks may indicate an underlying predisposition instead of the presence of illness, because deficits are present in unaffected first-degree relatives. Performance deficits in remitted patients would constitute converging support for this hypothesis. Eleven patients with recent-onset schizophrenia who were in a period of no medication use during remission of psychosis were compared with a matched normal group on three visual masking conditions. These conditions included target identification tasks with a high-energy mask, a low-energy mask, and a blurred target. Patients in psychotic remission showed significant deficits across all conditions. In addition, trend analyses revealed significant group differences in the shape of the masking functions: the comparison group showed an oscillating performance pattern across all masking conditions, whereas the patients did not exhibit this pattern on any condition. These data from patients in well-documented psychotic remission add converging support for the hypothesis that deficits on backward masking procedures are indicators of vulnerability to schizophrenia. Because visual masking procedures may reflect underlying neural oscillations of 30 to 70 Hz in the visual cortex, the pattern of results is consistent with the theory that visual masking deficits in schizophrenia stem from an underlying failure to establish cortical oscillations.