Evoked and induced oscillatory activity contributes to abnormal auditory sensory gating in schizophrenia

Abstract

The ratio of magnetoencephalogram-recorded brain responses occurring 50 ms after paired clicks (S2-evoked M50/S1-evoked M50) serves as a measure of sensory gating. An abnormally large ratio is commonly found in schizophrenia. Whether this abnormality indicates impaired gating is debated. Using event-related oscillations the present study sought to elucidate processes contributing to the phenomenon of altered M50 gating ratio. Schizophrenia inpatients (n=50) showed the expected large M50 gating ratio relative to 48 healthy controls, which correlated with less induced frontally generated activity in the 10–15 Hz frequency band starting 200 ms before the onset of S2. Patients also produced smaller alpha (8–12 Hz) and gamma (60–80 Hz) responses to S1. Results suggest that the deviant gating ratio in schizophrenia is a consequence of a complex alteration in the processing of incoming information that cannot be attributed to impaired gating alone.