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

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 Si. Results suggest that the deviant gating ratio in schizophrenia is a con sequence of a complex alteration in the processing of incoming information that cannot be attributed to impaired gating alone. (C) 2011 Elsevier Inc. All rights reserved.