Aberrant EEG responses to gamma-frequency visual stimulation in schizophrenia

Disturbance in the integration of visual information is one of the hallmarks of schizophrenia In the spatial domain visual integration is compromised resulting in impaired perceptual grouping and contour integration In the time domain in contrast visual integration is enhanced as manifested by Increased backward masking and lower ability of patients to detect successively presented visual stimuli as asynchronous There is much evidence that integrative processes in the brain are supported by dynamic synchronization or phase-locking of neural firing In particular synchrony in the gamma band (>30 Hz) has been related to local visual information binding whereas synchrony in lower frequencies has been linked to global-scale integration We recorded EEG signals evoked by steady-state gamma-frequency (40 Hz) photic stimulation in order to directly test the phase-locking of neural responses in schizophrenia Compared with healthy control subjects patients showed higher phase-locking of early evoked activity in the gamma band (3644 Hz) over the posterior cortex but lower phase-locking in theta (4-8 Hz) alpha (8-13 Hz) and beta (13-24 Hz) frequencies over the anterior cortex. Phase locking of evoked responses separated schizophrenia and control subjects with accuracy of 86% This result suggests that schizophrenia is associated with an enhanced early low-level integration in the visual cortex but a deficient high-level integration of visual information within the brain global workspace (C) 2010 Elsevier B V All rights reserved