Reduced Early Auditory Evoked Gamma-Band Response in Patients with Schizophrenia

BackgroundThere is growing evidence for abnormalities of certain γ-aminobutyric acid (GABA)-ergic interneurons and their interaction with glutamatergic pyramidal cells in schizophrenia. These interneurons are critically involved in generating neural activity in the γ-band (30–100 Hz) of the electroencephalogram. One example of such γ oscillations is the early auditory evoked γ-band response (GBR). Although auditory processing is obviously disturbed in schizophrenia, there is no direct evidence providing a reduced early auditory evoked GBR so far. We addressed two questions: 1) Is the early auditory evoked GBR decreased regarding power and phase-locking in schizophrenic patients?; and 2) Is this possible decrease a result of reduced activity in the auditory cortex and/or the anterior cingulate cortex (ACC), which were identified as sources of the GBR previously?MethodsWe investigated the early auditory evoked GBR and its sources in the ACC and the auditory cortex in 90 medicated patients with schizophrenia and in age-, gender-, and education-matched healthy control subjects with an auditory reaction task.ResultsPatients with schizophrenia showed a significant reduction of power and phase-locking of the early auditory evoked GBR. This effect was due to a reduced activity in the auditory cortex and the ACC/medial frontal gyrus region (low-resolution brain electromagnetic tomography analysis).ConclusionsGenerally, these findings are in line with earlier reports on the impaired ability of schizophrenic patients in generating γ activity. In addition, this is the first study to demonstrate disturbance of γ activity in auditory processing as assessed by the early auditory GBR power.