Gamma frequency-range abnormalities to auditory stimulation in schizophrenia

Background: Basic science studies at the neuronal systems level have indica ted that gamma-range (30-50 Hz) neural synchronization may be a key mechani sm of information processing in neural networks, reflecting integration of various features of an object. Furthermore, gamma-range synchronization is thought to depend on the glutamatergically mediated interplay between excit atory projection neurons and inhibitory neurons utilizing gamma-aminobutyri c acid (GABA), which postmortem studies suggest may be abnormal in schizoph renia. We therefore tested whether auditory neural networks in patients wit h schizophrenia could support gamma-range synchronization. Methods: Synchronization of the electroencephalogram (EEG) to different rat es (20-40 Hz) of auditory stimulation was recorded from 15 patients with sc hizophrenia and 15 sex-, age-, and handedness-matched control subjects. The EEG power at each stimulation frequency was compared between groups, The t ime course of the phase relationship between each stimulus and EEG peak was also evaluated for gamma-range (40 Hz) stimulation. Results: Schizophrenic patients showed reduced EEG power at 40 Hz, but not at lower frequencies of stimulation. In addition, schizophrenic patients sh owed delayed onset of phase synchronization and delayed desynchronization t o the click train. Conclusions: These data provide new information on selective deficits in ea rly-stage sensory processing in schizophrenia, a failure to support the ent rainment of intrinsic gamma-frequency oscillators. The reduced EEG power at 40 Hz in schizophrenic patients may reflect a dysfunction of the recurrent inhibitory drive on auditory neural net-works.