Gamma Frequency–Range Abnormalities to Auditory Stimulation in Schizophrenia

TLDR

Gamma‑range (30–50 Hz) neural synchronization, dependent on glutamatergic excitation–inhibition interplay, is a key information‑processing mechanism that may be disrupted in schizophrenia. The study examined whether auditory neural networks in schizophrenia can support gamma‑range synchronization. EEG was recorded from 15 patients and 15 matched controls while they received 20–40 Hz click trains, and the power and phase relationships at each frequency, especially 40 Hz, were compared between groups. Schizophrenia patients showed reduced 40 Hz EEG power, delayed phase‑synchronization onset and desynchronization, indicating selective deficits in early‑stage sensory processing likely due to impaired recurrent inhibitory drive.

Abstract

<h3>Background</h3> Basic science studies at the neuronal systems level have indicated that gamma-range (30-50 Hz) neural synchronization may be a key mechanism 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 excitatory projection neurons and inhibitory neurons utilizing γ-aminobutyric acid (GABA), which postmortem studies suggest may be abnormal in schizophrenia. We therefore tested whether auditory neural networks in patients with schizophrenia could support gamma-range synchronization. <h3>Methods</h3> Synchronization of the electroencephalogram (EEG) to different rates (20-40 Hz) of auditory stimulation was recorded from 15 patients with schizophrenia and 15 sex-, age-, and handedness-matched control subjects. The EEG power at each stimulation frequency was compared between groups. The time course of the phase relationship between each stimulus and EEG peak was also evaluated for gamma-range (40 Hz) stimulation. <h3>Results</h3> Schizophrenic patients showed reduced EEG power at 40 Hz, but not at lower frequencies of stimulation. In addition, schizophrenic patients showed delayed onset of phase synchronization and delayed desynchronization to the click train. <h3>Conclusions</h3> These data provide new information on selective deficits in early-stage sensory processing in schizophrenia, a failure to support the entrainment 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 networks.