Auditory Cortex Volume and Gamma Oscillation Abnormalities in Schizophrenia

We investigated whether the gray matter volume of primary auditory cortex (Heschl's gyrus [HG]) was associated with abnormal patterns of auditory γ activity in schizophrenia, namely impaired γ synchronization in the 40-Hz auditory steady-state response (ASSR) and increased spontaneous broadband γ power. (The γ data were previously reported in Hirano et al, JAMA Psychiatry, 2015;72:813-821). Participants were 24 healthy controls (HC) and 23 individuals with chronic schizophrenia (SZ). The ASSR was obtained from the electroencephalogram to click train stimulation at 20, 30, and 40 Hz rates. Dipole source localization of the ASSR was used to provide a spatial filter of auditory cortex activity, from which ASSR evoked power and phase locking factor (PLF), and induced γ power were computed. HG gray matter volume was derived from structural magnetic resonance imaging at 3 T with manually traced regions of interest. As expected, HG gray matter volume was reduced in SZ compared with HC. In SZ, left hemisphere ASSR PLF and induced γ power during the 40-Hz stimulation condition were positively and negatively correlated with left HG gray matter volume, respectively. These results provide evidence that cortical gray matter structure, possibly resulting from reduced synaptic connectivity at the microcircuit level, is related to impaired γ synchronization and increased spontaneous γ activity in schizophrenia.