Resting-State Gamma-Band Activity at Clinical High Risk for Schizophrenia: Correlation with Clinical Measures and Levels of GABA and Glutamate in Frontal Lobes

Gamma-band abnormalities are consistently reported in schizophrenia and attributed to disturbances of the excitation-inhibition balance in the brain. However, results in clinical high-risk groups are rare and quite inconsistent. The aim of the present study was to determine the characteristics of the restingstate gamma-band activity (range 30-45 Hz) in the clinical high-risk group (CHR, 110 patients) in comparison with schizophrenia patients (66 patients) and mentally healthy (62 subjects) male individuals. Correlation analysis with clinical characteristics were also conducted, and comparisons were made between patients who did or did not convert to psychosis during catamnestic follow-up. Correlations of gamma-band spectral power with gamma-aminobutyric acid (GABA) concentration and glutamine+glutamate index (GLX in frontal lobes were also analyzed. Statistically significant differences in gamma-band spectral power were revealed only between the CHR group and schizophrenia patients. In CHR patients GABA levels were decreased compared to healthy controls in the left frontal lobe, however there were no correlations between GABA and gamma-band spectral power. The results suggest some degree of “normality” or “compensation” of the processes of gamma-band activity generation (30-40 Hz) at clinical high risk of schizophrenia.