Introduction: Neuronal assemblies are able to create discreet and meaningful representations of objects from complex scenes in any sensory modality. Such processing of complex input requires flexible, reliable and ubiquitous mechanisms to link multiple regions of the brain in a timeframe of milliseconds. A proposed linking or binding mechanism is synchronous neural activity in the gamma frequency wave band. A disruption to this mechanism has been proposed as a possible result of the pathology underlying psychotic illnesses. This study examines the distribution of abnormal gamma synchrony in first episode psychosis. Methods: 36 subjects with first episode psychosis from age 14 to 24 years underwent a standard auditory oddball paradigm during electroencephalogram analysis. The data were analysed to produce a topographical distribution of abnormal synchrony to background and target stimuli. Symptom profile was assessed using PANSS. Ninety-eight age, sex and education matched controls underwent the same procedure. Gamma synchrony measures were calculated for each background and target stimulus with a 128-sample Welch window moved along sample by sample, 500 ms prior to each stimulus (-500 ms) to 750 ms after the stimulus. At each sample position, the phase of the Gamma frequency component was computed by means of FFT, yielding a time series of Gamma phase from -500 to 750 ms for each single-trial from each site. Abnormal gamma findings within the psychosis group were determined with MANOVA, and the duration of treatment, drug dose and years of education were corrected for with MANCOVA. Results: Abnormal and persistently elevated gamma synchrony was detected in the left temporal regions of subjects with first episode psychosis. The findings complement previous findings from functional and structural imaging studies indicating the left temporal region as a key site of pathology in early psychosis. The results are also consistent with the speculative hypothesis that an excess of synchronous gamma activity reflecting a tendency to erroneous neural assembly formation and subsequent delusional or hallucinatory experiences.
- Biological psychiatry