Intrinsic, task-evoked and absolute gamma synchrony during cognitive processing in first onset schizophrenia.

Cognitive deficits present from the first onset of schizophrenia are thought to arise from a core problem in neural synchrony. This is the first study to characterize the profile of gamma (30-100 Hz) synchrony (rather than power) and behavioral performance during higher-order cognitive processing in schizophrenia. Gamma synchrony was acquired from the EEG, and elicited by a Continuous Performance Test (CPT). We quantitated synchrony for regions associated with the fronto-parietal attention and visual networks for 59 young people with First Onset Schizophrenia (FOS) and 59 matched controls, facilitated by the BRAINnet.net data sharing initiative. We compared groups on gamma synchrony for intrinsic (pre-stimulus), task-evoked change (relative to baseline) and absolute (not relative to baseline) measures. Relationships between synchrony and CPT accuracy, symptoms and functioning were also assessed. FOS showed a reduced ability to modulate task-evoked changes in gamma synchrony, in the context of generally higher intrinsic and absolute synchrony, particularly in frontal regions. These gamma synchrony abnormalities in FOS were associated with performance on the CPT, but not with symptoms or functioning. Task-relevant changes in synchrony may be constrained by an overall excess of intrinsic background synchrony that is unrelated to specific task demands and this relates to cognitive performance. Results are in line with theoretical accounts of gamma synchrony as a core abnormality in schizophrenia, affecting functional connectivity in central executive circuits and causing cognitive symptoms. This study is the first to demonstrate that these gamma synchrony abnormalities are not limited to perceptual or lower-order cognitive processing.