Disturbances in theta-beta band oscillations in precuneus and aberrant effective connectivity within default mode network as potential biomarkers of chronic schizophrenia: an EEG resting-state study

Abstract

Schizophrenia is a complex psychiatric disorder with unknown neuropathology. Notably, the triple-network-model of psychiatric disorders, focusing on the default mode (DMN), central executive (CEN), and salience (SN) networks, proposes an interesting framework for investigating abnormal neurocircuit activity in schizophrenia. In the present study, we aim to explore the three resting-state EEG biomarkers: i) the relative power spectrum, ii) functional connectivity metrics - corrected imaginary phase locking (ciPLV) and iii) effective connectivity estimated by source-localization-based directed transfer function (DTF) in 28 chronic schizophrenia patients and 27 controls. The presented results revealed that schizophrenia is characterised by: i) the prevalence of high power at the theta band (4–8 Hz) localised at the centroparietal area, along with smaller but widespread alterations in frontotemporal regions; ii) the existence of widespread bilateral alterations in inter- and intra-hemispheric neural communication patterns, with the most significant difference, manifested in a reversed pattern of hemispheric engagement at theta and beta/gamma bands; iii) the observed multiband effective connectivity disturbances within the DMN were revealed as the most excessive, compared to the solely low-frequency alterations of CEN or SN negative ones; the most significant difference between group was manifested in a reversed direction of information flows at theta and beta bands, with a strong indication of the specific disturbances of key DMN node – the precuneus. In conclusion, our study presents novel insights into schizophrenia neuropathology, with a particular emphasis on the fronto-parietal connectivity alterations at theta/beta bands. This may be suggested as a promising clinical biomarker of chronic schizophrenia.