Altered Cortical Functional Networks in Patients With Schizophrenia and Bipolar Disorder: A Resting-State Electroencephalographic Study

Abstract

Background: Pathologies of schizophrenia and bipolar disorder have been poorly understood. Brain network analysis could help understand brain mechanisms of schizophrenia and bipolar disorder. This study investigates the source-level brain cortical networks using resting-state electroencephalography (EEG) in patients with schizophrenia and bipolar disorder. Methods: Resting-state EEG was measured in 38 patients with schizophrenia, 34 patients with bipolar disorder type I, and 30 healthy controls. Graph theory based source-level weighted functional networks were evaluated: strength, clustering coefficient (CC), path length (PL), and efficiency in six frequency bands. Results: At the global level, patients with schizophrenia or bipolar disorder showed higher strength, CC, and efficiency, and lower PL in the theta band, compared to healthy controls. At the nodal level, patients with schizophrenia or bipolar disorder showed higher CCs, mostly in the frontal lobe for the theta band. Particularly, patients with schizophrenia showed higher nodal CCs in the left inferior frontal cortex and the left ascending ramus of the lateral sulcus compared to patients with bipolar disorder. In addition, the nodal-level theta band CC of the superior frontal gyrus and sulcus (cognition-related region) correlated with positive symptoms and social and occupational functioning scale (SOFAS) scores in the schizophrenia group, while that of the middle frontal gyrus (emotion-related region) correlated with SOFAS scores in the bipolar disorder group. Conclusions: Altered cortical networks were revealed and these alterations were significantly correlated with core pathological symptoms of schizophrenia and bipolar disorder. These source-level cortical network indices could be promising biomarkers to evaluate patients with schizophrenia and bipolar disorder.

Alteration of Cortical Functional Networks in Default-Mode Network-Related Regions in Mood Disorders with Resting-State Electroencephalography

“…Kim et al 34 showed decreased CC and e ciency, and increased PL in the alpha band during resting-state EEG in patients with BD. Another resting-state EEG study demonstrated that BD showed higher strength and CC, and lower PL in the theta band 35 . Furthermore, several neuroimaging studies have shown altered functional brain networks in MDD patients.…”

“…Effect sizes were computed based on the partial eta squared (η 2 ). The procedure for the statistical analysis followed our previous study 35 .…”

“…For instance, Kim et al 34 observed decreased CC and e ciency, and increased PL in the alpha band in patients with BD. In addition, BD showed higher strength and CC and lower PL in the theta band 35 . In terms of MDD, lower PL and CC and greater e ciency have been reported 36,37 .…”

“…EEG signals were bandpass ltered from 0.1 to 100 Hz with a 1,000-Hz sampling rate. The procedure for the EEG recording followed our previous study 35 .…”

“…Then, the time series of the cortical sources at each of the 68 seed points were bandpass ltered and divided into six frequency bands: delta (1-4 Hz), theta (4-8 Hz), alpha (8)(9)(10)(11)(12), low beta (12)(13)(14)(15)(16)(17)(18), high beta (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30), and gamma . The procedure for the source localization followed that of our previous study 35 . 4…”