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.

Keywords: cortical functional network; graph theory; ipolar disorder; resting-state EEG; schizophrenia.

Figure 1

(A) Brain regions showing significantly different nodal clustering coefficients (CCs) of the theta frequency band among patient groups and healthy controls. (B) Effect sizes of differences in nodal CCs of the theta frequency band among patient groups and healthy controls. Each bar indicates the effect size at each node. The upper bars indicate 74 regions in the left hemisphere and the lower bars indicate 74 regions in the right hemisphere. For reference, three dotted lines are drawn for small (0.01), medium (0.06), and large (0.14) effect sizes. The bars with numbers reveal significant differences among patient groups and the healthy controls (The p-value was adjusted via Bonferroni correction with 0.05/148 = 0.000338). The number “1” denotes brain regions where patient groups show significant differences from healthy controls. The number “2” denotes brain regions where patients with schizophrenia show significant differences from those with bipolar disorder. The number “3” denotes brain regions where patients with schizophrenia show significant differences from healthy controls.

Figure 2

Correlations between nodal clustering coefficients (CCs) and psychiatric, clinical, or cognitive measures in the theta band for each group. SOFAS, social and occupational functioning assessment scale; PANSS, positive and negative syndrome scale; KAVLT, Korean auditory verbal learning test.