Hypofunction of directed brain network within alpha frequency band in depressive patients: a graph-theoretic analysis.

Directed brain networks may provide new insights into exploring physiological mechanism and neuromarkers for depression. This study aims to investigate the abnormalities of directed brain networks in depressive patients. We constructed the directed brain network based on resting electroencephalogram for 19 depressive patients and 20 healthy controls with eyes closed and eyes open. The weighted directed brain connectivity was measured by partial directed coherence for α, β, γ frequency band. Furthermore, topological parameters (clustering coefficient, characteristic path length, and et al.) were computed based on graph theory. The correlation between network metrics and clinical symptom was also examined. Depressive patients had a significantly weaker value of partial directed coherence at alpha frequency band in eyes-closed state. Clustering coefficient and characteristic path length were significantly lower in depressive patients (both  < .01). More importantly, in depressive patients, disruption of directed connectivity was noted in left-to-left ( < .05), right-to-left ( < .01) hemispheres and frontal-to-central ( < .01), parietal-to-central ( < .05), occipital-to-central ( < .05) regions. Furthermore, connectivity in LL and RL hemispheres was negatively correlated with depression scale scores (both  < .05). Depressive patients showed a more randomized network structure, disturbed directed interaction of left-to-left, right-to-left hemispheric information and between different cerebral regions. Specifically, left-to-left, right-to-left hemispheric connectivity was negatively correlated with the severity of depression. Our analysis may serve as a potential neuromarker of depression.