Abstract
Symptoms of Major Depressive Disorder (MDD) are hypothesized to arise from dysfunction in brain networks linking the limbic system and cortical regions. Alterations in brain functional cortical connectivity in resting-state networks have been detected with functional imaging techniques, but neurophysiologic connectivity measures have not been systematically examined. We used weighted network analysis to examine resting state functional connectivity as measured by quantitative electroencephalographic (qEEG) coherence in 121 unmedicated subjects with MDD and 37 healthy controls. Subjects with MDD had significantly higher overall coherence as compared to controls in the delta (0.5–4 Hz), theta (4–8 Hz), alpha (8–12 Hz), and beta (12–20 Hz) frequency bands. The frontopolar region contained the greatest number of “hub nodes” (surface recording locations) with high connectivity. MDD subjects expressed higher theta and alpha coherence primarily in longer distance connections between frontopolar and temporal or parietooccipital regions, and higher beta coherence primarily in connections within and between electrodes overlying the dorsolateral prefrontal cortical (DLPFC) or temporal regions. Nearest centroid analysis indicated that MDD subjects were best characterized by six alpha band connections primarily involving the prefrontal region. The present findings indicate a loss of selectivity in resting functional connectivity in MDD. The overall greater coherence observed in depressed subjects establishes a new context for the interpretation of previous studies showing differences in frontal alpha power and synchrony between subjects with MDD and normal controls. These results can inform the development of qEEG state and trait biomarkers for MDD.
Highlights
Major Depressive Disorder (MDD) is characterized by dysphoric and anxious mood, difficulties in concentration and decision making, ruminative and self-referential thinking, as well as anhedonia and lack of motivation [1,2]
To further elucidate patterns of difference in functional connections between MDD and control subjects and characterize brain connectivity in the depressed state, we examined the mean length of the edges showing significant differences, as well as the locations of the nodes most commonly linked by significant edges
There was no significant association between mean edge or hub node value and severity of depression as measured by the 17-item Hamilton Depression Rating Scale, or between edge or hub node value and age. These results indicate that subjects with MDD differ significantly from healthy control subjects in patterns of brain functional connectivity
Summary
Major Depressive Disorder (MDD) is characterized by dysphoric and anxious mood, difficulties in concentration and decision making, ruminative and self-referential thinking, as well as anhedonia and lack of motivation [1,2] These symptoms are consistent with deficits seen in experimental paradigms, in which patients with MDD show deficits in emotional and cognitive information processing [3,4]. Cognitive deficits have been reported in memory processing, learning, attention, and executive function [7,8]. While clusters of these symptoms are used to define MDD, their neurobiological origins are not well understood [9]. Elucidating the linkage between the symptoms and pathophysiology of MDD could lead to more accurate and meaningful diagnoses that would have greater prognostic significance [10]
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