Is resting state alpha asymmetry an indicator of depressive symptoms?

Introduction: Depression is a mood disorder characterized by persistent negative mood and anhedonia and is among the most burdensome conditions worldwide. Hence, identifying indicators of depression and its risk has been suggested to be a priority. One of the emerging potential indicators of depressive symptoms is resting state frontal alpha asymmetry (FAA) of electroencephalographic (EEG) activity, reflecting an unbalance between the approach and withdrawal motivational systems. FAA is defined as a relative difference in EEG alpha band power between the right and left frontal regions of the brain. Particularly, reduced alpha at the right compared to left frontal sites has been associated with withdrawal motivation and negative affect; while reduced alpha at left compared to right frontal sites has been related to approach motivation. Although FAA has been suggested to be a promising biomarker of depression, the literature on FAA in individuals with depressive symptoms has been inconclusive. Method: The present study aimed to investigate whether individuals with depressive symptoms are characterized by an unbalance between the approach and withdrawal motivational systems, indicated by resting state FAA. A group of young adults with subclinical depressive symptoms (or dysphoria, n =18, 18 F) and a group of healthy controls (n = 21, 20 F) underwent a 3-minute resting state EEG assessment. The asymmetry score was calculated for total alpha power by subtracting the natural log-transformed scores for each homologous left and right pair (i.e., ln[Right] - ln[Left]) in 3 scalp areas: frontal (F3 & F4), central (C3 & C4), and parietal (P3 & P4) areas. Repeated measures ANOVA with Group (without dysphoria, with dysphoria) as a between-subjects factor, and Area (frontal, central, parietal) as within-subjects factors, was performed on averaged asymmetry scores. Results and conclusion: Notable, no significant effect of FAA emerged in subjects with dysphoria compared to healthy controls, supporting the recent literature suggesting that FAA might not be a reliable marker of depressive symptoms.