Findings from CSD-referenced data indicated that a pattern of less relative left frontal activity (inferred from relatively greater left frontal alpha power) was evident for individuals with lifetime MDD compared to never-depressed individuals, regardless of sex or current severity of depressive symptoms. These findings clearly suggest the promise of CSD-referenced frontal EEG asymmetry as an endophenotype of depression risk. EEG asymmetry for average and linked mastoid references, however, showed evidence of sex-specific contributions related to current depressive symptom severity, reducing the likelihood that EEG asymmetry under these references montages can serve profitably as an endophenotypic marker of depression. For these references a pattern of less relative left frontal activity characterized women with currently high levels of depressive symptoms as compared to women with low levels of current depression. For men, by contrast, in the largest study of EEG asymmetry of depression to date, findings from the linked mastoid reference revealed that men with moderate or high levels of depressive symptoms showed relatively greater left frontal activity, a finding opposite to women, but nonetheless replicating one previous study with a sizable
