The effects of gender and depression severity on the association between alpha asymmetry and depression across four brain regions.

Data describing the association between EEG asymmetry and depression status have been equivocal. Effects from brain regions involved, depression severity, and the generalisability of findings across genders, have been inconsistently examined and/or verified. This study investigated these issues within a community sample to potentially expand the asymmetry hypothesis to non-severe depression participants. The singular effects of brain region and electrode site, gender, and depression severity, plus the interaction between gender and depression severity across brain regions were investigated in a study of alpha asymmetry among 46 males and 54 females (M age=32.5 yr, SD=14.13 yr) using the Self-rating Depression Scale (Zung, 1973). There was no significant difference across genders or age for depression severity. Dichotomous classification of depressed state produced similar but slightly different results from analysis of the whole range of depression status, although the frontal region was the only area where depression was consistently significantly associated with EEG asymmetry, and then only for females. However, the direction of those differences for females was opposite of that predicted by the EEG asymmetry-depression hypothesis. Several methodological issues that may have contributed to these findings are discussed, with suggestions made for future research that focusses upon individual depression symptom profiles rather than dichotomous or total depression scores in order to assist in developing a clinically-relevant model of EEG asymmetry in depressed persons.