Frontal EEG alpha asymmetry, depression, and cognitive functioning

Davidson (1993) has proposed that hemispheric asymmetry in prefrontal activation, as measured by electroencephalographic (EEG) power in the alpha band (8-13Hz), is related to reactivity to affectively valenced stimuli. Davidson has proposed further that asymmetry is a stable trait, and that left frontal hypoactivation is a stable marker of vulnerability to depression. In Study 1, we tested Davidson's formulations by examining differences in frontal EEG alpha asymmetry among currently depressed, previously depressed, and never depressed subjects. As expected, currently and previously depressed subjects showed left frontal hypoactivation relative to never depressed controls, but did not differ significantly from each other. In Study 2, we explored the associations among frontal EEG asymmetry, response to a negative mood induction procedure, endorsement of dysfunctional cognitions, and attentional processing of valenced stimuli. Contrary to predictions, frontal EEG asymmetry was unrelated to mood reactivity and cognitive functioning. Theoretical and methodological implications of these findings are discussed.