Regional electroencephalographic asymmetries in bipolar seasonal affective disorder before and after exposure to bright light.

Electroencephalographic (EEG) asymmetries found in nonseasonal depression were examined in seasonal affective disorder before and after bright-light exposure. Subjects with seasonal depression demonstrated the expected pattern of frontal asymmetry both when depressed and following light-induced remission. Right-hemisphere EEG coherence, by contrast, served as a state-dependent indicator of seasonal depression.