EEG alpha power differences in the Icelandic winter between individuals with high vs. low risk for Seasonal Affective Disorder

Frontal alpha asymmetry in Major Depressive Disorder has been widely examined in EEG research. Recently, the EEG has also been suggested as a potential diagnostic biomarker for Seasonal Affective Disorder (SAD), a recurrent Major Depressive Disorder with a seasonal pattern. However, thus far no studies have been conducted in the dark Icelandic winter to examine whether frontal alpha asymmetry can be detected also among individuals with elevated risk for seasonality. EEG data was recorded in 122 participants (34 men) during rest (3 minutes) in spring, summer, fall and winter in Iceland. At each EEG assessment participants filled out the Seasonal Pattern Assessment Questionnaire (SPAQ). Based on the global seasonality score of the SPAQ, participants were divided into low and high seasonality groups. EEG power was analysed in the alpha frequency band over frontal, parietal, temporal, and occipital sites of the left and right hemisphere with an ANOVA. During fall/winter, EEG alpha power during resting state was higher in participants with elevated levels of seasonality (p = .004) as compared to participants with low levels of seasonality. The group difference interacted with region of interest (p < .001). Post-hoc tests revealed that the effect was particularly strong over the occipital lobe (p = .004). No significant effects were observed for resting state recordings in spring/summer. The findings suggest that EEG alpha power can be used as a diagnostic marker for seasonality and may further our understanding of SAD.