Temporal stability of posterior EEG alpha over twelve years.

OBJECTIVE: We previously identified posterior EEG alpha as a potential biomarker for antidepressant treatment response. To meet the definition of a trait biomarker or endophenotype, it should be independent of the course of depression. Accordingly, this report evaluated the temporal stability of posterior EEG alpha at rest.

METHODS: Resting EEG was recorded from 70 participants (29 male; 46 adults), during testing sessions separated by 12 ± 1.1 years. EEG alpha was identified, separated and quantified using reference-free methods that combine current source density (CSD) with principal components analysis (PCA). Measures of overall (eyes closed-plus-open) and net (eyes closed-minus-open) posterior alpha amplitude and asymmetry were compared across testing sessions.

RESULTS: Overall alpha was stable for the full sample (Spearman-Brown [rSB ] = .834, Pearson's r = .718), and showed excellent reliability for adults (rSB  = .918; r = 0.848). Net alpha showed acceptable reliability for adults (rSB  = .750; r = .600). Hemispheric asymmetries (right-minus-left hemisphere) of posterior overall alpha showed significant correlations, but revealed acceptable reliability only for adults (rSB  = .728; r = .573). Findings were highly comparable between 29 male and 41 female participants.

CONCLUSIONS: Overall posterior EEG alpha amplitude is reliable over long time intervals in adults.

SIGNIFICANCE: The temporal stability of posterior EEG alpha oscillations at rest over long time intervals is indicative of an individual trait.