Validity and reliability of electroencephalographic frontal alpha asymmetry and frontal midline theta as biomarkers for depression.

Electroencephalographic (EEG) frontal alpha asymmetry (FAA) and frontal midline (FM) theta have been suggested as biomarkers for depression and anxiety, but have mostly been assessed in small and non-clinical studies. In a clinical sample of 79 adults with depression (ICD-10: F32), resting EEG and scales of depression (MADRS) and anxiety (HADS-A) were measured at intake and after 3 months. FAA and FM theta values were referenced to a normative population database. Internal consistency, test-retest reliability, and correlations with psychiatric tests were examined. Reliability was sufficient. However, FAA and FM theta values were close to the general population, and correlations with psychiatric tests were mostly small and non-significant, with the exception of FAA on F7-F8 z-scores and HADS-A. We conclude that the validity of FAA and FM theta and therefore their potential as biomarkers for depression and anxiety remain unclear.