The present study indicates that a pattern of relatively less left frontal EEG activity as measured by the current source density reference reflects a trait-like marker of depression risk for men and women, whereas a similar pattern of EEG asymmetry measured by average and linked mastoid references appears to reflect a severity-related marker of current depression, at least in women. Since the current source density algorithm attenuates broad electrical sources, such as distal parietal and occipital sources where EEG alpha activity is typically quite large (Hagemann et al., 2001; Kayser & Tenke, 2006), it is more probable that the trait-like index of current source density-referenced EEG asymmetry reflects predominantly frontal sources. By contrast, the severity-related indices of EEG asymmetry derived from AVG, LM, and Cz reference montages will potentially reflect considerable nonfrontal activity, since these references reflect both proximal and distal sources, in part due to lower signal-to-noise ratios in the measurement of frontal EEG activity than those derived from the CSD reference (Hagemann et al., 2001). In order for frontal EEG asymmetry to be an endophenotype for depression risk
