The design of the present study was advantageous for examining the relationship between lifetime MDD and EEG asymmetry in women and men due to 1) the recruitment of a large sample of medically healthy, interview-diagnosed, medication-free individuals with no comorbid anxiety disorders; 2) repeated sessions of EEG recording that provided a reliable estimate of trait asymmetry; and, 3) a systematic examination of reference montages, including the first to examine the current-source density montage in depression. The consistency of the findings extended across both medial and lateral regions of frontal cortex, but different references indexed different aspects of depression, with the CSD-referenced data serving as a viable endophentype, whereas average- and linked mastoid-referenced data appear to show a female-specific relationship to depressive severity. The relationship to depressive severity was found across persons, not within persons over time, and there is no support from the literature that, within persons, changes in EEG asymmetry track changes in levels of symptoms over intervals of weeks or months (Allen, Urry, Hitt, & Coan, 2004; Debener et al., 2000). Future work can examine whether changes in severity over longer intervals tracks frontal asymmetry using average- and linked-mastoid references.
