The stability of resting frontal electroencephalographic asymmetry in depression.

Although resting frontal electroencephalographic (EEG) alpha asymmetry has been shown to be a stable measure over time in nonclinical populations, its reliability and stability in clinically depressed individuals has not been fully investigated. The internal consistency and test-retest stability of resting EEG alpha (8-13 Hz) asymmetry were examined in 30 women diagnosed with major depression at 4-week intervals for 8 or 16 weeks. Asymmetry scores generally displayed good internal consistency and exhibited modest stability over the 8- and 16-week assessment intervals. Changes in asymmetry scores over this interval were not significantly related to changes in clinical state. These findings suggest that resting EEG alpha asymmetry can be reliably assessed in clinically depressed populations. Furthermore, intraclass correlation stability estimates suggest that although some traitlike aspects of alpha asymmetry exist in depressed individuals, there is also evidence of changes in asymmetry across assessment occasions that are not closely linked to changes in depressive severity.