On 2015 Oct 21, Gerard Bruder commented:

Jesulola et al. (2015) reviewed the literature of EEG alpha asymmetry in relation to behavioral withdrawal in depression. One of the confusing issues in this literature is whether one is referring to hemispheric asymmetry of EEG alpha (α) or brain activity, which is thought to be inversely related to alpha. To their credit, the authors attempted to deal with this by using separate abbreviations for the direction of alpha asymmetry in depression (Lα > Rα) and asymmetry of brain activity (Ra > La). The problem is that these were not consistently used in describing findings in literature. Specifically, on page 60 (3.2.1.4) in referring to the findings of Lopez-Duran et al. (2012), they state that “greater relative left frontal activation (i.e., the opposite of the La>Ra finding for depressed individuals)” but the typical finding for depression is greater right than left frontal activity (Ra>La). Immediately below, in referring to the findings of Bruder et al. (2007), they state “that children whose parents and grandparents were depressed demonstrated greater Lα > Rα EEG asymmetry in the parietal…”, but it should be La>Ra, meaning that activity was less over right than left parietal sites. In section 3.2.2.1 on this page, they state “other studies have examined EEG asymmetry in participants with comorbid anxiety and depression”…and “In general, depressed patients who also had an anxiety disorder had the opposite direction EEG asymmetry (i.e., La>Ra) than depressed patients who did not have comorbid anxiety, although most significant findings have been reported in the parietal sites.” The Bruder et al. (1997) study referred to, which measured EEG alpha in depressed patients with versus without a comorbid anxiety disorder, found greater activity over right than left parietal sites in those with a comorbid anxiety disorder and so it should read “Ra>La”. The other EEG studies referred to were in non-clinical samples or did not include resting alpha measures. They also state, “This contrary finding is unpredicted as it might be expected that co-morbid anxiety and depression might combine to give a much larger Ra>La frontal asymmetry...” The Bruder et al. (1997) study actually found the co-morbid group had Ra>La at frontal sites, whereas depressed patients without an anxiety disorder did not, and so the having both an anxiety and depressive disorder was associated with Ra>La. It was only at parietal sites where the alpha asymmetry in the co-morbid group (Ra>La) was opposite to depressed patients without an anxiety disorder (La>Ra). The favoring of right over left parietal activity in the co-morbid patients could reflect hyperactivation of right parietal regions due to anxious arousal (Heller et al., 1997), hypoactiation of left hemisphere regions or some combination of both (Bruder et al. 1999).

The authors also discuss several key research issues that require addressing for this field to move forward. The issue of where EEG asymmetry occurs in depression is important and can be dealt with by including frontal and more posterior electrode sites. However, this review does not mention more recent methodological developments, in particular application of current source density (CSD), that can refine the quantification and spatial resolution of EEG measures, improving neuroanatomical and spectral resolution (Tenke et al., 2005; Tenke & Kayser, 2015; Tenke et al., 2015; Kayser & Tenke, 2015). The use of CSD measures also deals with the EEG “reference” problem, which no doubt contributed to differences in alpha asymmetry findings across studies, and can lead to greater consistency of EEG findings between studies using “resting” and task-based EEG measures (Stewart et al., 2014). References Bruder, G.E., Fong, R., Tenke, C.E., Leite, P., Towey, J.P., Stewart, J.E., McGrath, P.J., Quitkin, F.M (1997). Regional brain asymmetries in major depression with or without an anxiety disorder: a quantitative electroencephalographic study. Biological Psychiatry, 41(9), 939-948. Bruder, G.E., Tenke, C.E., Warner, V., Weissman, M.M. (2007). Grandchildren at high and low risk for depression differ in EEG measures of regional brain asymmetry. Biological Psychiatry, 62(11), 1317-1323. Bruder, G.E., Wexler, B.E., Stewart, J.W., Price, L.H. (1999). Perceptual asymmetry differences between major depression with or without a comorbid anxiety disorder: A dichotic listening study. Journal of Abnormal Psychology, 108 (2), 233-239. Heller, W., Nitschke, J.B., Etienne, M.A., Miller, B.A. (1997). Patterns of regional brain activity differentiate types of anxiety. Journal of abnormal Psychology, 106, 376-385. Kayser, J., Tenke, C.E. (2015). Issues and considerations for using the scalp surface Laplacian in EEG/ERP research: A tutorial review. International Journal of Psychophysiology, 97(3), 189-209. Lopez-Duran, N.I., Nusslock, R., George, C., Kovacs, M. (2012). Frontal EEG asymmetry moderates the effects of stressful life events on internalizing symptoms in children at familial risk for depression. Psychophysiology, 49 (4), 510-521. Tenke, C.E., Kayser, J. (2015). Surface Laplacians (SL) and phase properties of EEG rhythms: simulated generators in a volume-conduction model. International Journal of Psychophysiology, 97(3), 285-298. Tenke, C.E., Kayser, J., Abraham, K., Alvarenga, J.E., Bruder, G.E. (2015). Posterior EEG alpha at rest and during task performance: comparison of current source density and field potential measures. International Journal of Psychophysiology, 97(3), 299-309. Stewart, J.L., Coan, J.A., Towers, D.N., Allen, J.J.B. (2014). Resting and task-related prefrontal EEG asymmetry in depression: Support for the capability model. Psychophysiology 51, 446-455.

On 2015 Oct 21, Gerard Bruder commented:

Jesulola et al. (2015) reviewed the literature of EEG alpha asymmetry in relation to behavioral withdrawal in depression. One of the confusing issues in this literature is whether one is referring to hemispheric asymmetry of EEG alpha (α) or brain activity, which is thought to be inversely related to alpha. To their credit, the authors attempted to deal with this by using separate abbreviations for the direction of alpha asymmetry in depression (Lα > Rα) and asymmetry of brain activity (Ra > La). The problem is that these were not consistently used in describing findings in literature. Specifically, on page 60 (3.2.1.4) in referring to the findings of Lopez-Duran et al. (2012), they state that “greater relative left frontal activation (i.e., the opposite of the La>Ra finding for depressed individuals)” but the typical finding for depression is greater right than left frontal activity (Ra>La). Immediately below, in referring to the findings of Bruder et al. (2007), they state “that children whose parents and grandparents were depressed demonstrated greater Lα > Rα EEG asymmetry in the parietal…”, but it should be La>Ra, meaning that activity was less over right than left parietal sites. In section 3.2.2.1 on this page, they state “other studies have examined EEG asymmetry in participants with comorbid anxiety and depression”…and “In general, depressed patients who also had an anxiety disorder had the opposite direction EEG asymmetry (i.e., La>Ra) than depressed patients who did not have comorbid anxiety, although most significant findings have been reported in the parietal sites.” The Bruder et al. (1997) study referred to, which measured EEG alpha in depressed patients with versus without a comorbid anxiety disorder, found greater activity over right than left parietal sites in those with a comorbid anxiety disorder and so it should read “Ra>La”. The other EEG studies referred to were in non-clinical samples or did not include resting alpha measures. They also state, “This contrary finding is unpredicted as it might be expected that co-morbid anxiety and depression might combine to give a much larger Ra>La frontal asymmetry...” The Bruder et al. (1997) study actually found the co-morbid group had Ra>La at frontal sites, whereas depressed patients without an anxiety disorder did not, and so the having both an anxiety and depressive disorder was associated with Ra>La. It was only at parietal sites where the alpha asymmetry in the co-morbid group (Ra>La) was opposite to depressed patients without an anxiety disorder (La>Ra). The favoring of right over left parietal activity in the co-morbid patients could reflect hyperactivation of right parietal regions due to anxious arousal (Heller et al., 1997), hypoactiation of left hemisphere regions or some combination of both (Bruder et al. 1999).

The authors also discuss several key research issues that require addressing for this field to move forward. The issue of where EEG asymmetry occurs in depression is important and can be dealt with by including frontal and more posterior electrode sites. However, this review does not mention more recent methodological developments, in particular application of current source density (CSD), that can refine the quantification and spatial resolution of EEG measures, improving neuroanatomical and spectral resolution (Tenke et al., 2005; Tenke & Kayser, 2015; Tenke et al., 2015; Kayser & Tenke, 2015). The use of CSD measures also deals with the EEG “reference” problem, which no doubt contributed to differences in alpha asymmetry findings across studies, and can lead to greater consistency of EEG findings between studies using “resting” and task-based EEG measures (Stewart et al., 2014). References Bruder, G.E., Fong, R., Tenke, C.E., Leite, P., Towey, J.P., Stewart, J.E., McGrath, P.J., Quitkin, F.M (1997). Regional brain asymmetries in major depression with or without an anxiety disorder: a quantitative electroencephalographic study. Biological Psychiatry, 41(9), 939-948. Bruder, G.E., Tenke, C.E., Warner, V., Weissman, M.M. (2007). Grandchildren at high and low risk for depression differ in EEG measures of regional brain asymmetry. Biological Psychiatry, 62(11), 1317-1323. Bruder, G.E., Wexler, B.E., Stewart, J.W., Price, L.H. (1999). Perceptual asymmetry differences between major depression with or without a comorbid anxiety disorder: A dichotic listening study. Journal of Abnormal Psychology, 108 (2), 233-239. Heller, W., Nitschke, J.B., Etienne, M.A., Miller, B.A. (1997). Patterns of regional brain activity differentiate types of anxiety. Journal of abnormal Psychology, 106, 376-385. Kayser, J., Tenke, C.E. (2015). Issues and considerations for using the scalp surface Laplacian in EEG/ERP research: A tutorial review. International Journal of Psychophysiology, 97(3), 189-209. Lopez-Duran, N.I., Nusslock, R., George, C., Kovacs, M. (2012). Frontal EEG asymmetry moderates the effects of stressful life events on internalizing symptoms in children at familial risk for depression. Psychophysiology, 49 (4), 510-521. Tenke, C.E., Kayser, J. (2015). Surface Laplacians (SL) and phase properties of EEG rhythms: simulated generators in a volume-conduction model. International Journal of Psychophysiology, 97(3), 285-298. Tenke, C.E., Kayser, J., Abraham, K., Alvarenga, J.E., Bruder, G.E. (2015). Posterior EEG alpha at rest and during task performance: comparison of current source density and field potential measures. International Journal of Psychophysiology, 97(3), 299-309. Stewart, J.L., Coan, J.A., Towers, D.N., Allen, J.J.B. (2014). Resting and task-related prefrontal EEG asymmetry in depression: Support for the capability model. Psychophysiology 51, 446-455.