Högskolan i Skövde

A relative less right than left resting frontal alpha activity has been associated with depression, but the research of frontal alpha asymmetry (FAA) has over the years shown inconsistent results. In this present meta-analysis, a mixed approach of the two previous meta-analyses (Thibodeau, Jorgensen, & Kim, 2006; van der Vinne, Vollebregt, van Putten, & Arns, 2017) was adopted. The aim was to cover the FAA research comprising three frontal pair sites FP1-FP2, F3-F4, F7-F8, and both central and non-central reference schemes. The sample consisted of 10 studies with a total of subjects: major depressive disorder (MDD) n = 320 and healthy controls n = 235. The overall result of the statistical analysis including all studies independent of reference or pair site showed no significant differences in FAA between MDD and controls. However, sub-analyses did reveal a significant difference at pair site FP1-FP2 when central references were used (medium effect size, standardized mean difference (SMD) = -0.56), and at F3-F4 when non-central references were used (small to medium effect size, SMD = -0.41). The direction of the asymmetry was further assessed and did not seem to give much support to a depressed brain to be associated with relatively less frontal alpha activity in the right as compared to the left hemisphere. Additionally, the results of this meta-analysis did seem to indicate that the choice of reference and pair site might have an effect on the results of FAA.