Frontal asymmetry as a mediator and moderator of emotion: An updated review.

For over 35 years, research has examined frontal alpha EEG asymmetry, discussed in terms of relative left frontal activity (rLFA) in the present review, as a concurrent and prospective marker of affective processing and psychopathology. Because rLFA may index (a) neural correlates of frontal asymmetry, or (b) psychological constructs to which frontal asymmetry relates, rLFA can advance our understanding of both neural and psychological models of emotion and psychopathology. In order to improve such understanding, the specific role of rLFA in extending or challenging existing theory must be clear to researchers and readers alike. In particular, in 2004, Coan and Allen argued that examination of rLFA as a mediator or moderator may improve our theoretical understanding of rLFA. Despite being a commonly cited paper in the field, most rLFA research today still fails to acknowledge the statistical role of rLFA in the research. The aim of the present paper is to (a) convince the reader of the importance of distinguishing rLFA as a predictor, outcome, mediator, or moderator in order to conduct theory-driven research, and (b) highlight some of the major advances in rLFA literature since the review by Coan and Allen (2004) in the framework of mediators and moderators. We selected a broad range of search terms to capture relevant rLFA research and included only those studies utilizing established methods for rLFA measurement.