Depressed individuals appear to be characterized by a pattern of relatively less left than right resting frontal activity (inferred by relatively greater left than right alpha band activity; see Allen, Coan, & Nazarian, 2004), which is thought to reflect reduced approach motivation and decreased responsiveness to reward. Moreover, this pattern distinguishes both symptomatic and remitted depressed individuals from never-depressed individuals, suggesting that frontal EEG asymmetry may be a trait-like liability marker for development of depression (e.g., Allen, Urry, Hitt, & Coan, 2004b; Coan & Allen, 2003, Gotlib, Ranganath, & Rosenfeld, 1998; Henriques & Davidson, 1990, 1991). Consistent with this hypothesis, research has also demonstrated relatively less left frontal activity in children of depressed mothers (e.g., Dawson, Fray, Panagiotides, Osterling, & Hessl, 1997). Studies examining the heritability of frontal EEG asymmetry have determined that this pattern of frontal regional brain activity has a significant genetic component (Anokhin, Heath, & Myers, 2006; Smit, Posthuma, Boomsma, & DeGeus, 2007) but EEG asymmetry may only relate to anxiety and depression risk in young women, not men (Smit et al., 2007), suggesting that further research is needed to explore sex differences in this potential endophenotype for depression.
