Asymmetrical frontal cortical activity associated with differential risk for mood and anxiety disorder symptoms: An RDoC perspective

The recently launched NIMH Research Domain Criteria (RDoC) initiative aims to examine the relationship between core biobehavioral dimensions and symptom profiles that either cut across traditional disorder categories or that are unique to specific clinical phenomenon. A biobehavioral construct that has received considerable attention and that is directly relevant to the Positive Valence Systems domain of the RDoC initiative is approach motivation. One way approach motivation is frequently operationalized is left versus right frontal electroencephalographic (EEG) activity, with greater relative left frontal EEG activity reflecting increased approach motivation and decreased relative left frontal EEG activity reflecting decreased approach motivation or increased withdrawal tendencies. The objective of the present review paper is to examine the relationship between relative left frontal EEG activity and mood and anxiety related symptoms from an RDoC perspective. We first provide an overview of the approach–withdrawal motivational model of frontal EEG asymmetry. Second, we review evidence that relative left frontal EEG activity is associated with a differential risk for unipolar depression versus bipolar disorder. Third, and in line with the mission statement of the RDoC, we move beyond considering mood and anxiety disorders as unitary constructs or homogenous disorders and instead propose that individual differences in relative left frontal EEG activity may be uniquely associated with specific symptom clusters of depression (i.e., anhedonia), hypomania/mania (i.e., symptoms characterized by excessive approach motivation), and anxiety (i.e., anxious apprehension versus anxious arousal). Identifying the relationship between relative left frontal EEG activity and specific mood and anxiety-related symptom clusters has important implications for clinical science, assessment, and treatment.