The disorder in the spectrum of disinhibitory psychopathology in relation to which EEG activity is most often studied is ADHD. The most robust finding is of increased theta-band activity, as indicated above, along with reduced alpha or beta activity (Barry et al., 2003; Rommelse, Geurts, Franke, Buitelaar, & Hartman, 2011). These are sometimes combined into a theta/beta or theta/alpha ratio to serve as a neurobiological marker of the disorder (Snyder & Hall, 2006). Reduced beta power has also been found to correlate with behavior problems and hyperactivity in children (Deckel, Hesselbrock, & Bauer, 1996) and with a latent externalizing dimension, including substance abuse symptoms, in a community sample of adolescents (Gilmore, Malone, & Iacono, 2010). Thus, although the exact nature of EEG characteristics in disinhibitory psychopathology remains to be better delineated, especially the conditions governing the direction of change in beta activity (increased or decreased), these findings in aggregate suggest that beta EEG power has promise as an endophenotype for such disorders.
