A potentially important benefit of endophenotypes is that they can convey information about specific neurobiological and pathophysiological processes involved in the particular disorder with which they are associated (Iacono & Malone, 2011). EEG activity is intimately related to the organism’s level of arousal and attention, both of which are directly modulated by cholinergic pathways in the ascending reticular formation (Steriade, Gloor, Llinas, Lopes de Silva, & Mesulam, 1990). For instance, decreased discharge levels of cholinergic projections to basal forebrain neurons results in large EEG slow waves, such as those observed during sleep. Noradrenergic modulation complements cholinergic activity during waking states (Steriade et al., 1990). In general, the specific form of EEG activity, particularly the magnitude of activity and the frequency of EEG oscillations, reflects the balance between excitatory and inhibitory neuronal interactions, both within and between populations of neurons (David & Friston, 2003). Different frequencies of oscillations in turn are consistently associated with particular cognitive and perceptual states. The alpha rhythm, for example, originates in multiple thalamocortical projections (Lopes da Silva, Vos, Mooibroek, & Van Rotterdam, 1980), and it is
