The electroencephalogram (EEG) records brain electrical activity using non-invasive scalp electrodes when the subject is either at rest, producing ongoing state measurements of neuroelectrical activity, or engaged in cognitive tasks, yielding event-related potentials (ERPs) that are time-locked to specific stimuli, events or processes. The P300 signal is perhaps the best studied ERP [Porjesz et al, 2005]; it is a large positive component occurring between 300-600 ms after a stimulus (Figure 1). This neuroelectrical component is highly heritable [O’Connor et al., 1994; Katsanis et al., 1997; Almasy et al., 1999], associated with brain structure integrity [McCarley et al., 1993; Ford et al., 1994] and with various task-related cognitive processes [Verleger, 1988; Tomberg and Desmedt, 1998; Polich and Herbst, 2000]. The neurochemical underpinnings of P300 are unclear, although available data suggest the involvement of strong GABAergic, cholinergic and glutamatergic interactions that elicit excitatory and inhibitory post-synaptic potentials, with indirect dopaminergic, nor-adrenergic and serotonergic modulating effects [Frodl-Bauch et al., 1999; Polich, 2007]. Various neurological disorders display reductions in P300 amplitude and prolonged latency, foremost being alcohol dependence [Porjesz and Begleiter, 1998] and schizophrenia [Ford et al., 1999], as well as a spectrum of externalizing disorders [Iacono et al., 2003].
