One of the most robust electrophysiological findings in alcoholism research is the reduced amplitude of the P3b event-related potential in alcoholics and individuals at high risk for alcoholism. The P3b ERP component occurs when an individual attends or responds to an infrequent but task-relevant target stimulus. It is defined as a centro-parietal positive voltage peak in the ERP waveform occurring between 300 to 500 milliseconds after target stimulus presentation. Reductions in P3b amplitudes (more prominent in visual compared with auditory paradigms) have consistently been reported in chronic alcoholics (Cohen et al., 2002; 1997; 1995; Emmerson et al., 1987; Glenn et al., 1996; Kamarajan et al., 2005; Pfefferbaum et al., 1991; 1987; Porjesz et al., 1987a; Prabhu et al., 2001; Suresh et al., 2003), and in individuals at high genetic risk for alcoholism. It has been proposed that P3b reduction is not a consequence of the effects of chronic excessive alcohol exposure but, rather, an endophenotypic marker reflecting the genetic predisposition toward alcoholism (Begleiter et al., 1984; Cohen et al., 1997; Hill and Steinhauer, 1993; O'Connor et al., 1986; Porjesz and Begleiter, 1990; Van der Stelt et al., 1998).
