Event-related potentials (ERPs) provide a non-invasive tool to explore the characteristics of sensory processes and higher cognitive function in the brain. The P3 (or P300) component is possibly the best-studied ERP. This positive electric potential deflection is elicited approximately 300–500 ms following the occurrence of infrequent stimuli during an oddball experimental paradigm. P3 is highly heritable (Almasy and others 1999; Katsanis and others 1997; O'Connor and others 1994) and it provides quantitative endophenotypes for some complex psychiatric disorders, including disinhibitory disorders such as alcohol or substance-related disorders, conduct disorder, attention-deficit hyperactive disorder (ADHD), antisocial personality disorder (ASP), impulse control disorders (Hesselbrock and others 2001; Porjesz and others 2005). Therefore, identifying specific genetic variants that modulate the P3 and other related electrophysiological measures is a rational strategy to search for genes associated with the relevant psychiatric disorders. By using this strategy, genetic analysis of P300 amplitude data from the Collaborative Study on the Genetics of Alcoholism (COGA) has revealed significant linkage on a number of chromosomes with alcohol dependence and other disinhibitory disorders (e.g., Begleiter and others 1998; Porjesz and others 2004).
