Recent research suggests that ERPs are not unitary phenomena but are formed through the superposition of multiple event-related oscillations (EROs) (Gruber and others 2005; Makeig and others 2002). The P3 response is primarily composed of superimposed delta (1–3 Hz) and theta (4–7 Hz) frequency band energy with delta energy more concentrated in the posterior region and theta more fronto-central (Basar-Eroglu and others 1992) (Basar and others 1999; Karakas and others 2000; Schutte and others 1999). Using ERO data underlying the target visual evoked P3 component, we (Jones and others 2004) have found significant linkage and linkage disequilibrium on chromosome 7 with theta band (4–7 Hz) EROs. The gene encoding the muscarinic acetylcholine receptor M2 (CHRM2) is located under the observed linkage peak. Linkage disequilibrium (LD) analysis revealed significant association between CHRM2 single nucleotide polymorphisms (SNPs) and both delta (1–3 Hz) and theta (4–7 Hz) band ERO data (Jones and others 2004). Recent evidence from COGA indicates that the CHRM2 gene is not only associated with EROs underlying P3 but also clinical diagnosis, i.e., alcohol dependence and depression (Wang and others 2004).
