These findings implicate the possible role of CHRM2 in the generation and/or modulation of EROs. Theta and delta EROs depend on the level of acetylcholine. Muscarinic acetylcholine (M2) receptors inhibit presynaptic release of acetylcholine, leading to inhibition of irrelevant networks (cf. [181]). M2 are especially concentrated in the forebrain and possibly serve to maintain the effective balance of relevant/irrelevant networks, hence, having a direct influence on P3 generation [182]. Our results with the CHRM2 gene and brain oscillations support the role of acetylcholine in the generation of N2 (theta oscillations) and in the P3 component (delta and theta oscillations). A role of acetylcholine has been reported with regard to stimulus significance [183], selective attention [184], and P3 generation [185]. Administration of cholinergic agonists and antagonists have resulted in modified memory performance, as well as modified P3 amplitudes in humans [186-188]. In vitro administration of moderate amounts of the muscarinic agonist carbachol in the rat hippocampus induces synchronized delta oscillations, whereas higher concentrations produced short episodes of theta oscillations, and the carbachol-induced delta rhythms were not observed concurrent with carbachol-theta [189,190].
