Generation of theta and delta oscillations depends on level of activation of M2 muscarinic autoreceptors (Fellous and Sejnowski, 2000; Tiesinga et al., 2001) that inhibit further acetylcholine release by presynaptic cells, leading to inhibition of irrelevant networks. Acetylcholine plays a significant role in stimulus significance (Perry et al., 1999), selective attention (Mitrofanis and Guillery, 1993), P3 generation, and modified memory performance (Hammond et al., 1987; Dierks et al., 1994; Frodl-Bauch et al., 1999; Potter et al., 2000). The GRM8 gene encodes a presynaptic autoreceptor involved in modulating neuronal excitability by inhibiting glutamate release at the synapse (Schoepp, 2001). Hence, these findings implicate CHRM2 and GRM8 in the generation and modulation of these oscillations during the P3 response to target stimuli. GABAergic, cholinergic, and glutamatergic system interactions have been proposed to underlie these rhythms and P300 (Frodl-Bauch et al., 1999). Thus, the genetic underpinnings of these oscillations influence the excitability in neural networks.
