Increased interhemispheric coherence has been a feature of EEG in alcoholism; when associated with increased depressiveness, it has been suggested to involve GABAergic and/or glutamatergic neurotransmission. Winterer et al. (2003c) revealed that three exonic variants of a GABAB receptor gene influence cortical synchronization (coherence). In the COGA study, significant linkage for theta (6–7 Hz) interhemispheric coherence at parieto-occipital regions led to significant association with several single nucleotide polymorphisms (SNPs) in GABRA2. Another significant linkage peak for theta (6–7 Hz) centroparietal coherence was significantly associated with SNPs in CHRM2, a cholinergic muscarinic receptor gene (Porjesz and Rangaswamy, 2007; Rangaswamy and Porjesz, 2008b).
