group, regardless of genotype. Furthermore, the subgroups with minor allele(s) (AG and GG) showed a more diffuse topography with less frontalization than those with the AA genotype, perhaps suggesting a delay in brain maturation. Electrophysiological (Matousek and Petersen, 1973; Gasser et al., 1988a; Gasser et al., 1988b; Dustman et al., 1999; Segalowitz et al., 2010; Chorlian et al., 2015) and neuroimaging (Rubia et al., 2000; Gogtay et al., 2004; Sowell et al., 2004; Yurgelun-Todd and Killgore, 2006; Gogtay and Thompson, 2010; Rubia, 2013) studies of brain development indicate a reduction and focusing of activity, with a shift toward more frontal activity as pruning occurs in the brain (i.e., frontalization). Specifically, ERO theta power gradually decreases as children mature, becoming less in early adolescents, and even less in young adults (Yordanova and Kolev, 1998, 2009; Chorlian et al., 2015; Kamarajan et al., 2015a), as efficiency of cognitive functioning improves with increased phase locking of the theta system and hence neural communication in the course of development (Yordanova and Kolev, 1998, 2009). Therefore, given these suggested findings in the current study, it is possible that the minor alleles of KCNJ6 could be associated with lack of frontalization and/or delayed brain maturation. It
