The most obvious limitation of the present study is that only a few EEG electrodes were included, providing sparse coverage of the scalp. In particular, we did not have electrodes over frontal brain regions, which may have led us to fail to detect some associations, including our failure to replicate the finding of an association between SGIP1 and theta activity obtained in the only other GWAS of EEG parameters (Hodgkinson et al., 2010). Our sample also comprised two different age cohorts: individuals in late adolescence and adults, who ranged considerably in age but were primarily middle-aged. This was required in order to have as large a sample as possible. Although our analyses accounted for differences between age cohorts in mean levels of EEG parameters, it may be that the genetic influences expressed during these different developmental periods are different. Even with the combined age cohorts, our sample was small by current standards (although not by the standards in place when we began this investigation). In addition, to the degree that dominance effects influence these EEG parameters, we will have overestimated
