GCTA analyses indicated that, although point estimates varied somewhat across endophenotypes, all SNPs on the Illumina array in aggregate (as well as those in LD with the Illumina markers) accounted for a substantial proportion of the variance only in occipital-parietal measures (alpha power and alpha peak frequency). SNP heritability estimates were smaller on the whole for power measures from Cz, especially in the lower frequencies. The large standard errors associated with these estimates make definitive inferences impossible. However, the heritability estimates provide a rough idea of the degree to which common variants influence each endophenotype. In general, they seem to influence alpha power and peak frequency at occipital-parietal sites to a greater degree than the measures from the vertex. Of the measures from Cz, common variants may influence alpha and beta power somewhat more than measures of power in the lowest frequencies, especially the theta band. This difference between higher and lower frequencies may reflect the fact that activity in higher frequencies predominate in the resting EEG, whereas lower-frequency activity is more vulnerable to artifacts and can reflect drowsiness, which
