Individual differences in the EEG can be characterized using dimensional and categorical approaches. Although most genetic studies of the human EEG have been dealing with continuous variables such as frequency band power or coherence, other studies took a categorical approach focusing on the identification of distinct EEG types, or variants. This typological approach to the genetics of the human brain function was pioneered by F. Vogel, who has identified several specific discrete EEG variants including low-voltage (N), low-voltage borderline (NG); monotonous alpha waves (R); occipital fast alpha-variants (BO); fronto-precentral beta-groups (BG), and diffuse beta-waves (BD) (Vogel, 1970a). Most of these variants are peculiar enough to be distinguished by visual analysis, although quantitative measures were also proposed.
