Modafinil increases EEG 3.0-6.75 and 16.75-20.0 Hz activity in NREM sleep (stages 2-4) in Val/Val genotype but has no effect in Met/Met genotype. Top panel: In each frequency bin between 0.0-20.0 Hz, EEG power (C3A2 derivation) after modafinil was expressed as a percentage of the corresponding values after placebo (horizontal dashed line at 100%). Val/Val genotype: black line (n = 10); Met/Met genotype: gray line (n = 12). Means ± SEM are plotted for each 0.25 Hz bin. Black triangles indicate frequency bins which differed in the Val/Val genotype between modafinil and placebo (P < 0.05, paired 2-tailed t-tests). No significant differences were observed in the Met/Met genotype. Bottom panel: Significant (P < 0.05, black) and non-significant (P > 0.05, white) F-values of genotype × treatment interaction in 3-way mixed-model ANOVA with between-subjects factor genotype (Val/Val, Met/Met) and within-subjects factors condition (baseline, sleep deprivation) and treatment (placebo, modafinil).