Figure 4. Effects of NREM period.

Mixed model age- and sex-adjusted means and standard errors for each frequency band by NREM period 1–5 for the control group T1 (black), insomnia T1 (dark gray), and insomnia T2 (light gray). Control group means reflect group effect models. Insomnia group means reflect time-point effect models. For all plots, the y axis is absolute power, and the x axis is NREM period. Group × NREM period interactions were significant for theta and beta bands. Effects of group were higher early in the night for theta power and later in the night for beta power. Effects of time point did not interact significantly with NREM period. NREM = non-rapid eye movement.