Fig. 1. Group differences (analysis of covariance) for all-night power in (A) HF band and (B) LF:HF ratio. Mean values are adjusted for ambient stress at baseline and wakefulness during sleep. HF power is represented as milliseconds squared/hertz, and LF:HF ratio is represented as the ratio of LF to HF spectral power. Error bars represent SD. *p < .05.