Figure 4.

Lower 24-h plasma norepinephrine (NE) and lower slow oscillatory activity (SO: 0.5–1.25 Hz) in the first cycle of sleep correlate with greater subjective sleep disturbance (PSQI) in insomnia. Spearman rank correlations showing significant negative associations between (A) lower mean 24-h plasma NE (data Ln transformed), and (B) lower SO activity in the first cycle of sleep, with higher Pittsburg Sleep Quality Index (PSQI) scores, in participants with insomnia. Data on SO activity in the first cycle of sleep are averaged from nights 2, 3, and 4.