Changes in electroencephalography (EEG) spectral content between control group (wakefulness and non–rapid eye movement [REM] sleep) and morphine group (wakefulness and sedation). Topographic power maps in representative recordings in a control patient (A) in wakefulness and non-REM sleep and a morphine patient in wakefulness and sedation (B). Color scale indicates normalized values ranging from minimal (−1) to maximal (+1) EEG power. Mean frontal EEG data from 8 control patients (blue) without morphine compared to 10 patients with morphine (red, C). Two-way ANOVAs showed that a significant interaction between conditions (wake and sleep/morphine) and groups (control, morphine) was found in α, β₁, and β₂ powers (P = 0.034, P = 0.042, and P = 0.027, respectively). Data are shown as mean ± 95% CI. *Mean values significantly different between control and morphine groups with a P < 0.05 using Holm–Sidak post hoc test.