Fig. 5. Electroencephalographic power (ordinate) plotted as a function of frequency (abscissa) averaged for five rats across states of sleep and wakefulness. During wakefulness (A ) and rapid eye movement (REM) sleep (C ), buprenorphine did not change electroencephalographic power. In contrast, during NREM sleep that occurred after buprenorphine administration (B ) there was a significant increase in electroencephalogram delta power (black horizontal bar above 2.0–3.0 Hz). EEG = electroencephalogram; NREM = nonrapid eye movement.