Spectrogram and the time domain signature of propofol-induced sedation. (A) Spectrogram shows slow-delta oscillations (0.1 to 4 Hz) and alpha-beta (8 to 22 Hz) oscillations in a volunteer subject receiving a propofol infusion to achieve and maintain a target effect-site concentration of 2 μg/ml, starting at time 0.²⁰  The subject was responding correctly to the verbal but not to click train auditory stimuli delivered every 4-s for the entire 16 min, suggesting that she was becoming sedated.²⁰  The lower and upper white curves are the median and the spectral edge frequencies, respectively. (B) Ten-second electroencephalogram trace recorded at minute 6 of the spectrogram in A.