Fig. 4. Spectral analysis of electroencephalogram data reveals a shift in power induced by methylphenidate during a continuous target-controlled infusion of propofol. Warm colors (e.g. , red ) represent higher power at a given frequency, whereas cool colors (e.g. , blue ) represent lower power. (A ) A representative spectrogram computed from a rat in the awake state shows predominance of θ power (4–8 Hz). (B ) A representative spectrogram computed from a rat during propofol general anesthesia shows predominance of δ power (less than 4 Hz) before and after administration of normal saline. However, administration of methylphenidate (5 mg/kg IV) promptly reduced δ power, and increased θ (4–8 Hz) and β power (12–30 Hz), providing evidence for a new arousal state distinct from the baseline awake state. MPH = methylphenidate.