The electroencephalographic effects of two intravenous sedative/hypnotic drugs, propofol and thiopental, were studied at three stable blood concentrations in 52 normal healthy volunteers. The higher concentration resulted in unresponsiveness (lack of response to auditory/tactile stimuli) in all subjects. This report describes the strong frontal-central rhythms apparent in this state using a quantitative description of oscillatory systems underlying the rhythm. These rhythms occur when sedative drug concentrations are greater than those producing the well-described increase in broadband β-power associated with many sedative drugs. Propofol induces rhythms in the α-range, while thiopental produces rhythms in the β-range. Quasistationary for a period of about 1 h, these rhythms exceed the baseline α-rhythm in power. By their resonant nature, these propofol-induced rhythms are analogous to ‘the classic α-rhythm’, but quantitative characteristics of the underlying oscillatory systems are different. Baseline properties of the oscillatory system underlying the initial resting α-rhythm recover completely as drug concentration decays to negligible values.

At equal sedation, propofol produces the same degree of memory impairment as midazolam. Thiopental has mild memory effects whereas fentanyl has none. Ondansetron alone has no sedative or amnesic effects.

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