The scalp electroencephalogram (EEG), the long latency cognitive P300
auditory evoked response (AER), and reaction times were recorded in 10
volunteers sedated with a computer-controlled infusion of propofol to
target plasma concentrations of 0.3, 0.6, 0.9, and 1.2 mu g/mL. The o
bserved mean +/- SE venous plasma concentrations were 0.152 +/- 0.042,
0.372 +/- 0.078, 0.679 +/- 0.104, and 1.065 +/- 0.112 mu g/mL, respec
tively. Scalp EEG topographic mapping revealed that beta(1) activation
was primarily frontal and central with relative sparing of the tempor
al lobes. The P300 response was dramatically reduced by propofol in a
concentration-dependent manner, even though the subjects were consciou
s but clearly sedated. Mean ise reaction times were increased by propo
fol sedation from 347 +/- 35 ms (control) to 391 +/- 48, 460 +/- 70, 5
49 +/- 64, and 622 +/- 120 ms at increasing mean venous plasma propofo
l concentrations. The mean percentage +/- SE of correct responses decr
eased from 98.1 +/- 2.0 (control) to 99.1 +/- 1.7, 87.4 +/- 9.2, 82.8
+/- 12.9, and 69.8 +/- 20.9 at increasing propofol concentrations. Dra
matic alterations in the EEG, P300 response, and reaction times were o
bserved, especially with the higher plasma concentrations which produc
ed conscious sedation.