This study was designed to identify neuroanatomical locations of propofol's effects on episodic memory by producing minimal and maximal memory impairment during conscious sedation. Drug-related changes in regional cerebral blood flow (rCBF) were located in comparison with rCBF increases during a simple word memory task. Methods: Regional cerebral blood flow changes were assessed in 11 healthy volunteers using H 2 15 O positron emission tomography (PET) and statistical parametric mapping (SPM99)

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... at 600 and 1,000 ng/ml propofol target concentrations. Study groups were based on final recognition scores of auditory words memorized during PET scanning. rCBF changes during propofol administration were compared with those during the word memory task at baseline. Results: Nonoverlapping memory effects were evident: low (n ‫؍‬ 4; propofol concentration 523 ؎ 138 ng/ml; 44 ؎ 13% decrement from baseline memory) and high (n ‫؍‬ 7; 829 ؎ 246 ng/ml; 87 ؎ 6% decrement from baseline) groups differed in rCBF reductions primarily in right-sided prefrontal and parietal regions, close to areas activated in the baseline memory task, particularly R dorsolateral prefrontal cortex (Brodmann area 46; x, y, z ‫؍‬ 51, 38, 22). The medial temporal lobe region exhibited relative rCBF increases. Conclusions: As amnesia becomes maximal, rCBF reductions induced by propofol occur in brain regions identified with working memory processes. In contrast, medial temporal lobe structures were resistant to the global CBF decrease associated with propofol sedation. The authors postulate that the episodic memory effect of propofol is produced by interference with distributed cortical processes necessary for normal memory function rather than specific effects on medial temporal lobe structures.