Effects of triazolam on brain activity during episodic memory encoding: A PET study

It is well documented that acute administration of the benzodiazepine hypno tic drug triazolam (Halcion (R)) impairs episodic memory encoding. We exami ned the neuroanatomical substrates of this effect in healthy adult voluntee rs using a double-blind, within-subject design. Following oral capsule admi nistration (0.25 mg/70 kg triazolam or placebo), regional cerebral bloodflo w (rCBF) was measured using positron emission tomography (PET) with O-15-H2 O during the performance of semantic categorization, orthographic categoriz ation, and visual fixation (resting) tasks. rCBF associated with episodic m emory encoding was measured by the difference in rCBF during the orthograph ic categorization task relative to that during the semantic categorization task. Results in the placebo condition (n = 9) replicated those of previous nonpharmacological encoding studies (activation in the left prefrontal cor tex, cerebellum, anterior cingulate cortex, temporal cortex, and occipital cortex). Relative to placebo, results in the triazolam condition (n = 6) re vealed significantly impaired memory performance, and deactivation during e ncoding in a subset of areas shown previously to be associated with encodin g (anterior cingulate cortex, cerebellum, and precuneus). Results are discu ssed in relation to triazolam's effects on mnemonic versus attentional proc esses. (C) 2001 American College of Neuropsychopharmacology. Published by E lsevier Science Inc.