Opioid blockade improves human recognition memory following physiological arousal

Rationale: States of heightened emotion and arousal, such as those that may occur during crimes or traumatic accidents, can impair human memory. Animal models suggest that such memory alterations may be mediated by opioid neuropeptides. In some experimental paradigms, opioid blockade reverses memory impairments related to arousal. Objectives: The present study evaluated the hypothesis that, under conditions of heightened arousal, opioid blockade would enhance memory in human subjects. Methods: Memory for story information was evaluated among subjects randomized to one of four study groups (two orthogonal study conditions): (1) no arousal + no opioid blockade, (2) no arousal + opioid blockade, (3) arousal + no opioid blockade, and (4) arousal + opioid blockade. Both free recall and recognition memory were assessed. Opioid receptor blockade was achieved using a single oral dose of naltrexone. Results: With heightened arousal, subjects receiving naltrexone performed better than those receiving placebo on tests of total and incidental recognition memory. In contrast, with emotionally neutral stimuli, naltrexone subjects performed worse than placebo subjects. Conclusions: These findings demonstrate that opioid peptides mediate alterations in specific aspects of human memory during heightened emotional states, and help to explain why memories may be selectively deficient under conditions of stress. (C) 2001 Elsevier Science Inc. All rights reserved.