• David J LaPorte, Teresa A Blaxton, Tamara Michaelidis, Donald U Robertson, Martin A Weiler, Carol A Tamminga, and Adrienne C Lahti.
• Department of Psychology, Indiana University of Pennsylvania, Uhler Hall, Indiana, PA 15705-1068, USA. laporte@iup.edu
• Psychopharmacology (Berl.). 2005 Jul 1; 180 (3): 385-90.

RationaleN-methyl-D-aspartate (NMDA) receptor antagonists (e.g., PCP, ketamine) have been shown to impair learning/memory. Well documented in animal models, only limited research in humans has been reported. Findings to date are similar to results of animal studies; however, antagonists are typically administered before the learning experience. This may be problematic as memory failure could be secondary to inattention induced by the psychotomimetic effects of these drugs and/or alterations in sensory processing which can degrade the quality of the stimulus, thereby affecting the accuracy of recall.ObjectiveThe objective of the study is to compare the effects of ketamine vs placebo on recall for words when administered after stimulus presentation.MethodsIn this double-blind crossover study, 24 normal controls were given bolus injections of ketamine (0.3 mg/kg) or placebo. Immediately prior to infusion, subjects were administered a verbal memory test. Delayed recall was measured 45 min postinfusion. Mental status changes were assessed using the Brief Psychiatric Rating Scale.ResultsSubjects experienced a significant increase in psychiatric symptoms that peaked at 20 min. Results indicate no differences between the drug and placebo conditions for the memory task. However, reminiscence (i.e., recall of previously unrecalled items with repeated testing) was significantly reduced following ketamine administration compared to placebo.ConclusionsFindings suggest that aspects of memory consolidation are affected by drugs that interfere with NMDA receptor function.

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