The effects of a subanesthetic dose of ketamine on verbal memory in normal volunteers.
BACKGROUND
N-methyl-D: -aspartate (NMDA) glutamate receptor antagonists have been reported to induce schizophrenia-like symptoms in humans, including memory impairments. Although the NMDA receptor has been shown to impair memory acquisition by disrupting long-term potentiation (LTP), limited research has been done on studying the effects of NMDA antagonists on the post-LTP cascade of events implicated in consolidation as measured by administering the drug after the initial learning experience.


OBJECTIVE
The purpose of this experiment was to examine the effect of ketamine on mental status and to identify NMDA antagonist-induced memory deficits by comparing the recall performance of items presented both immediately before and during ketamine infusion.


METHODS
Thirteen normal controls received a 60-min infusion of ketamine in a randomized double-blind, cross-over design. Mental status was evaluated with the Brief Psychiatric Rating Scale and the Clinician-Administered Dissociative States Scale. The first 12-item word list was presented immediately before infusion, and two lists were subsequently presented during the infusion. Verbal memory performance was assessed by measuring the delayed cued recall of each list 30 min after its presentation.


RESULTS
At the beginning, subjects experienced perceptual and reality distortion symptoms, followed later by mild subjective effects. Ketamine significantly reduced the delayed recall of words presented immediately before, but not during, drug infusion. Ketamine-induced decrements in verbal recall correlated significantly with plasma ketamine levels.


CONCLUSIONS
This study characterizes the behavioral effects associated with ketamine and suggests that ketamine decreases verbal memory performance by interfering with early consolidation processes.
Parwani
Arti
A
Maryland Psychiatric Research Center, University of Maryland School of Medicine, P.O. Box 21247, Baltimore, MD 21228, USA.
Weiler
Martin A
MA
Blaxton
Teresa A
TA
Warfel
Dale
D
Hardin
Michael
M
Frey
Kristin
K
Lahti
Adrienne C
AC
D000328:Adult; D003071:Cognition / Q000187:drug effects; D018592:Cross-Over Studies; D004311:Double-Blind Method; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D005260:Female; D006801:Humans; D007649:Ketamine / Q000097:blood / Q000494:pharmacology*; D008297:Male; D008568:Memory / Q000187:drug effects*; D011939:Mental Recall; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors*; D014706:Verbal Learning / Q000502:physiology*
D018691:Excitatory Amino Acid Antagonists; D016194:Receptors, N-Methyl-D-Aspartate; D007649:Ketamine