According to research published in Experimental and Clinical Psychology, the drug ketamine impairs certain memory processes, but not others.
The research was conducted by Michelle R. Lofwall, Roland R. Griffiths, and Miriam Z. Mintzer of the John Hopkins University School of Medicine.
Ketamine is typically used as an anesthetic in veterinary and human medicine, but sub-anesthetic doses of ketamine produce a psychedelic experience. Because of these effects, sub-anesthetic doses ketamine are often used recreational and have also been utilized in the treatment of alcoholism and other addictions.
“Pharmacologically, ketamine acts predominately as a noncompetitive antagonist at N-methyl-D-aspartic acid (NMDA) glutamate-type receptors,” explained Lofwall and his colleagues, meaning that ketamine blocks the action of other chemical signals that interact with NMDA glutamate receptors. These receptors are prominent in the cerebral cortex and “are believed to play a key role in learning and memory.”
In their study, Lofwall and her colleagues administered various doses of ketamine to 18 healthy adult volunteers who had no prior experience with ketamine. After being injected with one of two doses of ketamine or a placebo, the volunteers completed a number of different tasks designed to measure their free recall, recognition memory, source memory, metamemory, and working memory. Their psychomotor performance was also analyzed.
“Ketamine significantly and selectively impaired free recall encoding processes while sparing retrieval processes; however, there were no significant drug effects on other episodic memory tasks (recognition and source memory), nor were there significant effects on metamemory,” according to Lofwell and her colleagues.
In other words, ketamine impairs the ability to form new memories, but does not appear to have a major impact on the ability of the brain to recall or recognize memories that have already been formed in the brain. Other drugs, such as alcohol and benzodiazepines, have a similar effect on ability to form new memories.
The specific impairments caused by ketamine highlight one of its malicious uses. Due to the fact that it can prevent the formation of new memories and slows psychomotor performance, ketamine is sometimes used as a date-rape drug.
“Furthermore, in conjunction with previous studies of drugs with different mechanisms of actions, the observed selectivity of effects enhances understanding of the pharmacological mechanisms underlying memory, attention, psychomotor performance, and subjective experience.”
Lofwall, M.R., Griffiths, R.R. & Mintzer, M.Z. (2006). Cognitive and subjective acute dose effects of intramuscular ketamine in healthy adults. Experimental and Clinical Psychopharmacology, Vol 14, No 4: 439-449.