Marijuana Effects on Human Forgetting Functions

Published 12 Sep 2017

This study investigates and tries to determine which of the individual components of memory are altered by marijuana. It has long been established that acute marijuana use impairs working memory of humans and animals. The previous studies focused on how marijuana affected memory on global terms like word recall, digit recall and paired associate word memory. By employing the delayed matching-to-sample method, the researchers attempted to distinguish whether acute marijuana smoking altered the delay-dependent and delay-independent components of memory. The study is a first in this field and with the use of human subjects; a similar research was carried out using pigeons and a cholinergic drug.

The experiment was carried out with seven subjects but two were dropped from the experiment as they did not meet the requirements of the study. The subjects were recruited thru newspaper advertisement and were adequately compensated for their participation in the study. The subjects were identified as occasional marijuana users and used one more drug in the past. They were required to not use any other drug during the duration of the experiment as checked by a daily urine analysis. This was necessary to rule out any potential interaction with the marijuana and other drug which may affect the results of the experiment.

The apparatus and materials used in the study consisted of a chamber made of plexiglass for the smoking administration. Subjects were directed to smoke marijuana in predetermined sequence. The subject had an ashtray, a pair of tweezers for smoking and subjects were connected to an oscillometric blood pressure and pulse monitor and a carbon monoxide indicator. The subject was cued by a computer monitor as to the smoking protocol. For the experimental test sessions, the subject worked in a chamber alone with a VGA monitor and mouse. The experimental events and data collection was recorded by remote software.

The subject had two sessions for the experiment, the smoking and the experimental testing with the DMTS tasks. For the behavioral testing procedure, subjects were seated in the designed chamber. A detailed instruction was read to them and they were to work with the VGA monitor and mouse. The software recorded all the responses of the subject in the delayed match-to-sample tasks as well as controlled the sequence and schedule of the tasks. For the marijuana smoking, subjects smoked a placebo, a low dose and a high dose cigarette. Subjects were instructed to smoke, hold their breath, inhale or exhale in different sequences and timing. The number of inhalation and dose was monitored till subjects reached the state of acute marijuana intoxication. Doses were given in ascending order with intervening placebo after each high and low dose. After smoking marijuana subjects were asked to answer a self-report cardiovascular measure that was composed of subjective effects of marijuana.

The results of the experiment showed that the acute administration of smoked marijuana to adult humans produced changes in rates of forgetting but not in initial discriminability. The study found evidence that the impairments were due to the delay interval length of tasks. It was observed that the intoxication of marijuana increased the rate of forgetting functions in all subjects. With the DMTS procedure, the researcher was able to determine the mechanism at which marijuana affected memory performance.

The findings of the study shed light on how marijuana affects the cannabinoid receptors in the hippocampus giving evidence that the hippocampus indeed play a major role in memory functions. Moreover, this study helped identify the different components of human memory that are affected by the drug, thus using marijuana in some medical conditions may not be the bets option as it compromises the memory functioning of the patient. Lastly, the study showed that biological and behavioral aspects interact in memory processes, thus cognitive abilities can be impaired by prolonged marijuana use.

This study as an experiment using human subjects and using a potentially harmful substance has some ethical issues. Considering that subjects volunteered for the experiment but the advertisement as a behavioral research was misleading. Although subjects had prior experience in smoking marijuana, the potential hazard of exposing the subjects to acute marijuana smoking within the six week period carries far greater threat than the objectives of the study. The experiment though had sophisticated apparatus and materials and was innovative in using the delayed-dependent and delayed-independent measures but it is not clear on how they did this.


  • Lane, S., Cherek, D., Lieving, L. & Tcheremissine, O. (2005). Marijuana effects on human forgetting functions. Journal of the Experimental Analysis of Behavior, 83; 1 pp 67-83
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