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Repeated Delta 9-Tetrahydrocannabinol Exposure in Adolescent Monkeys:
Persistent Effects Selective for Spatial Working Memory 
Verrico CD, Gu H, Peterson ML, Sampson AR, Lewis DA 

American Journal of Psychiatry 171:416-425, 2014

Acute exposure to cannabis produces impairments in working memory, the ability to briefly hold a small amount of information such as a phone number, in mind in order to guide thoughts or behaviors. Chronic cannabis use induces working memory impairments during adolescence (but less reliably during adulthood), and is associated with a lower IQ in adulthood as well as an increased risk of schizophrenia, an illness characterized by working memory deficits.  Working memory performance improves throughout childhood and during adolescence. The ability to retain the features of an object (object working memory) matures faster than the ability to remember its location in space (spatial working memory), suggesting that the latter may be more susceptible to the negative effects of cannabis during adolescence. 

A recent study by Translational Neuroscience Program investigators demonstrated that acute exposure to the main psychoactive ingredient of cannabis, delta 9-Tetrahydrocannabinol (THC), during a time period in adolescence before spatial working memory has reached full capacity selectively impairs spatial but not object working memory.  The research team examined the effect of chronic THC exposure on spatial and object working memory performance in seven pairs of monkeys individually matched for similar baseline cognitive functioning. One member of each pair received THC intravenously five days per week for six months, while the other was administered an inert substance over the same time period.

Consistent with the findings after acute exposure, chronic THC exposure impaired the normal age-related improvement in accuracy on the spatial but not the object working memory task in the adolescent monkeys. This finding suggests that immature cognitive functions are especially vulnerable to the harmful effects of THC, and underscores the significant public health risks associated with the increasing trend of cannabis use among teens. 

Contributors:
Christopher D. Verrico, PhD; Hong Gu, MS; Melanie L. Peterson, BS; Allan R. Sampson, PhD; David A. Lewis, MD (Departments of Psychiatry, Statistics, and Neuroscience, University of Pittsburgh)

The results of this investigation were published in the American Journal of Psychiatry. Click here for a link to the abstract.