Learning impairment by Δ(9)-tetrahydrocannabinol in adolescence is attributable to deficits in chunking.
Cannabis is the most popular illicit drug used by adolescents. Yet, there are only a few studies that have examined the effects of cannabis use on learning and memory during this sensitive and important neurodevelopmental stage. Male adolescent Sprague-Dawley rats were treated with Δ(9)-tetrahydrocannabinol (THC, 6 mgkg) daily for 27 days and concurrently trained in a spatial learning and memory task. The chronic effects of cannabis use were specifically examined by assessing animal behaviour during the postacute period (17 h after drug exposure), when minimal acute drug burden is expected to be present. The postacute period is a good model for cannabis use patterns in human adolescents. In addition, we investigated whether the hierarchical organization of working memory (chunking) was impaired by THC-treatment. We show that THC exposure impairs adolescent learning when tested in the postacute period, and that THC impairs the ability of animals to use a chunking strategy.