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A recent study in Neuropsychopharmacology takes a laboratory look at the impact of acute marijuana effects on human risk taking behavior. Researchers from the Department of Psychiatry & Behavioral Sciences, University of Texas Health Science Center, Houston, TX set out to replicate previous studies that have established a relationship between marijuana use and risky behavior in natural settings.
The present study was designed to examine the acute effects of smoked marijuana on human risk taking, and to identify behavioral mechanisms that may be involved in drug-induced changes in the probability of risky behavior. Using a laboratory measure of risk taking designed to address acute drug effects, 10 adults were administered placebo cigarettes and three doses of active marijuana cigarettes (half placebo and half 1.77%; 1.77%; and 3.58% D9-THC) in a within-subject repeated-measures experimental design. The risk-taking task presented subjects with a choice between two response options operationally defined as risky and nonrisky. Data analyses examined cardiovascular and subjective effects, response rates, distribution of choices between the risky and nonrisky option, and first-order transition probabilities of trial-by-trial data.
Consistent with previous risk-taking studies, shifts in trial-by-trial response probabilities at the highest THC dose suggested a change in sensitivity to both reinforced and losing risky outcomes. Altered sensitivity to consequences may be a mechanism in drug-induced changes in risk taking.
The researchers suggest that THC-induced disruption of the mesolimbic-prefrontal cortical (PFC) network, and a related change in behavioral sensitivity to consequences, may be related to the observed risk-taking patterns. Previous neuroimaging studies of human risky decision making have identified brain structures that function in the evaluation and anticipation of risky and/or uncertain response options; these include mesolimbic, limbic, and specific PFC regions. Importantly, D9-THC impacts neurotransmission in several of these same areas Previous work also suggests that differential sensitivity to reward and punishment is related to individual differences in risk taking. The scientists further suggest that acute marijuana administration may affect both mesolimbic PFC activity and sensitivity to consequences both of which are involved in risk taking/decision making providing a potential mechanism through which marijuana might engender changes in risky behavior. In the absence of more direct neurobiological and behavioral data, the assumptions about THC-related changes in risk taking should be seen as preliminary, and confirmation will require further experimentation. Indeed, determining the acute effects of D9-THC on (a) reinforced and punished behavior and (b) the interaction with specific biobehavioral processes that mediate response to reinforcing and aversive consequences may be an important direction for future studies seeking to understand the relationship between marijuana and risk taking.
Neuropsychopharmacology
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