Short communicationLong-term heavy marijuana users make costly decisions on a gambling task
Introduction
A recent study in animal models reported that chronic Δ9-tetrahydrocannibinol (THC), the active ingredient in marijuana, produces persistent alterations of functional activity in portions of the prefrontal cortex, homologous to the human orbitofrontal cortex, and amygdala (Whitlow et al., 2003). Although deficits on the performance of memory, attention and executive function tasks, generally associated with the dorsolateral prefrontal cortex and the hippocampus, have been reported in heavy marijuana users (Pope and Yurgelun-Todd, 1996, Fletcher et al., 1996, Heishman et al., 1997, Solowij, 1998, Solowij et al., 2002), few studies have explored the effects of marijuana use on tasks associated with the amygdala and orbitofrontal cortex.
The Iowa gambling task (GT) was designed to examine decision-making deficits exhibited by people with damage specifically to ventral and medial prefrontal cortex (Bechara et al., 1994). In this task, subjects choose cards from four decks, with each choice resulting in monetary wins along with occasional monetary losses. Advantageous decks have small wins, but smaller losses, resulting in an overall gain. Disadvantageous decks have larger wins, but larger penalties, resulting in an overall loss. This task therefore, is thought to simulate real-life decision-making involving uncertainty, rewards, and punishments. Patients with damage to prefrontal cortex and amygdala, as well as abusers of alcohol, cocaine, heroin, and methamphetamine, all show impairments on the performance of the gambling task (Petry et al., 1998, Bechara et al., 1999, Mazas et al., 2000, Bartzokis et al., 2000, Grant et al., 2000, Bechara et al., 2001, Bechara and Damasio, 2002). Given that chronic THC exposure is associated with persistent decrements in functional activity in medial prefrontal cortex and amygdala in an animal model, the purpose of the present study was to determine if individuals with a history of heavy long-term marijuana use show impairments on gambling task performance. It was hypothesized that marijuana users would exhibit impaired decision-making strategies as compared to individuals with minimal marijuana exposure.
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Subjects
The Institutional Review Board for human subject research at Wake Forest University School of Medicine approved all procedures, and all subjects provided written informed consent to participate in the study. Subjects included in this study were 20 male and female volunteers, 18–45-years-old. Volunteers were assigned to either a cannabis user or control group (both groups: n = 10; eight males and two females). The user group did not significantly differ from the control group with respect to age
Neuropsychological testing
No statistically significant differences were found between long-term heavy marijuana users and controls on the Spielberger state-trait anxiety inventory or beck depression inventory. On the CANTAB, no group differences were found in response latencies on the simple or five stage reaction time tasks. In addition, marijuana users did not make more errors than controls on the pattern recognition and delayed matching to sample tasks. However, there was a trend towards an increase in the total
Discussion
Marijuana users in the present study appear to make decisions on the GT that lead to larger immediate gains, but also higher overall losses (Fig. 1). This suggests that heavy marijuana users may be particularly prone to poor decision-making, a fact that may contribute to continued drug use despite potentially adverse consequences. The GT was designed to mimic real life situations in which rewards and punishments must be weighed concurrently. The poor judgment exhibited by heavy marijuana users
Acknowledgements
CANTAB is available from Cambridge Cognition, Vision Park, Histon, Cambridge, UK. The authors thank Hilary Smith for valuable editorial comments. This research was supported by USPHS grants DA 05911 (CTW), DA 12137 (AL), and DA 10230 (LJP).
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