Effort Expenditure and Cannabis Use: Testing the Amotivational Hypothesis

Abstract

Cannabis is the most commonly used illicit drug in the US and appears to have an indirect effect on dopamine (DA) output in the mesolimbic projection, a circuit implicated in reward processing and effort expenditure. Thus, some have suggested that cannabis use might be associated with aberrant effort-based decision making. The most popular theory positing changes in motivation due to cannabis use is the amotivation syndrome hypothesis, which suggests that chronic cannabis use results in impaired executive functioning, arousal, and affective reactivity leading to reduced capacity for goal-directed behavior other than drug seeking. However, only one study has examined this among cannabis users, and the results suggested no difference between cannabis and non-cannabis users. Further, other studies suggest greater effort expenditure among the substance using groups compared to controls. The current study extends these findings by examining the relation between cannabis use and effort-related decision making in a sample of college students. Cannabis using (n = 25) and non-cannabis using (n = 22) students completed the Effort Expenditure for Rewards Task (EEfRT), in which participants choose between a ‘hard’ task that requires pressing a button 100 times with the nondominant little finger for a large sum of money (high effort/high reward) or an ‘easy’ task that requires pressing a button 30 times with the dominant index finger for a smaller sum of money (low effort/low reward). Results were then compared between the cannabis and non-cannabis using groups. On average, participants selected the hard trials 46% of the time (SD = 19%). Participants successfully completed the hard trials 74% of the time (SD 29%), while they completed the easy trials 97% of the time (SD = 6%). No participant selected only hard or easy trials during the duration of the task. Cannabis users (M=41.40, SD=3.55) completed significantly fewer trials compared to nonusers (M=43.64, SD=3.74). Further, Nonusers (M=26.82, SD=10.01) selected easy trials significantly more often compared to cannabis users (M=21.40, SD=8.34), and nonusers (M=99%, SD=2%) also successfully completed easy trials more often compared to cannabis users (M=95%, SD=7%). However, cannabis users and nonusers did not differ in the number of hard trials selected (Cannabis users M=16.82, SD=5.67; Nonusers M=16.82, SD=7.68) or the percentage of successfully completed hard trials out of the total number of hard trials (Cannabis users M=72%, SD=27%; Nonusers M=76%, SD =32%). Both the reward magnitude and probability of reward receipt predicted greater likelihood of selecting a hard trial. In generalized estimating equation models, past month cannabis days and cannabis use disorder symptoms predicted the likelihood of selecting a hard trial, such that greater levels of both cannabis use days and symptoms were associated with an increased likelihood after controlling for reward value, probability, and expected value. The results suggest that college students who use cannabis are more likely to expend effort, even after controlling for the magnitude of the reward and the probability of reward receipt, suggesting the possibility for aberrant reward processing, albeit in the opposite direction of the amotivational syndrome hypothesis.