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Marijuana use may reduce neural response to reward anticipation

Recent findings show an association between marijuana use in young adulthood and decreased neural response in the nucleus accumbens during reward anticipation.

“What we saw was that over time, marijuana use was associated with a lower response to a monetary reward,” study researcher Mary Heitzeg, PhD, of University of Michigan, Ann Arbor, said in a press release. “This means that something that would be rewarding to most people was no longer rewarding to them, suggesting but not proving that their reward system has been ‘hijacked’ by the drug, and that they need the drug to feel reward — or that their emotional response has been dampened.”

Mary Heitzeg

To determine if marijuana use among young adults affected nucleus accumbens activation during reward anticipation, researchers evaluated 108 young adults from the Michigan Longitudinal Study, an ongoing study of youth at high risk for substance use disorder. Study participants underwent functional MRI scans at age 20 years, 22 years and 24 years. Marijuana and other drug use was determined via self-reports collected annually since age 11 years.

Greater marijuana use was associated with later reduced activation in the nucleus accumbens during reward anticipation (P = .01).

In a cross-lagged model including previous and concurrent cigarette use, the effect of marijuana use from age 22 years to 24 years remained significant (P = .005) and the effect of cigarette use was insignificant.

“Some people may believe that marijuana is not addictive or that it's ‘better’ than other drugs that can cause dependence,” Heitzeg said in the release. “But this study provides evidence that it's affecting the brain in a way that may make it more difficult to stop using it. It changes your brain in a way that may change your behavior, and where you get your sense of reward from.” – by Amanda Oldt

Disclosure: The researchers report no relevant financial disclosures.