According to a recent study conducted by University of Michigan researchers, long-term marijuana usage is associated with a decrease in the brain’s response time. The study, published in JAMA Psychiatry, brought forth new information about the effect marijuana can have on the brain of a young adult user.

To determine whether marijuana use among young adults prospectively affects nucleus accumbens (NAcc) activation during reward anticipation.

More than 100 young adults were recruited from the Michigan Longitudinal Study, an ongoing study of youth at high risk for substance use disorder and a contrast sample of control families. Participants underwent three consecutive functional magnetic resonance imaging scans at approximate ages of 20 (time 1), 22 (time 2), and 24 (time 3) years. Self-report data on marijuana and other drug use occasions were collected annually since age 11 years old.

The findings of this study indicate that marijuana use is associated with decreased neural response in the NAcc during the anticipation of non-drug rewards. Over time, marijuana use may alter anticipatory reward processing in the NAcc, which may increase the risk for continued drug use and later addiction, the study authors report.

Mary Heitzeg, a University assistant professor of psychiatry and the senior author of the study, said her team’s study is the first longitudinal study about marijuana usage that is not refutable.