Long-term marijuana use changes brain's reward circuit

In a paper published in Human Brain Mapping, researchers demonstrated for the first time with functional magnetic resonance imaging that long-term marijuana users had more brain activity in the mesocorticolimbic-reward system when presented with cannabis cues than with natural reward cues.

"This study shows that marijuana disrupts the natural reward circuitry of the brain, making marijuana highly salient to those who use it heavily. In essence, these brain alterations could be a marker of transition from recreational marijuana use to problematic use," said Dr. Francesca Filbey, director of Cognitive Neuroscience Research in Addictive Disorders at the Center for BrainHealth and associate professor in the School of Behavioral and Brain Sciences.

Researchers studied 59 adult marijuana users and 70 nonusers, accounting for potential biases such as traumatic brain injury and other drug use. Study participants rated their urge to use marijuana after looking at various visual cannabis cues, such as a pipe, bong, joint or blunt, and self-selected images of preferred fruit, such as a banana, an apple, grapes or an orange.

Researchers also collected self-reports from study participants to measure problems associated with marijuana use. On average, marijuana participants had used the drug for 12 years.

When presented with marijuana cues compared to fruit, marijuana users showed enhanced response in the brain regions associated with reward, such as the orbitofrontal cortex, striatum, anterior cingulate gyrus, precuneus and the ventral tegmental area.

"We found that this disruption of the reward system correlates with the number of problems, such as family issues, individuals have because of their marijuana use," Filbey said. "Continued marijuana use despite these problems is an indicator of marijuana dependence."

The research was funded by the National Institute on Drug Abuse.