According to researchers at the Center for Brain Health at the University of Texas at Dallas, chronic marijuana use disrupts the natural reward processes within the brain. Their complete study was published in Human Brain Mapping journal and demonstrates with the help of functional magnetic resonance imaging the effects of long-term marijuana use. The brain activity of long-term users is much more active in the mesocorticolimbic reward system when given cannabis cues instead of natural reward cues.
Dr. Francesca Filbey says the study shows that marijuana disrupts the natural reward circuitry of the brain, making brain changes much more apparent in those who use the drug more heavily. The brain alterations could turn out to be a great marker of transition from recreational use to problematic use.
Researchers studied 59 adult marijuana users and 70 non-users, taking into account potential biases such as brain injury and other forms of drug use. Participants were told to rate their urge to use marijuana after looking at visual cues, such as a pipe, a bong, or a joint. They were also shown pictures of fruits that they were allowed to select. Researchers had participants involved in the study fill out self-reports to determine any problems associated with their use of the drug. On average, the participants had used the drug for up to 12 years.
When marijuana cues were compared to fruit cues, marijuana users showed much larger responses in the brain regions known to be associated with reward. This includes the orbitofrontal cortex, striatum, anterior cingulated gyrus, precuneus and the ventral tegmental area.
Filbey says the study found that the disruption of the reward system directly correlates with the number of problems, ranging from family problems or issues directly related to the use of marijuana. When people continue to use the drug in spite of these issues, the problems become an indicator of the dependence on the drug. Research continues to be funded by the National Institute of Drug Abuse.