Summary: Researchers report chronic marijuana users show more brain activity in the mesocorticolimbic reward system when presented with cannabis cues than with natural reward cues.
Source: UT Dallas.
Chronic marijuana use disrupts the brain’s natural reward processes, according to researchers at the Center for BrainHealth at The University of Texas at Dallas.
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.”
Funding: The research was funded by the National Institute on Drug Abuse.
Source: Shelly Kirkland – UT Dallas
Image Source: NeuroscienceNews.com image is credited to McGill University and is licensed CC BY-SA 3.0.
Original Research: Full open access research for “fMRI study of neural sensitization to hedonic stimuli in long-term, daily cannabis users” by Francesca M. Filbey, Joseph Dunlop, Ariel Ketcherside, Jessica Baine, Tyler Rhinehardt, Brittany Kuhn, Sam DeWitt and Talha Alvi in Human Brain Mapping. Published online May 11 2016 doi:10.1002/hbm.23250
fMRI study of neural sensitization to hedonic stimuli in long-term, daily cannabis users
Although there is emergent evidence illustrating neural sensitivity to cannabis cues in cannabis users, the specificity of this effect to cannabis cues as opposed to a generalized hyper-sensitivity to hedonic stimuli has not yet been directly tested. Using fMRI, we presented 53 daily, long-term cannabis users and 68 non-using controls visual and tactile cues for cannabis, a natural reward, and, a sensory-perceptual control object to evaluate brain response to hedonic stimuli in cannabis users. The results showed an interaction between group and reward type such that the users had greater response during cannabis cues relative to natural reward cues (i.e., fruit) in the orbitofrontal cortex, striatum, anterior cingulate gyrus, and ventral tegmental area compared to non-users (cluster-threshold z = 2.3, P < 0.05). In the users, there were positive brain-behavior correlations between neural response to cannabis cues in fronto-striatal-temporal regions and subjective craving, marijuana-related problems, withdrawal symptoms, and levels of THC metabolites (cluster-threshold z = 2.3, P < 0.05). These findings demonstrate hyper-responsivity, and, specificity of brain response to cannabis cues in long-term cannabis users that are above that of response to natural reward cues. These observations are concordant with incentive sensitization models suggesting sensitization of mesocorticolimbic regions and disruption of natural reward processes following drug use. Although the cross-sectional nature of this study does not provide information on causality, the positive correlations between neural response and indicators of cannabis use (i.e., THC levels) suggest that alterations in the reward system are, in part, related to cannabis use.
“fMRI study of neural sensitization to hedonic stimuli in long-term, daily cannabis users” by Francesca M. Filbey*, Joseph Dunlop, Ariel Ketcherside, Jessica Baine, Tyler Rhinehardt, Brittany Kuhn, Sam DeWitt and Talha Alvi in Human Brain Mapping. Published online May 11 2016 doi:10.1002/hbm.23250