Early marijuana use might be dulling the effects of social exclusion, a new study examining differences in brain reactions in young adults who either smoke or do not smoke the substance found.
For this study, the researchers at Massachusetts General Hospital (MGH) recruited 42 adults between the ages of 18 and 25 who were from colleges in the Boston area. Twenty participants said they used marijuana two to four times per week, while the remaining 22 participants did not use the substance at all.
All of the participants completed Cyberball, which is a computerized tool that is typically used to assess people's reaction to social exclusion, such as a rejection or ostracism. During the virtual game, the participants had to play catch with two other players, who they did not know was the computer.
At one point during the catch sessions, the players stopped throwing the ball to the participant. This part was supposed to mimic social exclusion. After a few throws, the participant was once again included into the game. The participants did not know what the game was measuring.
MR scans that focused on three sections of the brain tied to social exclusion were taken throughout the game. These sections included the anterior insula, the ventral anterior cingulate cortex (vACC) and the orbitofrontal cortex (OFC).
The researchers found that for the control group of non-marijuana users, there was activation in the vACC and the insula during the exclusion portion of the game. For the users, the researchers found activation in the vACC but none in the insula. The researchers observed no significant activity in the OFC in both groups.
"While we know that peer groups are one of the most important predictors of marijuana use in young adults, we know very little about the neural correlates of social rejection in those who use marijuana," said Jodi Gilman of the MGH Center for Addiction Medicine. "The unexpected reduction in insula response may indicate that marijuana users are less conscious of social norms or have reduced ability to reflect on negative social situations, but we currently are unable to determine whether these differences in neural processing are a cause or a result of marijuana use."
Gilman added despite the study's findings that there are differences between users and non-users, they do not know if these reactions to social exclusion would be the same in real-life situations. A previous study published in Clinical Psychological Science did find that people who reported long-term and frequent use of marijuana were more likely to have social and economic problems later on in life.
The study was published in Biological Psychiatry: Cognitive Neuroscience and Neuroimaging.
