Marijuana has been shown to alleviate physical pain, and new research out of Massachusetts General Hospital suggests the drug may also reduce emotional pain in young adult users.

The study, published in the journal Biological Psychiatry: Cognitive Neuroscience and Neuroimaging, focused primarily on the insula — a region of the brain that plays a role in processing emotional pain. Researchers found that experiencing social exclusion elicited different responses in the insula from marijuana users and non-users. This part of the brain is usually active when someone experiences social rejection, but researchers found that the activation of the insula was reduced in marijuana users. Given that little is known about the neuronal events that take place in marijuana users when they are rejected by peers, these findings prompted researchers to wonder whether numbness to social pain leads to or is a result of marijuana use.

"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,” lead author Dr. Jodi Gilman of the MGH Center for Addiction Medicine said in a statement.

For the study, researchers recruited 42 adults between the ages of 18 and 25 from Boston-area colleges: 20 of them said they used marijuana two to four times a week, while the remainder reported never using marijuana. The participants played Cyberball, a virtual computer game of catch that investigates response to social rejection and ostracism. While they played, researchers took MRIs of three brain regions associated with response to social exclusion — the anterior insula, the ventral anterior cingulate cortex (vACC) and the orbitofrontal cortex (OFC).

However, researchers initially told the participants that the purpose of the study was to examine their mental visualization ability. The participants were also told that they were playing the games with two other players when in actuality the computer was responsible for the amount of times the ball was thrown to them. There was a period during the game in which the participant received the ball 75 percent of the time, then there was a second period in which the ball was never thrown to the participant, followed by a third where they were again included in the game.

Since the OFC region of the brain showed no significant activation during the study, researchers analyzed the results of the anterior insula and the vACC. Researchers found that both marijuana users and non-users exhibited the same level of vACC activation, but they displayed different levels of insula activation. The non-using control group’s insula was active, while the marijuana users produced no significant activation, signifying they were less affected by exclusion than those who didn’t use the drug.

Interestingly, researchers found an association between the amount of vACC activation and the levels of peer conformity and suggestibility in marijuana users, not in non-users, suggesting that pot smokers are more susceptible to peer influence. Researchers say this could signify a more immature pattern of brain development, possibly due to marijuana use.

"While we believe this study does indicate that the neural response to social exclusion is different in marijuana users compared to non-using controls, it is hard to speculate whether that translates to actual differences in social behavior in real-world situations,” Gilman said.

While marijuana’s effect on the brain is not fully understood, past research has shown that marijuana use can alleviate depression, a feeling that can result from social rejection and be traced back to the insula. However, other studies have found that social interactions play a role in whether or not someone decides to use marijuana, suggesting that teens who distance themselves from friends and family are more likely to start using marijuana.

Researchers of the current study say more research is needed to see whether their attitude towards social situations contributes to, or is a result of, marijuana use.

Source: Gilman J, Curran M, Calderon V, Schuster R, Evins A. Altered Neural Processing to Social Exclusion in Young Adult Marijuana Users. Biological Psychiatry: Cognitive Neuroscience and Neuroimaging . 2016.