Brains of young marijuana users respond differently to social exclusion, study finds

Massachusetts General Hospital has revealed previously unrecognized insights into the consequences of marijuana use that alters cognitive functioning in young, frequent users.

Using marijuana recreationally and frequently has an unexpected response from the part of the brain known as the insula, which is responsible for self-awareness and perception, according to the study “Altered Neural Processing to Social Exclusion in Young Adult Marijuana Users,” published in the March issue of Biological Psychiatry: Cognitive Neuroscience and Neuroimaging.

“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,” said Jodi Gilman, a professor at Harvard Medical School and lead author of the study. “But we currently are unable to determine whether these differences in neural processing are a cause or a result of marijuana use.”

In the study, researchers recruited a total of 42 Boston-area college students — 20 students who reported using marijuana up to four times a week as well as 22 students who claimed they had not used marijuana recently. Although the students were initially told that the experiment was about mental visualization, the experiment was actually designed to test responses to social isolation and ostracism. The participants were instructed to take part in a computer module called Cyberball, an online game of catch that was actually programmed to “throw” them the ball only 75 percent of the time, unbeknownst to participants.

The aim of Cyberball was to give participants a sense of social isolation and exclusion by not involving them in the game 100 percent of the time.

The participants were asked to report and imagine the experience, as if it were a game of reality. When the game was over, they were asked about how they felt during the times when they were excluded from play. Images taken using an MRI machine showed there was significant insula activity in the non-marijuana control group and none in the user group.

Gilman said she was unsure of the study’s implications — researchers are still trying to make sense of this information — but believes it has opened a door for further exploration.

“It is hard to speculate whether [the findings] translate to actual differences in social behavior in real-world situations,” she said. “That is definitely an area for future study.”

Barak Caine, a professor in Boston University’s Department of Psychological and Brain Sciences, disagreed with the conclusion of the study, which states that marijuana damages both physical and mental functioning.

“There is not a lot of evidence that [marijuana] damages,” he said. “There might be differences in the way the brain forms, but it’s not a straightforward consensus among scientists.”

Students making the transition to college from high school might be tempted to engage in marijuana use for a variety of reasons. Some smoke out of conformity to social pressures, while others use marijuana to help alleviate academic and personal stress. When asked about whether people of all ages are equally susceptible to the effects that marijuana has on the brain, Gilman said she believed youths are the population most likely to be socially affected by marijuana.

“I think there is a lot of evidence that young people are susceptible to peer influence,” she said. “Throughout adulthood, peer influence dissipates, but [young people] become reliant on peers for social cues and advice.”

Today, “weed culture” has become so embedded in society, especially among the youth, that those who participate in it often naively focus on the benefits of smoking while glossing over its potential negative effects. Caine, however, said he believes that anyone can make bad decisions, not just frequent or infrequent drug users.

“The most common presumption is that heavy drug users, particularly at younger ages, tend towards making incautious decisions,” he said. “Everyone is guilty of it.”