Decision-making Processes Blunted in Chronic Marijuana Smokers

June 21, 2011

Smoking marijuana affects peoples’ impulsivity, attention, memory, cognition and decision-making abilities. That’s been scientifically proven.

Recent research from Wake Forest Baptist Medical Center draws on the findings of previously published studies to further understanding about how marijuana affects the brains of chronic users, with specific focus on how the drug affects the decision-making process.

These findings are important because they demonstrate a potential, negative side effect of chronic marijuana use. 

“Understanding how marijuana influences the perception of what is ‘negative’ may help explain continued marijuana use and aid in the development of effective strategies for treatment therapies,” said lead author Michael J. Wesley, Ph.D., department of Physiology and Pharmacology at Wake Forest Baptist. “Published data suggests that marijuana use is increasing, both recreationally and medicinally. However, the misperception that it’s harmless is also rising. It’s imperative that we begin analyzing the effects of long term, heavy marijuana use.”

Published by “Psychiatry Research” in the January 2011 issue, Wesley’s study was supported with grants from the National Institute of Drug Abuse (NIDA). Wesley and his co-researchers on the study are attending the annual meeting of the College on Problems of Drug Dependence (CPDD) this week in Florida. Wesley presented preliminary findings from the study last year at the conference and expects that his study and others similar to it will be a topic of discussion this year.

NIDA reported last December that regular marijuana use is on the rise among teenagers, citing an increase of more than 10 percent in students in 8th, 10th and 12th grade. In addition, NIDA’s 2010 Monitoring the Future study surveyed 46,482 students in 396 public and private schools across 48 states and corroborated the results of the National Survey on Drug Use and Health, also released last year.

In the study, researchers observed that marijuana users performed poorly on the Iowa Gambling Task (IGT), which is a complex decision-making task in which participants make choices under ambiguous conditions and win or lose money based on their choices. The IGT goal is to use the feedback of the wins and losses to guide future choices towards safe options that result in winning more and losing less. The early phase of the IGT is particularly important because early exposure to wins and losses aid the development of decision-making strategies that are exploited in later phases of the task.

Sixteen chronic marijuana users and 16 controls, or non users, performed a modified IGT in an MRI scanner. Performance was tracked and functional brain activity in response to early wins and losses was examined. Researchers were looking to see if poor performance of marijuana users was related to differences in brain activity while evaluating the positive and negative information conveyed by wins and losses during the early, strategy development phase of the IGT.

For the control group, after multiple exposures to early large monetary losses, they began to choose safer, less negative options on the task. In contrast, the marijuana users generally failed to alter their selection patterns and continued to make disadvantageous choices throughout the task. The researchers found that this was because marijuana users were less sensitive to the negative feedback during strategy development.

“The marijuana users appear to have a blunted response to losing. They don’t figure out a strategy to avoid monetary losses and this is associated with a decreased functional brain response to the early, negative information that guides the other group to safer choices,” Wesley said. “The bottom line is that it looks like they don’t care as much if they lose.”

Linda J. Porrino, Ph.D., professor and chair of the Physiology and Pharmacology at Wake Forest Baptist, is the senior author and primary investigator of the study. She said one of the aims of the ongoing research in her lab is to understand “the potential harm associated with heavy use of various drugs of abuse, including marijuana.”

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