Research at the Mass General is interwoven throughout more than 30 departments, centers and units and is conducted with the support and guidance of the Mass General Research Institute. The Research Roundup is a monthly series highlighting studies, news and events.

Halting Cannabis Use Improves Brain Functions Important for Learning in Adolescents and Young Adults

The forgetful “stoner” student may seem like a tired cliché from teen movies, but it turns out there is scientific evidence that regular cannabis use can have a negative impact on learning and memory in adolescents and young adults.

A recent Mass General research study found that regular cannabis users who stopped for a month showed measurable improvements in learning and memory tests when compared to a similar group who continued using cannabis during the testing period.

Study participants were 88 individuals aged 16-25 who reported using cannabis every week. Both groups – those who continued to use cannabis and those who agreed to stop – completed regular tests in thinking and memory during the study period and provided urine samples to confirm they were following the study protocols.

Researchers found that only those who stopped using cannabis had improved test results during the study, with the most significant improvements coming in the first week. The study was led by Randi Schuster, PhD, director of Neuropsychology at the Mass General Center for Addiction Medicine.

“Our findings provide two pieces of convincing evidence,” says Shuster. “The first is that adolescents learn better when they are not using cannabis. The second – which is the good news part of the story – is that at least some of the deficits associated with cannabis use are not permanent and actually improve pretty quickly after cannabis use stops.”

Could Altering Regulation of the Brain’s Immune Cells Improve Treatment of Neurodegenerative Disease?

An Mass General research team led by Susan Hickman, PhD, and Joseph El Khoury, MD – both of the Rheumatology, Allergy and Immunology Division – proposes that targeting molecules that regulate the activity of microglia – immune cells within the brain – may help treat important neurodegenerative disorders. 

Microglia have three roles: as sentinels, monitoring the brain for unusual changes; as nurturers, promoting the well-being of healthy neurons by clearing out dying cells and debris; and as warriors, defending the brain against infections and toxins by launching an inflammatory attack. In healthy brains, checkpoint molecules keep microglia  from attacking healthy cells. But neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease and amyotrophic lateral sclerosis all feature excessive neuroinflammation.

The Mass General team detailed specific ways that disrupted regulation of microglial function allows initially protective “sentinels” to become out-of-control “warriors” that induce persistent, damaging inflammation. They also identified three potential checkpoint molecules, activation of which may return microglia to their neuroprotective state. More research is needed to understand the genetic patterns that underlie microglia behavior and how these patterns change due to aging and disease.