Study looks at marijuana's impact on brain

LOUISVILLE, Ky. — Though marijuana is the most commonly used illegal drug in the country, little is definitively known about its impact on the brain.

A study taking place at Indiana University is designed to help change that.

Clinical psychologist Brian O'Donnell and colleague Sharlene Newman are recruiting current and former marijuana users to participate in a study in which their brains will be analyzed for changes in structure and function.

"From animal studies, there's reason to believe it (marijuana use) will affect parts of the brain and also the connections between them, and some of our preliminary studies suggest that is the case," said O'Donnell, a professor in the department of psychological and brain sciences.

The study — funded by a $275,000 grant from the National Institutes of Health — is taking place as marijuana gains acceptance in some parts of the country. Marijuana has been legalized for recreational use in Colorado, Washington state, Alaska and Oregon, and many states now have medical marijuana programs, according to the National Conference of State Legislatures.

"It's being decriminalized, but without knowledge of really its long-term effects on brain structure or function," O'Donnell said.

The Indiana researchers — who will use magnetic resonance imaging to conduct the study — are recruiting 90 people, ages 18-35, to participate in their research. Along with current and past users of marijuana, the study, which is one of the first of its type, will include people who've never used the drug.

"We're comparing the subjects in the different groups," said Newman, who's an associate professor and the director of IU's Brain Imaging Facility. "The group that's never used marijuana is our baseline group."

Former marijuana users are being studied because it's possible that "smoking cannabis causes problems in the brain in terms of structure or in terms of function, but maybe people recover after they stop using it for a little while," he said.

Study participants will undergo a series of brain scans so that the research team can do connectivity analysis.

"Connectivity analysis tells us something about the efficiency of the communication between brain regions," Newman said in an email. "I like to think of the brain as an electrical circuit. If the insulation on the wires is not intact, you can get current leakage resulting in faulty communication. ... If the connections between brain regions are faulty, then the functioning of the brain will be faulty/inconsistent. With the MRI techniques we will use, we will be able to examine the integrity of the insulation."

Prior to brain scanning, participants will undergo tests of perception, thinking and memory and take a questionnaire about problems they may be having, such as hallucinations, O'Donnell said.

In a previous study, the researchers found that connectivity in the brain was altered in cannabis users in a way that seemed to make the brain less efficient, he said.

O'Donnell noted that people who smoke a lot of marijuana in adolescence are at increased risk later in life of developing schizophrenia. But "we don't know whether marijuana smoking causes that. It might be that people who are becoming mentally ill tend to smoke marijuana," he said.

According to the National Institute on Drug Abuse, negative effects of marijuana include altered perceptions and mood, impaired coordination, difficulty with thinking and problem-solving, disrupted learning and memory, and impact on brain development. Marijuana also may affect cardiopulmonary health, according to the institute.

But "what most people don't know is that there hasn't been a lot of research focusing on marijuana — up until very recently in fact — at least (as) to how it affects the brain," said Dr. Francesca Filbey, an associate professor in the School of Behavioral and Brain Sciences at the University of Texas at Dallas.

"There's been a lot more attention toward alcohol, nicotine and other illicit drugs like cocaine," said Filbey. Also, the approaches have varied across studies and the findings have been inconsistent, she noted.