Darla Carter

The (Louisville, Ky.) Courier-Journal

LOUISVILLE — 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 in Bloomington 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 is gaining more acceptance in some parts of the country. For example, marijuana has been legalized for adult use in places such as 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. People who choose to use marijuana need to know "what aspects of physical or mental function it might affect."

Recreational use of marijuana is illegal in both Indiana and Kentucky, but Kentucky Gov. Steve Beshear signed a bill into law in April, allowing limited prescribing of cannabidiol, a marijuana derivative. The product, sometimes called cannabis oil, has shown promise in treating children who have epileptic seizures, said Van Ingram, director of Kentucky's Office of Drug Control Policy. In general, efforts to legalize medical marijuana in Kentucky have failed.

The Indiana University researchers — who will use magnetic resonance imaging (MRI) techniques 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 have never used the drug.

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

The users will go through drug screening to verify that they aren't taking other drugs. "We want to study the effects of marijuana, not the effects of marijuana plus cocaine or marijuana plus a lot of alcohol," O'Donnell said.

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 e-mail. "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."

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.

In the new study, the research team will explore whether people who smoke more marijuana over their lives experience more symptoms that are similar to schizophrenics'.

"I think there's a big lack of knowledge about how marijuana might affect the brain and importantly, whether those changes last a long time or not," O'Donnell said. One thing that will be looked at is "whether people who started use earlier in life, say as middle-schoolers, show more problems with mental health or cognition than those who maybe started in college."

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 FrancescaFilbey, 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, director of cognitive neuroscience research in addictive disorders at the Center for BrainHealth at the University of Texas at Dallas. Also, the approaches have varied across studies and the findings have been inconsistent, she noted.

Filbey is the lead author of a recently published study that is similar to the research underway at Indiana University. She and other researchers studied 48 chronic marijuana users and found that they had reduced gray matter volume in the orbitofrontal cortex, a part of the brain associated with addiction, decision-making, inhibition and adaptive learning. However, there was increased connectivity, which suggests that the brain may be able to compensate for that, Filbey said. But it's unclear how the changes that were noted affect marijuana users' behavior, and the researchers didn't find a correlation with users' IQ.

Filbey noted that those who started using marijuana earlier in life had greater abnormalities in the brain.

It's important to learn more about marijuana's impact on the body because changes in legislation suggest that more people in the United States will be using the drug, and existing studies "have suggested there are effects on the brain, but what's most important is that these effects are particularly detrimental when use is initiated during adolescence," Filbey said.