Teenage brains on pot

UWM researcher explores whether exercise can boost brain health of young marijuana users

Krista Lisdahl, assistant professor of psychology, recently was awarded the Presidential Early Career Award for Scientists and Engineers (PECASE), the highest honor bestowed by the U.S. government on professionals in the early stages of their research careers.

What if teenagers with a regular marijuana habit started going to the gym or cycling more? Would it diminish the damage that substance abuse does to their still-developing brains?

That’s the intriguing question behind a sweeping study at the University of Wisconsin-Milwaukee (UWM) that focuses on the relationship of physical activity, marijuana abuse and brain functioning in teens and young adults.

Using three kinds of neuroimaging and multiple measures of fitness among young pot users and nonusing control subjects, the project, led by neuropsychologist Krista Lisdahl, aims to better understand the cognitive consequences of a chronic pot habit before the brain is fully “wired.”

Lisdahl’s study will use explore how indicators of overall physical fitness affects blood flow and neural activity in the brain.

The research also seeks more information about the process of connectivity in the maturing brain and the role of physical activity in that process. The ultimate goal: find an intervention that targets brain deterioration caused by habitual pot use in the early teen years, and perhaps even prevent the damage – or reduce drug abuse.

Regular marijuana use before age 16 has been shown to disrupt development in parts of the brain involved in “complex attention” and “executive functioning” skills – such as the ability to persist over time, make decisions, plan long range and withhold the urge to respond to an emotional cue – all controlled by brain areas that are underdeveloped in this age group.

Lisdahl acknowledges it’s a study that encompasses “many moving parts.”

It has also earned her the Presidential Early Career Award for Scientists and Engineers (PECASE), the highest honor bestowed by the U.S. government on professionals in the early stages of their research careers. Hers is one of 96 awarded nationwide; she was recognized at the White House in July, where she met President Barack Obama. Funding for her award comes from the National Institutes of Health.

A knowledge void

Marijuana is the No. 2 drug of choice among teens, behind alcohol, and its use has been increasing since 2008. But most of the research on effects of marijuana on the brain has been done with adult subjects.

Lisdahl is concerned that teens and young adults may be most at risk for cognitive damage caused by heavy drug use because of the plasticity of their brains – the ability to reorganize connections in order to incorporate learned information.

“Plasticity also presents an opportunity for this age group to incur more damage from substance abuse,” she says. “And we don’t know enough about whether later abstinence will reverse damage yet.”

Scientists have only recently identified the brain receptors for cannabis, and previous research has found marijuana abuse leads to a decreased number of these CB1 receptors over time. That leads to tolerance of the drug’s effects, but also to a list of potential problems in the many other psychological and physiological functions of the body that involve CB1 receptors, including emotional control, mood, appetite, sexual function and pain tolerance.

“CB1 belongs to a large class of receptors that modulate all other neurotransmitters,” she says. “As you damage more and more CB1 receptors, you inflict harm to the entire system. There’s evidence of that happening to a greater extent in teens, but we don’t understand it very well in humans yet.”

Imaging advantage

Lisdahl will use fMRI imaging like this to see brain activity during tasks that test different mental functions, in this case spatial working memory. (From “The Influence of Recency of Use on fMRI Response During Spatial Working Memory in Adolescent Marijuana Users,” available at http://1.usa.gov/N6jzTQ)

She is particularly interested in how both marijuana use and exercise affect the way teens respond in emotional or stressful situations. Calm teenagers can reason almost as well as adults. But introduce a negative emotion, like stress, into the decision-making process and it’s a whole other story. Teens who smoke marijuana heavily find it especially difficult to hold back urges to react when faced with a negative emotion.

“We want to see what that brain communication looks like,” she says. “What would help users rein in their impulsivity?”

To do this, Lisdahl’s team will use functional magnetic resonance imaging (fMRI), which allows the researchers to see specific brain connections as they happen. fMRI identifies the location of brain activity by measuring blood flow as the subject performs tasks requiring them to suppress responses while viewing emotional faces.

The results hold importance for Lisdahl’s study, but also for the study of addiction in general.

“Many addicts say they are more likely to use again in response to a negative emotional trigger,” she says.

Since exercise increases blood flow throughout the body and releases several pro-brain health chemicals, Lisdahl’s study will use fMRI to explore how indicators of overall physical fitness affects blood flow and neural activity in the brain. The research group will record data such as body fat and activity patterns, as well as measuring how effectively young subjects’ bodies are using oxygen.

The researchers hope to answer questions like, “Which body measurement is most related to brain function health?” and “How much activity is needed to mitigate the cognitive deficits of heavy marijuana use by teens?”