Chronic smokers: Marijuana's long-term effects on the brain

Researchers used MRI to show that chronic marijuana users had increased brain connectivity but also reduced orbitofrontal cortices – a part of the brain used in decision making.

The study, published in Proceedings of the National Academy of Sciences, used 50 participants who were long-term marijuana smokers and who smoked the drug three times a day, on average.

For the analyses, the brains of these participants were compared with non-marijuana smokers. To rule out other confounding influences, the user and non-user groups were matched for age, gender, ethnicity, and alcohol and smoking usages.

The researchers used magnetic resonance imaging (MRI) to analyse the brains of the participants.

The chronic marijuana users had reduced orbitofrontal cortices, the front part of the brain just behind the eyes. The orbitofrontal cortex is associated with addiction as well as decision making and subsequent reward release.

In contrast, chronic marijuana use was also associated with higher brain connectivity at first, but a gradual decline in connectivity overtime.

And while the increased connectivity peters out after 6-8 years of chronic use, users still retained higher connectivity than healthy non-users. The earlier the person began using marijuana, the more intense the increase in brain connectivity.

The researchers hypothesised that this increased connectivity is the brain’s way of compensating for the reduction in other areas.

This increased connectivity might help to disguise the users’ degraded orbitofrontal cortex and give an outward impression of normality.

This study is one in a short list of long-term studies on the effects of marijuana usage. Further studies have to be conducted to determine whether the brain can re-develop the damaged orbitofrontal cortex.

And since this study determined only associations, further research might study the direct effects of marijuana on brain health.

Published first on Think Inc.

Feature photograph: Torben Hansen/Flickr

Story source: Science Daily/Center for Brain Health

Research paper: Francesca M. Filbey, Sina Aslan, Vince D. Calhoun, Jeffrey S. Spence, Eswar Damaraju, Arvind Caprihan, and Judith Segall. Long-term effects of marijuana use on the brain. PNAS, November 10, 2014 DOI: 10.1073/pnas.1415297111