Using Marijuana in Adolescence May Further Alter Brain Structure

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Long-term marijuana use and altered brain structure may hinge on the age at first use, according to new research published in the Proceedings of the National Academy of Sciences of the United States of America.

Francesca M. Fibey, PhD, of the School of Behavioral and Brain Sciences and the University of Texas, and colleagues studied the effects of delta-9 tetrahydrocannabinol (THC) on the brain using MRI techniques. The researchers evaluated 110 adults, 48 of which were users and 62 non-users, using whole brain MRI, resting state functional MRI and diffusion tensor imaging to measure gray matter volume, functional connectivity, and structural connectivity.

Long-term users showed a reduced gray matter volume and increased structural and functional connectivity in the orbitofrontal cortex (OFC), however most significant is the finding that early onset of use may be associated with increased functional connectivity in white matter, while long-term use may contribute to decreased structural connectivity.

"Another important point from the paper is that there was a direct relationship with age of onset. So those who began regular use at adolescence seemed to have the greater effects on these brain measures, including greater volume reduction," Filbey told Medscape Medical News.

Imaging results showed that users had lowers gray matter volume in the right middle orbitofrontal and left superior orbitofrontal gyri than non-users, and users had a higher resting functional connectivity in the left and right OFC and left and right temporal gyri.

Younger age at first use was also associated with higher OFC functional connectivity. 

Man smoking marijuana
Using Marijuana in Adolescence May Further Alter Brain Structure

The link between long-term marijuana use and altered brain structure may depend on the age at first use and duration of use, new imaging research suggests.

A study of 110 adult participants show that long-term marijuana users have reduced gray matter volume and increased structural and functional connectivity in the orbitofrontal cortex (OFC), a brain region responsible for decision making, compared with nonusers. The findings also suggest that early onset of regular marijuana use may be associated with increased functional connectivity in white matter, whereas long duration of marijuana use might be tied to decreased structural connectivity.

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