Title

Title: How white matter is effected by prolonged substantial cannabis use

Background: Although diffusion tensor imaging (DTI) shows changes in white matter of cannabis users, there reason for these changes is not clear.

Methods:
a. This two-year longitudinal study includes a sample of 46 undergraduate students aged 18-20 years. Twenty-three of the students (experimental group) who were selected reported using cannabis at least five times a week, and whose first use of cannabis was prior to the age of 17. The other 23 college students (control group) reported a history of little to no substance use.
b. Participants were asked to read and recall a list of 15 words. This is done a total of five times. Following these five trials, participants were presented with a second list of 15 words as an interference trial, and then asked to freely recall as many words as they can from the first list, and again after a 30-minute delay. This process was repeated two years later.

Results: Cannabis users exhibited significant decreases in fractional anisotropy, particularly in the right hemisphere along the superior longitudinal fasciculus, as well as adjacent to the parietal operculum in the left hemisphere. Cannabis users also report impaired performance in regards to verbal learning.

Conclusion: The study suggests that heavy cannabis use over an extended amount of time negatively changes the microstructure of white matter in the brain, and can inhibit intellectual performance.