Marijuana use prompted changes in brain region involved in reward processing
Each marijuana user was asked to estimate his or her drug intake over a 3-month period, providing the number of days and amount they smoked.
Psychiatric evaluation ruled out the chance that the marijuana users were dependent on the drug, however, the MRI images showed "significant" brain differences.
Compared with the non-smokers, the marijuana users had a larger nucleus accumbens - the brain region involved in reward processing. Additionally, it had an altered shape and structure in the brains of the marijuana users.
And the more marijuana the smokers used, the greater the abnormalities in both the nucleus accumbens and the amygdala, a region involved in emotion.
Dr. Hans Breiter, a co-author of the study, says their findings raise "a strong challenge to the idea that casual marijuana use isn't associated with bad consequences."