By Alex Dobuzinskis
(Reuters) - Daily marijuana use is not associated with brain shrinkage when using a like-for-like method to control for the effects of alcohol consumption on those who both drink and toke up, a new study from Colorado has found.
The study, led by neuroscientists at the University of Colorado at Boulder and published Jan. 28 in the Journal of Neuroscience, points to continued uncertainty about how pot use alters the structure of the brain. Even so, other studies have found the drug has short-term effects on learning and memory.
The latest research comes as access to pot is expanding following 2012 ballot measures in Washington state and Colorado that legalized its recreational use, and voter-approved measures last year to do the same in Alaska and Oregon. The drug remains illegal under federal law.
Kent Hutchison, a clinical neuroscientist at the University of Colorado, Boulder, and the senior author of the study, said his team reviewed a number of scientific papers that showed marijuana causes different parts of the brain to shrink, and his team found the studies were not consistent.
"So far, there's not a lot of evidence to suggest that you have these gross volume changes" in the brain, Hutchison said in a phone interview.
In particular, his study examined a paper released last year by researchers at Northwestern University that identified changes to the nucleus accumbens and the nucleus amygdala, regions of the brain that are key to regulating emotion and motivation, in marijuana users who smoke one to seven joints a week.
Hutchison's team tried to replicate those results by recruiting dozens of adults and adolescents and conducting brain imaging on them, and comparing daily pot users to non-users. But he said they took a different approach to rule out the effects of alcohol.
Hutchison's team closely matched daily pot users with non-users based on their alcohol consumption, to compare people who drank similar amounts, in what researchers believed would best eliminate the influence of alcohol, Hutchison said.
"We found no evidence of differences in volumes of the accumbens, amygdala, hippocampus or cerebellum between daily versus non-users, in adults or adolescents," Hutchison's paper said, referring to parts of the brain.
A researcher from Northwestern could not immediately be reached for comment.
John Hudak, a fellow at the Brookings Institution who examines marijuana policy, said the research shows the limits of scientific understanding on how marijuana affects the brain.
(Reporting by Alex Dobuzinskis in Los Angeles; Editing by Eric Walsh)