Brain changes associated
with casual marijuana use in young adults: More 'joints' equal more damage
Date: April 15, 2014
Source: Society for Neuroscience (SfN)
The size and shape of two brain regions
involved in emotion and motivation may differ in young adults who smoke
marijuana at least once a week.
Credit: © EJ White / Fotolia
The size and shape of two brain regions involved in
emotion and motivation may differ in young adults who smoke marijuana at least
once a week, according to a study published April 16 in The Journal of
Neuroscience. The findings suggest that recreational marijuana use may lead to
previously unidentified brain changes, and highlight the importance of research
aimed at understanding the long-term effects of low to moderate marijuana use
on the brain.
Marijuana is the most commonly used illicit drug in
the United States, with an estimated 18.9 million people reporting recent use,
according to the most current analysis of the National Survey on Drug Use and
Mental Health. Marijuana use is often associated with motivation, attention,
learning, and memory impairments. Previous studies exposing animals to
tetrahydrocannabinol (THC) -- the main psychoactive component of marijuana --
show that repeated exposure to the drug causes structural changes in brain
regions involved with these functions. However, less is known about how low to
moderate marijuana use affects brain structure in people, particularly in teens
and young adults.
In the current study, Jodi Gilman, PhD, Anne Blood,
PhD, and Hans Breiter, MD, of Northwestern University and Massachusetts General
Hospital/Harvard Medical School used magnetic resonance imaging (MRI) to
compare the brains of 18- to 25-year olds who reported smoking marijuana at
least once per week with those with little to no history of marijuana use.
Although psychiatric evaluations ruled out the possibility that the marijuana
users were dependent on the drug, imaging data revealed they had significant
brain differences. The nucleus accumbens -- a brain region known to be involved
in reward processing -- was larger and altered in its shape and structure in
the marijuana users compared to non-users.
"This study suggests that even light to
moderate recreational marijuana use can cause changes in brain anatomy,"
said Carl Lupica, PhD, who studies drug addiction at the National Institute on
Drug Abuse, and was not involved with this study. "These observations are
particularly interesting because previous studies have focused primarily on the
brains of heavy marijuana smokers, and have largely ignored the brains of
casual users."
The team of scientists compared the size, shape,
and density of the nucleus accumbens and the amygdala -- a brain region that
plays a central role in emotion -- in 20 marijuana users and 20 non-users. Each
marijuana user was asked to estimate their drug consumption over a three-month
period, including the number of days they smoked and the amount of the drug consumed
each day. The scientists found that the more the marijuana users reported
consuming, the greater the abnormalities in the nucleus accumbens and amygdala.
The shape and density of both of these regions also differed between marijuana
users and non-users.
"This study raises a strong challenge to the
idea that casual marijuana use isn't associated with bad consequences,"
Breiter said.
This research was funded by the National Institute
on Drug Abuse, the Office of National Drug Control Policy, Counterdrug Technology
Assessment Center, and the National Institute of Neurological Disorders and
Stroke.
Story Source: The above story is based on materials provided by Society
for Neuroscience (SfN). Note:
Materials may be edited for content and length.
Journal Reference: Jodi M. Gilman, John K. Kuster, Sang Lee, Myung
Joo Lee, Byoung Woo Kim, Nikos Makris, Andre Van Der Kouwe, Anne J. Blood and
Hans C. Breiter. Cannabis Use is Quantitatively Associated with Nucleus
Accumbens and Amygdala Abnormalities in Young Adult Recreational Users. Journal
of Neuroscience, April 16, 2014 (in press)
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