Summary: Even small amounts of cannabis use in teens can alter gray matter volume in the brain, a new study reports. Researchers report those exposed to cannabis had more gray matter volume in the amygdala and hippocampus, areas of the brain linked to emotional processes and memory development.
Source: Larner College of Medicine.
At a time when several states are moving to legalize recreational use of marijuana, new research shows that concerns about the drug’s impact on teens may be warranted. The study, published in The Journal of Neuroscience, shows that even a small amount of cannabis use by teenagers is linked to differences in their brains.
Senior author and University of Vermont (UVM) Professor of Psychiatry Hugh Garavan, Ph.D., and first author and former UVM postdoctoral fellow Catherine Orr, Ph.D., say this research is the first to find evidence that an increase in gray matter volume in certain parts of the adolescent brain is a likely consequence of low-level marijuana use.
Few studies have looked at the effects of the first few uses of a drug, says Garavan. Most researchers focus on heavy marijuana users later in life and compare them against non-users. These new findings identify an important new area of focus.
“Consuming just one or two joints seems to change gray matter volumes in these young adolescents,” Garavan says.
The new study, part of a long-term European project known as IMAGEN, included 46 kids who reported having used cannabis once or twice by age 14. Their brains showed more gray matter volume in areas where cannabis binds, known as cannabinoid receptors, compared to the kids who didn’t use the drug. The biggest differences in gray matter were in the amygdala, which is involved in fear and other emotion-related processes, and in the hippocampus, involved in memory development and spatial abilities.
Exploiting the advantages of the study’s longitudinal data, the researchers ruled out the likelihood that the cannabis-using kids had pre-existing differences in gray matter thickness or that they had specific personality traits that might correlate with the difference in brain makeup.
“The implication is that this is potentially a consequence of cannabis use,” Garavan says. “You’re changing your brain with just one or two joints. Most people would likely assume that one or two joints would have no impact on the brain.”
What the increased brain matter volume means is unclear.
Typically at that age, Garavan says, the adolescent brain undergoes a “pruning” process, where it gets thinner, rather than thicker as it refines its synaptic connections.
“One possibility is they’ve actually disrupted that pruning process,” Garavan says of the marijuana-using kids.
Garavan spearheaded the IMAGEN project with several European colleagues in 2008 while he was at Trinity College Dublin in Ireland. IMAGEN has collected brain-imaging data from 2,000 children in Ireland, England, France and Germany, starting when they were 14 and continuing through age 23. The goal is to examine the influence of biological, psychological and environmental factors in adolescence on brain development and mental health.
Funding: The study was supported by European Union Joint Programme – Neurodegenerative Disease Research, Swedish Research Council FORMAS, Medical Research Council, National Institute for Health Research Biomedical Research Centre, Maudsley National Health Service Foundation Trust.
Source: Jennifer Nachbur – Larner College of Medicine
Publisher: Organized by NeuroscienceNews.com.
Image Source: NeuroscienceNews.com image is in the public domain.
Original Research: Abstract for “Grey Matter Volume Differences Associated with Extremely Low Levels of Cannabis Use in Adolescence” by Catherine Orr, Philip Spechler, Zhipeng Cao, Matthew Albaugh, Bader Chaarani, Scott Mackey, Deepak D’Souza, Nicholas Allgaier, Tobias Banaschewski, Arun L.W. Bokde, Uli Bromberg, Christian Büchel, Erin Burke Quinlan, Patricia Conrod, Sylvane Desrivières, Herta Flor, Vincent Frouin, Penny Gowland, Andreas Heinz, Bernd Ittermann, Jean-Luc Martinot, Marie-Laure Paillère Martinot, Frauke Nees, Dimitri Papadopoulos Orfanos, Tomáš Paus, Luise Poustka, Sabina Millenet, Juliane H. Fröhner, Rajiv Radhakrishnan, Michael N. Smolka, Henrik Walter, Robert Whelan, Gunter Schumann, Alexandra Potter and Hugh Garavan in Journal of Neuroscience. Published January 14 2019.
Grey Matter Volume Differences Associated with Extremely Low Levels of Cannabis Use in Adolescence
Rates of cannabis use among adolescents are high, and are increasing concurrent with changes in the legal status of marijuana and societal attitudes regarding its use. Recreational cannabis use is understudied, especially in the adolescent period when neural maturation may make users particularly vulnerable to the effects of Δ-9-tetrahydrocannabinol (THC) on brain structure. In the current study, we used voxel-based morphometry to compare grey matter volume (GMV) in 46 fourteen year old human adolescents (males and females) with just one or two instances of cannabis use and carefully matched THC-naïve controls. We identified extensive regions in the bilateral medial temporal lobes as well as the bilateral posterior cingulate, lingual gyri, and cerebellum that showed greater GMV in the cannabis users. Analysis of longitudinal data confirmed that GMV differences were unlikely to precede cannabis use. GMV in the temporal regions was associated with contemporaneous performance on the Perceptual Reasoning Index and with future generalized anxiety symptoms in the cannabis users. The distribution of GMV effects mapped onto biomarkers of the endogenous cannabinoid system providing insight into possible mechanisms for these effects.
Almost 35% of American 10th graders have reported using cannabis and existing research suggests that initiation of cannabis use in adolescence is associated with long-term neurocognitive effects. We understand very little about the earliest effects of cannabis use, however, as most research is conducted in adults with a heavy pattern of lifetime use. This study presents evidence suggesting structural brain and cognitive effects of just one or two instances of cannabis use in adolescence. Converging evidence suggests a role for the endocannabinoid system in these effects. This research is particularly timely as the legal status of cannabis is changing in many jurisdictions and the perceived risk by youth associated with smoking cannabis has declined in recent years.