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morphology

  • by Paul Armentano, NORML Deputy Director April 30, 2018

    Marijuana researchThe frequent use of cannabis is not associated with changes in brain structure, according to data published online ahead of print in the journal Addiction.

    An international team of scientists from Australia, the United Kingdom, and the United States assessed the relationship between habitual cannabis exposure and grey matter volumes in seven regions of the brain – including the thalamus, hippocampus, amygdala, and the nucleus accumbens – in two large population-based twin samples.

    Researchers reported, “[N]ormal variation in cannabis use is statistically unrelated to individual differences in brain morphology as measured by subcortical volume.”

    By contrast, the repeated use of nicotine was positively associated with significantly smaller thalamus volumes in middle-aged males.

    Authors concluded: “This is the largest exploratory analysis integrating brain imaging with self-report cannabis and comorbid substance use data. After correcting for multiple testing, there was no effect of cannabis use on the volume at any subcortical region of interest in young adults or middle-aged males. … In the context of expanding medicalization and decriminalization and the concerns surrounding the consequences of increased cannabis availability, our findings suggest that normal variation in cannabis use is statistically unrelated to brain morphology as measured by subcortical volumes in non-clinical samples.”

    The findings are consistent with those of prior brain imaging studies reporting that cannabis exposure appears to have little to no significant adverse impact upon brain morphology — particularly when compared to the dramatic effects associated with the alcohol exposure.

    The study’s findings fail to replicate those of a well-publicized 2014 paper which alleged that even casual marijuana exposure may be linked to brain abnormalities, particularly in the amygdala.

    Last week, a meta-analysis of 69 separate studies reported that cannabis exposure in adolescents and young adults is not associated with any significant, residual detrimental effects on cognitive performance. The results from a pair of recently published longitudinal twin studies similarly report that cannabis use is not independently associated with any residual change in intelligence quotient or executive function.

    An abstract of the study, “Testing associations between cannabis use and subcortical volumes in two large population-based samples,” appears online here.

  • by Paul Armentano, NORML Deputy Director February 10, 2015

    Study: Marijuana Use Not Associated With Previously Reported Changes In Brain MorphologyIt was less than a year ago when the mainstream media was chock-full of headlines like this one: ‘Brain changes associated with casual marijuana use in young adults, study finds.’ The alarmist headlines were in response to a controversial paper published by researchers at Harvard University in Boston and Northwestern University in Chicago which alleged to have found differences in brain morphology in a cohort of 20 college-age marijuana users as compared to 20 non-users. The study’s investigators attributed the differences to subjects’ cannabis use.

    But a funny thing happened when a team of scientists from the University of Colorado and the University of Kentucky tried to replicate these results in a separate, larger sample (158 participants) of subjects after rigorously controlling for both groups’ use of alcohol.

    They couldn’t.

    Writing in the January 28 edition of The Journal of Neuroscience, authors summarized:

    “[T]his retrospective study examined brain morphology in a sample of adult daily marijuana users (n = 29) versus nonusers (n = 29) and a sample of adolescent daily users (n = 50) versus nonusers (n = 50). Groups were matched on a critical confounding variable, alcohol use, to a far greater degree than in previously published studies.

    We acquired high-resolution MRI scans, and investigated group differences in gray matter using voxel-based morphometry, surface-based morphometry, and shape analysis in structures suggested to be associated with marijuana use, as follows: the nucleus accumbens, amygdala, hippocampus, and cerebellum.

    No statistically significant differences were found between daily users and nonusers on volume or shape in the regions of interest. Effect sizes suggest that the failure to find differences was not due to a lack of statistical power, but rather was due to the lack of even a modest effect.”

    Why the contradictory results? Investigators speculated that previously reported imaging studies failed to adequately control for the impact of alcohol, a substance that “unlike marijuana, … has been unequivocally associated with deleterious effects on brain morphology and cognition in both adults and adolescents.” In other words, researchers theorized that previously reported differences in the brain images of marijuana consumers as compared to non-users were likely because of subjects consumption of booze, not cannabis.

    They concluded, “In sum, the results indicate that, when carefully controlling for alcohol use, gender, age, and other variables, there is no association between marijuana use and standard volumetric or shape measurements of subcortical structures. … [I]t seems unlikely that marijuana use has the same level of long-term deleterious effects on brain morphology as other drugs like alcohol. The press may not cite studies that do not find sensational effects, but these studies are still extremely important.”

    An abstract of the study, “Daily Marijuana Use Is Not Associated with Brain Morphometric Measures in Adolescents or Adults,” is online here.