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 effect of low-level marijuana use.
In a first-of-its-kind study, Swinburne cognitive neuroscience lecturer, Dr Catherine Orr, compared the grey matter volume in a group of 46 14-year-olds who had only used cannabis once or twice with a control group of teens who had never used the drug.
Lead scientist Professor Hugh Garavan, from the University of Vermont, said: "Consuming just one or two joints seems".
"Typically, grey matter volume decreases over the course of adolescence".
Grey matter mostly consists of nerve cells, while "white matter" is made up of nerve fibres.
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Smoking cannabis just once as a teenager is enough to alter brain structure, a new study suggests.
"The implication is that this is potentially a outcome of cannabis use", Garavan says.
"Delay or disruption to the typical trajectory of this neural pruning process has been associated with ADHD symptoms and with poor emotional regulation". "Most people would likely assume that one or two joints would have no impact on the brain".
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.
"What's most interesting to me is trying to find out why some people have this response and some people don't, or why some show it to a greater degree than others", she says.