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    Pot Habit Early in Life May Alter Brain

    Regular marijuana users who started smoking before 16 had marked differences on MRI scans

    WebMD News from HealthDay

    By Dennis Thompson

    HealthDay Reporter

    FRIDAY, Feb. 26, 2016 (HealthDay News) -- Young teens who smoke pot may wind up with brains that look strikingly different from those who start using marijuana later in their lives, a new study reports.

    Early pot use may alter the physical development of a young teen's brain. It seems to obstruct the natural process by which the body eliminates unneeded neurons and synaptic connections, the researchers reported.

    As a result, the brains of people who started smoking pot younger than age 16 tend to have fewer surface wrinkles and folds in the outer layer of the brain, also known as the cerebral cortex, said study lead author Francesca Filbey. She is chair of Behavioral and Brain Sciences at the University of Texas at Dallas' Center for BrainHealth.

    The cortex also tended to be thicker in these early use teens, again suggesting that less development had occurred, the researchers said.

    However, the study cannot definitively prove a cause-and-effect relationship. Filbey said the researchers couldn't rule out that the differences in brain development might drive early marijuana use, rather than vice versa.

    "It could be that perhaps having these altered brain patterns is what led to the greater marijuana use," she said.

    Still, the difference in brain development might be due to marijuana's influence on dopamine levels in the brain, which could influence how the cortex develops, Filbey added.

    The research team analyzed MRI scans of 42 heavy marijuana users, including 20 considered "early onset" users because they started before age 16. All of the study volunteers began using marijuana during their teens, and continued throughout adulthood. They all reported using pot at least once a week, the researchers said.

    The researchers explained that typical brain development for teens includes a process called "synaptic pruning." During this process, the brain sharpens itself by removing unneeded synapses and neurons. The process results in a thinner cortex that contains more wrinkles and folds on its surface, as well as greater contrast between the brain's gray and white matter.

    In this study, the MRIs revealed that early onset users had thicker cortexes, fewer wrinkles and less gray and white matter contrast, compared to people who picked up their marijuana habit at 16 or older.

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