Teenage pot smokers could be damaging brain structures critical to memory and reasoning, according to new research that found changes in the brains of heavy users.
Research published in the journal Schizophrenia Bulletin showed the brains of young heavy marijuana users were altered in so-called sub-cortical regions — primitive structures that are part of the memory and reasoning circuits. And young people with such alterations performed worse on memory tests than non-using controls, despite the fact that the heavy users had not indulged for more than two years, on average, before the testing.
“We see that adolescents are at a very vulnerable stage neurodevelopmentally,” said Matthew Smith, who led the research team at Northwestern University Feinberg School of Medicine in Chicago. “And if you throw stuff into the brain that’s not supposed to be there, there are long-term implications for their development.”
Smith’s team recruited 44 non-using healthy controls and compared them with 10 people with a history of cannabis use disorder, 15 with a history of cannabis use disorder and a diagnosis of schizophrenia, and 28 with schizophrenia but no past regular use of marijuana. The average age of the people was mid-20s at the time of the testing, but they had been heavy users as teens.
When the team made MRI scans of the three brain regions — the striatum (a collection of bodies key to reward and motivation), the thalamus (the brain’s Grand Central Station for cognition input), and the globus pallidus (involved with both movement and memory) — heavy users showed abnormalities, whether or not they had schizophrenia.
When the groups were given four tests of working memory, like remembering sequences of numbers they’d seen, heavy users, with or without schizophrenia, performed worse than healthy controls and non-using schizophrenics.
“We saw poor performance in the marijuana groups…” Smith explained. “And the younger somebody started using, the more abnormal they looked.”