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| Marijuana |
Regular marijuana use in adolescence,
but not adulthood, may permanently impair brain function and cognition,
and may increase the risk of developing serious psychiatric disorders
such as schizophrenia, according to a recent study from the University
of Maryland School of Medicine.
Researchers hope that the study, published in Neuropsychopharmacology
— a publication of the journal Nature — will help to shed light on the
potential long-term effects of marijuana use, particularly as lawmakers
in Maryland and elsewhere contemplate legalising the drug.
“Over the past 20 years, there has been a
major controversy about the long-term effects of marijuana, with some
evidence that use in adolescence could be damaging,” says the study’s
senior author Asaf Keller, Ph.D., Professor of Anatomy and Neurobiology
at the University of Maryland School of Medicine. “Previous research has
shown that children who started using marijuana before the age of 16
are at greater risk of permanent cognitive deficits, and have a
significantly higher incidence of psychiatric disorders such as
schizophrenia. There likely is a genetic susceptibility, and then you
add marijuana during adolescence and it becomes the trigger.”
“Adolescence is the critical period
during which marijuana use can be damaging,” says the study’s lead
author, Sylvina Mullins Raver, a Ph.D. candidate in the Program in
Neuroscience in the Department of Anatomy and Neurobiology at the
University of Maryland School of Medicine. “We wanted to identify the
biological underpinnings and determine whether there is a real,
permanent health risk to marijuana use.”
The scientists — including co-author
Sarah Paige Haughwout, a research technician in Dr. Keller’s laboratory —
began by examining cortical oscillations in mice. Cortical oscillations
are patterns of the activity of neurons in the brain and are believed
to underlie the brain’s various functions. These oscillations are very
abnormal in schizophrenia and in other psychiatric disorders. The
scientists exposed young mice to very low doses of the active ingredient
in marijuana for 20 days, and then allowed them to return to their
siblings and develop normally.
“In the adult mice exposed to marijuana
ingredients in adolescence, we found that cortical oscillations were
grossly altered, and they exhibited impaired cognitive abilities,” says
Ms. Raver. “We also found impaired cognitive behavioral performance in
those mice. The striking finding is that, even though the mice were
exposed to very low drug doses, and only for a brief period during
adolescence, their brain abnormalities persisted into adulthood.”
The scientists repeated the experiment,
this time administering marijuana ingredients to adult mice that had
never been exposed to the drug before. Their cortical oscillations and
ability to perform cognitive behavioral tasks remained normal,
indicating that it was only drug exposure during the critical period of
adolescence that impaired cognition through this mechanism. The
researchers took the next step in their studies, trying to pinpoint the
mechanisms underlying these changes and the time period in which they
occur.
“We looked at the different regions of
the brain,” says Dr. Keller. “The back of the brain develops first, and
the frontal parts of the brain develop during adolescence. We found that
the frontal cortex is much more affected by the drugs during
adolescence. This is the area of the brain controls executive functions
such as planning and impulse control. It is also the area most affected
in schizophrenia.”
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