Marijuana may disrupt brain development
The term pot-head takes on new
meaning with a study that suggests adolescents and young adults who
smoked a lot of marijuana are more likely than non-users to have
disrupted brain development. Using brain scans, researchers found
abnormalities in areas of the brain that interconnect brain regions
involved in memory, attention, decision-making, language and executive
functioning skills.
The findings are of particular concern because adolescence is a
crucial period for brain development and maturation, the researchers
note. “Studies of normal brain development reveal critical areas of the
brain that develop during late adolescence, and our study shows that
heavy cannabis use is associated with damage in those brain regions,”
said study leader Manzar Ashtari of the Children’s Hospital of
Philadelphia.
 The findings – detailed in the Journal of Psychiatric Research – are
considered preliminary, however, and more research is needed to confirm
the work.
The study
This is not the first research to suggest marijuana damages the
brain. In previous reseach involving memory skill tests, subjects who’d
smoked too much did poorly. But brain imaging can reveal specifics. In
an admittedly small study, Ashtari and colleagues performed imaging
studies on 14 young men (average age 19) from a residential drug
treatment centre in New York State, as well as 14 healthy men of the
same age.
The 14 subjects from the drug treatment centre all had a history of
heavy cannabis use during adolescence. On average, they had smoked
marijuana from age 13 till age 18 or 19, and reported smoking nearly 6
marijuana joints daily in the final year before they stopped using the
drug.
The brain scans measured water movement through brain tissues. “The
abnormal patterns of water diffusion that we found among the young men
with histories of marijuana use suggest damage or an arrest in
development of the myelin sheath that surrounds brain cells,” Ashtari
said.
Myelin provides a coating around brain cells similar to insulation
covering an electrical wire. If myelin does not function properly,
signalling within the brain may be slower. Myelin gives its colour to
the white matter of the brain, and covers the nerve fibres that connect
different brain regions.
“Our results suggest that early-onset substance use may alter the
development of white matter circuits, especially those connections among
the frontal, parietal and temporal regions of the brain,” Ashtari said.
“Abnormal white matter development could slow information transfer in
the brain and affect cognitive functions.”
Ashtari pointed out shortcomings in the study, however. For one, it
involved a small number of subjects. Also, five of the 14 subjects with
heavy cannabis use also had a history of alcohol abuse, which may have
contributed an effect.
“Further research should be done to investigate the relation between
repeated marijuana use and white matter development,” Ashtari said.
“However, our work reinforces the idea that the adolescent brain may
be especially vulnerable to risky behaviours such as substance abuse,
because of crucial neural development that occurs during those years.”
The work was funded by the National Institute of Mental Health.
- LiveScience
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