Pubdate: Sun, 13 Sep 2015
Source: Varsity, The (CN ON Edu)
Copyright: 2015 The Varsity
Contact:  http://www.thevarsity.ca/
Details: http://www.mapinc.org/media/2663
Author: Andrew Richmond

U OF T PROFESSOR LINKS MARIJUANA, SCHIZOPHRENIA, AND BRAIN DEVELOPMENT

For boys vulnerable to schizophrenia, cannabis use may change brain structure

Dr. Tomas Paus, professor of psychology and psychiatry at the 
University of Toronto, has co-authored a study linking the use of 
marijuana among schizophrenia-prone adolescents to structural changes 
in the brain.

The study examines almost 1,600 subjects, some of whom did, and some 
of whom did not use marijuana before the age of 16. Some subjects had 
a high risk of schizophrenia, and some had a low risk, based on 
polygenic testing (testing numerous genetic locations for traits 
associated with schizophrenia).

The goal was to find the effect of cannabis use on the development of 
the cerebral cortex - the outer layer of brain tissue, which plays an 
important role in perception, memory, language, and consciousness in general.

Among male subjects who had a high risk of developing schizophrenia, 
those who used cannabis during adolescence developed significantly 
thinner cerebral cortices than those who didn't, and the more often a 
subject used cannabis, the more pronounced the effect was. But males 
with a low risk of schizophrenia saw no change to their cerebral 
development as a result of cannabis use, and females at either high 
or low risk were likewise unaffected.

Paus is quick to point out that the study doesn't prove any sort of 
cause-and-effect relationship - there may be some other factor 
affecting cortical thickness that also creates conditions in which a 
youth would be more likely to use marijuana. He does note, however, 
that the thinning is most pronounced in areas of the cortex with more 
cannabinoid receptors, so there is some evidence that cannabis itself 
is at fault.

The ultimate answers to questions of causation, says Paus, lie in 
experimental work, not in work that studies health trends across 
populations like his. But a good first step, he thinks, would be 
longer-term studies with larger samples, to more concretely establish 
the link between cannabis use, cortical development, and schizophrenia.

The current study is nonetheless an important step in exploring the 
development of mental disorders in adolescence, and identifying the 
role of cannabis use in brain development.

Paus is aware that the study has been released into a contentious 
political climate, with three dominant political parties and as many 
positions on marijuana legalization. However, he cautions those who 
would attach any political significance to his results, saying "This 
kind of research does not contribute to policy decisions" - at least 
until it proves more concrete connections between marijuana use and 
mental illness.

This is not to diminish the importance of the research. Paus thinks 
that even if it shouldn't inform policy, this evidence, in 
conjunction with other research showing that "adolescent cannabis use 
increases probability of schizophrenia later in life," should be 
taken seriously by the academic community and the general public, 
especially by those who have significant family histories of mental 
illness, or anything else increasing the risk of such illness, making 
them more susceptible to the dangers the study highlights.
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