Effects of marijuana on visuospatial working memory: an fMRI study in young adults
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The effects of marijuana use on visuospatial working memory were investigated in 19–21-year-olds using functional magnetic resonance imaging (fMRI).
Participants were members of the Ottawa Prenatal Prospective Study, a longitudinal study that collected a unique body of information on participants from infancy to young adulthood including: prenatal drug history, detailed cognitive/behavioral performance, and current and past drug usage. This information allowed for the measurement of an unprecedented number of potentially confounding drug exposure variables including: prenatal marijuana, nicotine, alcohol, and caffeine exposure and offspring alcohol, marijuana, and nicotine use. Ten marijuana users and 14 nonusing controls performed a visuospatial 2-back task while fMRI blood oxygen level-dependent response was examined.
Despite similar task performance, marijuana users had significantly greater activation in the inferior and middle frontal gyri, regions of the brain normally associated with visuospatial working memory. Marijuana users also had greater activation in the right superior temporal gyrus, a region of the brain not typically associated with visuospatial working memory tasks.
These results suggest that marijuana use leads to altered neural functioning during visuospatial working memory after controlling for other prenatal and current drug use. This alteration appears to be compensated for by the recruitment of blood flow in additional brain regions. It is possible that this compensation may not be sufficient in more real-life situations where this type of processing is required and thus deficits may be observed. Awareness of these neural physiological effects of marijuana in youth is critical.
KeywordsVisuospatial working memory Marijuana Executive functioning Functional magnetic resonance imaging
Acknowledgments, Disclosure and Conflict of Interest
The manuscript is dedicated to the memory of Barbara Watkinson—a truly dedicated and inspiring researcher. The authors would like to acknowledge the excellent work of The Ottawa Hospital MRI technologists that assisted with this research. The authors would also like to thank the OPPS research associates, Heather Lintell, Robert Gray, and the always cooperative OPPS offspring. The research was funded through an Ontario Research and Development Challenge Fund grant. The authors do not have a financial relationship with the organization that sponsored the research. The authors also have full control of all primary data and agree to allow Psychopharmacology to review the data if requested. All experimentation complies with the current laws of Canada.
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