title: Effects of marijuana on visuospatial working memory: an fMRI study in young adults.
abstract: OBJECTIVE
  The effects of marijuana use on visuospatial working memory were investigated in 19-21-year-olds using functional magnetic resonance imaging (fMRI).
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Psychology, University of Ottawa, Ottawa, ON, K1N 6N5, Canada. asmith@uottawa.ca
authors.forename: Andra M
authors.initials: AM
authors.lastname: Smith
authors.forename: Carmelinda A
authors.initials: CA
authors.lastname: Longo
authors.forename: Peter A
authors.initials: PA
authors.lastname: Fried
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Hogan
authors.forename: Ian
authors.initials: I
authors.lastname: Cameron
mesh_terms: D000367:Age Factors; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D002188:Cannabis / Q000009:adverse effects; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D002189:Marijuana Abuse / Q000378:metabolism / Q000523:psychology*; D008570:Memory, Short-Term / Q000187:drug effects / Q000502:physiology; D011446:Prospective Studies; D011597:Psychomotor Performance / Q000187:drug effects / Q000502:physiology; D013028:Space Perception / Q000187:drug effects / Q000502:physiology; D014796:Visual Perception / Q000187:drug effects / Q000502:physiology; D055815:Young Adult
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