Spatial working memory in heavy cannabis users: a functional magnetic resonance imaging study.
BACKGROUND
Many neuropsychological studies have documented deficits in working memory among recent heavy cannabis users. However, little is known about the effects of cannabis on brain activity.


OBJECTIVE
We assessed brain function among recent heavy cannabis users while they performed a working memory task.


METHODS
Functional magnetic resonance imaging was used to examine brain activity in 12 long-term heavy cannabis users, 6-36 h after last use, and in 10 control subjects while they performed a spatial working memory task. Regional brain activation was analyzed and compared using statistical parametric mapping techniques.


RESULTS
Compared with controls, cannabis users exhibited increased activation of brain regions typically used for spatial working memory tasks (such as prefrontal cortex and anterior cingulate). Users also recruited additional regions not typically used for spatial working memory (such as regions in the basal ganglia). These findings remained essentially unchanged when re-analyzed using subjects' ages as a covariate. Brain activation showed little or no significant correlation with subjects' years of education, verbal IQ, lifetime episodes of cannabis use, or urinary cannabinoid levels at the time of scanning.


CONCLUSIONS
Recent cannabis users displayed greater and more widespread brain activation than normal subjects when attempting to perform a spatial working memory task. This observation suggests that recent cannabis users may experience subtle neurophysiological deficits, and that they compensate for these deficits by "working harder"-calling upon additional brain regions to meet the demands of the task.
Kanayama
Gen
G
Cognitive Neuroimaging Laboratory, Brain Imaging Center, McLean Hospital/Harvard Medical School, 115 Mill St., Belmont, MA 02478, USA.
Rogowska
Jadwiga
J
Pope
Harrison G
HG
Gruber
Staci A
SA
Yurgelun-Todd
Deborah A
DA
D000328:Adult; D000375:Aging / Q000502:physiology; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D002189:Marijuana Abuse / Q000503:physiopathology / Q000523:psychology*; D008570:Memory, Short-Term / Q000187:drug effects / Q000502:physiology*; D008875:Middle Aged; D009044:Motor Cortex / Q000187:drug effects / Q000502:physiology; D013028:Space Perception / Q000187:drug effects / Q000502:physiology*; D014796:Visual Perception / Q000187:drug effects / Q000502:physiology