Neuroimaging in cannabis use: a systematic review of the literature.
BACKGROUND
We conducted a systematic review to assess the evidence for specific effects of cannabis on brain structure and function. The review focuses on the cognitive changes associated with acute and chronic use of the drug.


METHODS
We reviewed literature reporting neuroimaging studies of chronic or acute cannabis use published up until January 2009. The search was conducted using Medline, EMBASE, LILACS and PsycLIT indexing services using the following key words: cannabis, marijuana, delta-9-tetrahydrocannabinol, THC, cannabidiol, CBD, neuroimaging, brain imaging, computerized tomography, CT, magnetic resonance, MRI, single photon emission tomography, SPECT, functional magnetic resonance, fMRI, positron emission tomography, PET, diffusion tensor MRI, DTI-MRI, MRS and spectroscopy.


RESULTS
Sixty-six studies were identified, of which 41 met the inclusion criteria. Thirty-three were functional (SPECT/PET/fMRI) and eight structural (volumetric/DTI) imaging studies. The high degree of heterogeneity across studies precluded a meta-analysis. The functional studies suggest that resting global and prefrontal blood flow are lower in cannabis users than in controls. The results from the activation studies using a cognitive task are inconsistent because of the heterogeneity of the methods used. Studies of acute administration of THC or marijuana report increased resting activity and activation of the frontal and anterior cingulate cortex during cognitive tasks. Only three of the structural imaging studies found differences between users and controls.


CONCLUSIONS
Functional neuroimaging studies suggest a modulation of global and prefrontal metabolism both during the resting state and after the administration of THC/marijuana cigarettes. Minimal evidence of major effects of cannabis on brain structure has been reported.
Martín-Santos
R
R
Section of Neuroimaging, PO67 Division of Psychological Medicine, Institute of Psychiatry, King's College London, UK. rmsantos@clinic.ub.es
Fagundo
A B
AB
Crippa
J A
JA
Atakan
Z
Z
Bhattacharyya
S
S
Allen
P
P
Fusar-Poli
P
P
Borgwardt
S
S
Seal
M
M
Busatto
G F
GF
McGuire
P
P
D000328:Adult; D001921:Brain / Q000098:blood supply* / Q000000981:diagnostic imaging; D001931:Brain Mapping / Q000379:methods; D002185:Cannabidiol / Q000494:pharmacology*; D002560:Cerebrovascular Circulation; D003071:Cognition / Q000187:drug effects; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D002189:Marijuana Abuse / Q000175:diagnosis*; D009483:Neuropsychological Tests / Q000706:statistics & numerical data; D017397:Prefrontal Cortex / Q000187:drug effects / Q000378:metabolism*; D014055:Tomography, Emission-Computed / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D055815:Young Adult
D002185:Cannabidiol