A validation of event-related FMRI comparisons between users of cocaine, nicotine, or cannabis and control subjects.
OBJECTIVE
Noninvasive brain imaging techniques are a powerful tool for researching the effects of drug abuse on brain activation measures. However, because many drugs have direct vascular effects, the validity of techniques that depend on blood flow measures as a reflection of neuronal activity may be called into question. This may be of particular concern in event-related functional magnetic resonance imaging (fMRI), where current analytic techniques search for a specific shape in the hemodynamic response to neuronal activity.


METHODS
To investigate possible alterations in task-related activation as a result of drug abuse, fMRI scans were conducted on subjects in four groups as they performed a simple event-related finger-tapping task: users of cocaine, nicotine, or cannabis and control subjects.


RESULTS
Activation measures, as determined by two different analytic methods, did not differ between the groups. A comparison between an intravenous saline and an intravenous cocaine condition in cocaine users found a similar null result. Further in-depth analyses of the shape of the hemodynamic responses in each group also showed no differences.


CONCLUSIONS
This study demonstrates that drug groups may be compared with control subjects using event-related fMRI without the need for any post hoc procedures to correct for possible drug-induced cardiovascular alterations. Thus, fMRI activation differences reported between these drug groups can be more confidently interpreted as reflecting neuronal differences.
Murphy
Kevin
K
Department of Psychology, Trinity College Dublin, Dublin 2, Ireland. hugh.garavan@tcd.ie
Dixon
Veronica
V
LaGrave
Kathleen
K
Kaufman
Jacqueline
J
Risinger
Robert
R
Bloom
Alan
A
Garavan
Hugh
H
D000328:Adult; D001921:Brain / Q000098:blood supply* / Q000503:physiopathology*; D001931:Brain Mapping; D003042:Cocaine / Q000494:pharmacology; D019970:Cocaine-Related Disorders / Q000175:diagnosis* / Q000503:physiopathology; D013759:Dronabinol / Q000494:pharmacology; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology*; D005260:Female; D005625:Frontal Lobe / Q000098:blood supply / Q000503:physiopathology; D006179:Gyrus Cinguli / Q000098:blood supply / Q000503:physiopathology; D006439:Hemodynamics / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000706:statistics & numerical data*; D008297:Male; D002189:Marijuana Abuse / Q000175:diagnosis* / Q000503:physiopathology; D008875:Middle Aged; D009538:Nicotine / Q000494:pharmacology; D011597:Psychomotor Performance / Q000502:physiology; D012372:ROC Curve; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology; D015203:Reproducibility of Results; D014029:Tobacco Use Disorder / Q000175:diagnosis* / Q000503:physiopathology
D009538:Nicotine; D013759:Dronabinol; D003042:Cocaine