Neurophysiology of motor function following cannabis discontinuation in chronic cannabis smokers: an fMRI study.

The objective of this study was to identify the differences in cerebral activation between chronic cannabis smokers and controls in response to finger sequencing. We hypothesized that attentional areas related to motor function as well as primary and supplementary motor cortices would show diminished activation in chronic cannabis smokers. Nine cannabis smokers and 16 controls were included in these analyses. Scanning was performed on a GE 1.5T scanner. Echo planar images and high-resolution MR images were acquired. The challenge paradigm included left and right finger sequencing. Group differences in cerebral activation were examined for Brodmann areas (BA) 4, 6, 24, and 32 using ROI analyses in SPM. Cannabis users, tested within 4-36 h of discontinuation, exhibited significantly less activation than controls in BA 24 and 32 bilaterally during right- and left-sided sequencing and for BA 6 in all tasks except for left-sided sequencing in the left hemisphere. There were no statistically significant differences for BA 4. None of these regional activations correlated with urinary cannabis concentration and verbal IQ for smokers. These results suggest that recently abstinent chronic cannabis smokers produce reduced activation in motor cortical areas in response to finger sequencing compared to controls.