Resting state functional magnetic resonance imaging reveals distinct brain activity in heavy cannabis users - a multi-voxel pattern analysis

Abstract

Chronic cannabis use can cause cognitive, perceptual and personality alterations, which are believed to be associated with regional brain changes and possible changes in connectivity between functional regions. This study aims to identify the changes from resting state functional magnetic resonance imaging scans. A two-level multi-voxel pattern analysis was proposed to classify male cannabis users from normal controls. The first level analysis works on a voxel basis and identifies clusters for the input of a second level analysis, which works on the functional connectivity between these regions. We found distinct clusters for male cannabis users in the middle frontal gyrus, precentral gyrus, superior frontal gyrus, posterior cingulate cortex, cerebellum and some other regions. Based on the functional connectivity of these clusters, a high overall accuracy rate of 84-88% in classification accuracy was achieved. High correlations were also found between the overall classification accuracy and Barrett Barrett Impulsiveness Scale factor scores of attention and motor. Our result suggests regional differences in the brains of male cannabis users that span from the cerebellum to the prefrontal cortex, which are associated with differences in functional connectivity.

Keywords: Resting state functional magnetic resonance imaging; cannabis; multi-voxel pattern analysis.

Figure 1

Schematic drawing the data processing pipeline for local multi-voxel pattern analysis (MVPA) analysis. NMF: non-negative matrix factorization; SVM: support vector machine; GM: gray matter.

Figure 2

Results of local multi-voxel pattern analysis (MVPA) analysis of resting state functional magnetic resonance imaging (fMRI) data displayed on 3D rendered brain showing distinct clusters between cannabis users and normal controls.

Figure 3

Results of local multi-voxel pattern analysis (MVPA) analysis of resting state functional magnetic resonance imaging (fMRI) data displayed on 2D slices showing 11 clusters with corresponding brain regions. CBM: cerebellum; CGG: cingulate gyrus; FSG: fusiform gyrus; IFG: inferior frontal gyrus; MFG: middle frontal gyrus; PCC: posterior cingulate cortex; PCG: precentral gyrus; SFG: superior frontal gyrus.

Figure 4

Scatter plots between some behavior measurements and mean accuracy rate from support vector machine (SVM) of all the voxels in the map of Figure 2 for cannabis users. Only behavior measurements with significant difference between the two groups were selected, including (a) Barratt Impulsiveness Scale (BIS)-Attention, (b) BIS-Motor, and (c) age of onset of cannabis use; (d) is tetrahydrocannabinol (THC) classification index (TCI) based on THC-COOH/creatine ratio.

Figure 5

Mean functional connectivity between the eleven distinct regions is represented by an adjacent matrix for (a) cannabis users (CB group) and (b) controls (CTL group). The diagonal elements were set to zero to exclude self-connectivity. Higher overall connectivity strength was observed for the CB group, as indicated by their difference (c). The corresponding standard deviation of connectivity between each pair of distinct regions across all subjects is shown in (d). CBM: cerebellum; CGG: cingulate gyrus; FSG: fusiform gyrus; IFG: inferior frontal gyrus; MFG: middle frontal gyrus; PCC: posterior cingulate cortex; PCG: precentral gyrus; SFG: superior frontal gyrus.