Globally, cannabis use has increased lately. In response to the World Health Organization (WHO), about 147 million people, or 2.5% of the world population, devour cannabis. The neurobiological mechanisms of cannabis are yet to be identified, particularly in youth. Cannabis dependence has been related to a wide selection of neurocognitive deficits, equivalent to dangerous behaviors, impaired episodic memory, and weak performance in tasks that require cognitive function.

Study: Altered brain structural and functional connectivity in cannabis users. Image Credit: Lightspring / Shutterstock

Background

Network analyses and morphometry are two methods commonly used to investigate how cannabis affects brain structure and performance. Morphometry evaluation provides insights into the changes within the thickness or volume of brain tissues. Although prior research didn’t find any morphological alterations within the brain of people under high cannabis use, recent evidence contradicts this finding. Recent studies have indicated that cannabis use induces parahippocampal, hippocampal, and lateral atrophy. 

Changes in brain structure and performance may not occur solely resulting from local changes in brain morphology but in addition to alterations in interactions between brain regions. Consequently, many studies developed brain modeling as a network to know the aspects chargeable for the changes in brain function and structural connectivity resulting from chronic cannabis use. 

The vast majority of the large-scale brain network studies have presented heterogeneous findings on how cannabis use affects the brain’s structural and functional connectivity. One previous study evaluated the effect of prolonged cannabis use on axonal connectivity and located compromised structural connectivity within the splenium of the corpus callosum, commissural fibers, and fornix. An increased structural fractional anisotropy was observed in regular cannabis users.

Evaluation of resting-state functional connectivity in cannabis users revealed an enhanced local functional connectivity within the midbrain, ventral striatum, brainstem, and lateral thalamus. A seed-based connectivity evaluation revealed no significant differences in whole-brain functional connectivity between healthy controls and cannabis users. A graph theoretical evaluation also indicated no difference in regional and global properties of resting-state functional networks between non-cannabis and cannabis users.

Densely-connected hubs, generally known as “wealthy clubs,” have been identified in brain networks. These play an important role in information integration across structural and functional brain networks. Nevertheless, not many studies have analyzed the alternations in functional and structural connectivity of brain networks in cannabis users.

In regards to the Study

A recent Scientific Reports study has investigated the alterations in brain functional and structural connectivity in cannabis users and compared the outcomes with healthy controls. The changes within the wealthy club organization in cannabis users were also studied using graph theoretical metrics.

Participants were included within the Human Connectome Project (HCP) dataset, 72 of whom were cannabis users. As well as, 73 healthy individuals were recruited for the control group. Diffusion-weighted images (DWI) and resting-state functional magnetic resonance images (rs-fMRI) were analyzed on this study.

Study Findings

The graphical measures revealed no significant difference in global network measures for either structural or functional networks between cannabis users and healthy controls. Nevertheless, a substantial difference was observed within the clustering coefficient and nodal degree for functional and structural networks between the 2 groups.

Compared to regulate, the structural networks in cannabis users exhibited lower degree centrality inside the left frontal opercular, inferior parietal cortex, posterior opercular cortex, and in right lateral temporal, visual areas, and posterior cingulate. In comparison with the control, an increased structural degree in a number of nodes within the left parieto-occipital regions, including V3CD was observed in cannabis users. Within the context of functional networks, a major decrease within the left frontal operculum was observed in cannabis users.

Processing pipeline for brain structural and functional Network Evaluation. A structural connectome was constructed for every individual using fiber tractography and a parcellation scheme. A functional connectome was also constructed for every individual by calculating the pairwise Pearson’s correlation coefficient of the typical time courses of 379 regions. A graph-theoretical evaluation was then performed to research the topological properties and rich-club organization of the structural and functional brain networks in each healthy controls and cannabis users.

A better clustering coefficient was observed, which indicated elevated local segregation inside the frontoparietal regions that include inferior frontal cortices, frontal opercular, and the premotor cortex structural networks. As well as, some regions within the posterior areas, equivalent to the ventral stream visual cortex and V3CD, exhibited lower coefficients in cannabis users.

In cannabis users, the functional networks were characterised by elevated clustering coefficients within the ventral stream visual cortex, left inferior frontal cortex FST, and area TG dorsal. A lower local functional segregation was observed inside the appropriate hemisphere within the dorsolateral prefrontal cortex, Diencephalon ventral area, and para hippocampal region in cannabis users, in comparison with the control group.

The present study observed that the structurally wealthy club nodes were primarily present within the left bilateral frontal, temporal, and centro-occipital areas, together with deep brain structures for cannabis users and non-users. Interestingly, in comparison with the control group, the structural networks in cannabis users exhibited a better and lower variety of rich-club nodes inside the superior and inferior temporal gyri, respectively. The functional rich-club nodes were mostly distributed inside parietal and posterior areas for each groups. 

Conclusions

The present study investigated the alterations within the brain structural and functional connectivity in cannabis users based on a graph-theoretic evaluation. The brain network of each groups exhibited small-world properties. Regional effects on network segregation and integration measures were observed, which were more outstanding within the insular, frontal opercular, and lateral/medial temporal cortices. Nevertheless, no change in the worldwide properties of the brain network was observed. The rich-club evaluation revealed no significant difference between the 2 groups. In the long run, time-varying changes in resting state functional connectivity patterns in cannabis users have to be studied.