Cannabis, cigarettes, and their co-occurring use: disentangling differences in default mode network functional connectivity

Co-occurring cannabis and tobacco use is associated with altered connectivity in the brain's default-mode network (DMN). Using resting-state functional MRI, researchers compared DMN connectivity in four groups: cannabis-dependent nonsmokers, cannabis-dependent tobacco smokers, tobacco-only smokers, and healthy controls. All substance-using groups showed lower DMN connectivity than controls, with distinct differences in connections involving the cerebellum, medial prefrontal cortex, parahippocampus, and anterior insula. Among cannabis-dependent individuals, stronger connectivity between the posterior cingulate cortex and right anterior insula correlated with longer duration of cannabis use. These findings suggest that both cannabis and tobacco exposure independently and jointly affect DMN function.

Study at a glance

Abstract

Background Resting-state functional connectivity is a noninvasive, neuroimaging method for assessing neural network function. Altered functional connectivity among regions of the default-mode network have been associated with both nicotine and cannabis use; however, less is known about co-occurring cannabis and tobacco use. Methods We used posterior cingulate cortex (PCC) seed-based resting-state functional connectivity analyses to examine default mode network (DMN) connectivity strength differences between four groups: 1) individuals diagnosed with cannabis dependence who do not smoke tobacco (n=19; ages 20–50), 2) cannabis-dependent individuals who smoke tobacco (n=23, ages 21–52), 3) cannabis-naïve, nicotine-dependent individuals who smoke tobacco (n=24, ages 21–57), and 4) cannabis- and tobacco-naïve healthy controls (n=21, ages 21–50), controlling for age, sex, and alcohol use. We also explored associations between connectivity strength and measures of cannabis and tobacco use. Results PCC seed-based analyses identified the core nodes of the DMN (i.e., PCC, medial prefrontal cortex, inferior parietal cortex, and temporal cortex). In general, the cannabis-dependent, nicotine-dependent, and co-occurring use groups showed lower DMN connectivity strengths than controls, with unique group differences in connectivity strength between the PCC and the cerebellum, medial prefrontal cortex, parahippocampus, and anterior insula. In cannabis-dependent individuals, PCC-right anterior insula connectivity strength correlated with duration of cannabis use. Conclusions This study extends previous research that independently examined the differences in resting-state functional connectivity among individuals who smoke cannabis and tobacco by including an examination of co-occurring cannabis and tobacco use and provides further evidence that cannabis and tobacco exposure is associated with alterations in DMN connectivity.