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

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.

Comorbid Cannabis and Tobacco Use in Adolescents and Adults

“…Tobacco users showed lower connectivity between the PCC and temporal, mPFC (ventral ACC and medial orbitofrontal cortex (mOFC)) and cerebellar (crus I/II) regions and enhanced PCC-cerebellar (bilateral lobule VIIIB) and PCC-mPFC (bilateral frontal poles) connectivity. Cannabis and tobacco users only showed lower PCC-temporal cortex connectivity[40]. The authors proposed that the observed alterations in DMN connectivity were related to addiction more generally and as such might represent an underlying neurobiological vulnerability associated with substance use.…”

Differential associations of combined vs. isolated cannabis and nicotine on brain resting state networks

“…Currently, we are only aware of one study that examined combined vs. unique associations of cannabis and nicotine on resting state networks (RSNs). Using a seed-based analysis that focused on posterior cingulate gyrus (PCG) connections in the brain’s default mode network (DMN), Wetherill and colleagues (2015) found decreased connectivity in users of only cannabis, only nicotine, and concurrent users compared to non-using controls (Wetherill et al 2015). …”

Regular cannabis and alcohol use is associated with resting-state time course power spectra in incarcerated adolescents

“…Corresponding to the literature on cannabis use and resting-state temporal correlation and network spatial maps, cannabis use was associated with the DMN (Bossong et al, 2013; Pujol et al, 2014; Wetherill et al, 2015), a network implicated in self-referential thought, social perspective taking, future thought, and memory (Andrews-Hanna, 2012), and the ECNs (Houck et al, 2013). Interestingly, Pujol et al (2014) showed that the association between activation of the DMN and memory was stronger in young adult cannabis users compared to controls.…”