title: 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.
authors.affiliation: University of Pennsylvania, Department of Psychiatry, Philadelphia, PA 19104, USA. Electronic address: rweth@mail.med.upenn.edu.
authors.forename: Reagan R
authors.initials: RR
authors.lastname: Wetherill
authors.affiliation: University of Pennsylvania, Department of Psychiatry, Philadelphia, PA 19104, USA.
authors.forename: Zhuo
authors.initials: Z
authors.lastname: Fang
authors.affiliation: University of Pennsylvania, Department of Psychiatry, Philadelphia, PA 19104, USA.
authors.forename: Kanchana
authors.initials: K
authors.lastname: Jagannathan
authors.affiliation: University of Pennsylvania, Department of Psychiatry, Philadelphia, PA 19104, USA.
authors.forename: Anna Rose
authors.initials: AR
authors.lastname: Childress
authors.affiliation: University of Pennsylvania, Center for Functional Neuroimaging, Philadelphia, PA 19104 USA.
authors.forename: Hengyi
authors.initials: H
authors.lastname: Rao
authors.affiliation: University of Pennsylvania, Department of Psychiatry, Philadelphia, PA 19104, USA.
authors.forename: Teresa R
authors.initials: TR
authors.lastname: Franklin
mesh_terms: D000328:Adult; D001921:Brain / Q000503:physiopathology*; D005260:Female; D059907:Functional Neuroimaging; D006179:Gyrus Cinguli / Q000503:physiopathology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008385:Marijuana Smoking / Q000503:physiopathology*; D008875:Middle Aged; D009434:Neural Pathways / Q000503:physiopathology*; D012907:Smoking / Q000503:physiopathology*; D014029:Tobacco Use Disorder / Q000503:physiopathology*; D055815:Young Adult
keywords: Cannabis; Dependence; Nicotine; Resting state functional connectivity