title: An MRI study of white matter tract integrity in regular cannabis users: effects of cannabis use and age.
abstract: Conflicting evidence exists on the effects of cannabis use on brain white matter integrity. The extant literature has exclusively focused on younger cannabis users, with no studies sampling older cannabis users.
  
  
  
  We recruited a sample with a broad age range to examine the integrity of major white matter tracts in association with cannabis use parameters and neurodevelopmental stage.
  
  
  
  Regular cannabis users (n = 56) and non-users (n = 20) with a mean age of 32 (range 18-55 years) underwent structural and diffusion MRI scans. White matter was examined using voxel-based statistics and via probabilistic tract reconstruction. The integrity of tracts was assessed using average fractional anisotropy, axial diffusivity and radial diffusivity. Diffusion measures were compared between users and non-users and as group-by-age interactions. Correlations between diffusion measures and age of onset, duration, frequency and dose of current cannabis use were examined.
  
  
  
  Cannabis users overall had lower fractional anisotropy than healthy non-users in the forceps minor tract only (p = .015, partial eta = 0.07), with no voxel-wise differences observed. Younger users showed predominantly reduced axial diffusivity, whereas older users had higher radial diffusivity in widespread tracts. Higher axial diffusivity was associated with duration of cannabis use in the cingulum angular bundle (beta = 5.00 × 10(-5), p = .003). Isolated higher AD in older cannabis users was also observed.
  
  
  
  The findings suggest that exogenous cannabinoids alter normal brain maturation, with differing effects at various neurodevelopmental stages of life. These age-related differences are posited to account for the disparate results described in the literature.
authors: Graduate School of Medicine, University of Wollongong, Wollongong, NSW 2522, Australia.
authors: David
authors: D
authors: Jakabek
authors: Brain & Mental Health Laboratory, Monash Institute of Cognitive and Clinical Neurosciences, School of Psychological Sciences, Monash University, Clayton, VIC, Australia.
authors: Murat
authors: M
authors: Yücel
authors: Brain & Mental Health Laboratory, Monash Institute of Cognitive and Clinical Neurosciences, School of Psychological Sciences, Monash University, Clayton, VIC, Australia.
authors: Valentina
authors: V
authors: Lorenzetti
authors: School of Psychology and Illawarra Health and Medical Research Institute, University of Wollongong, Wollongong, NSW 2522, Australia. nadia@uow.edu.au.
authors: Nadia
authors: N
authors: Solowij
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D016880:Anisotropy; D001921:Brain / Q000000981:diagnostic imaging; D002188:Cannabis; D003337:Corpus Callosum / Q000000981:diagnostic imaging; D038524:Diffusion Magnetic Resonance Imaging; D056324:Diffusion Tensor Imaging; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008385:Marijuana Smoking; D008875:Middle Aged; D066127:White Matter / Q000000981:diagnostic imaging*; D055815:Young Adult
keywords: Brain; Cannabis; Diffusion tensor imaging; Magnetic resonance imaging; Tractography; White matter