title: Hedonic tone is associated with left supero-lateral medial forebrain bundle microstructure.
abstract: BACKGROUND
  The medial forebrain bundle (MFB) is an important pathway of the reward system. Two branches have been described using diffusion magnetic resonance imaging (MRI)-based tractography: the infero-medial MFB (imMFB) and the supero-lateral MFB (slMFB). Previous studies point to white-matter microstructural alterations of the slMFB in major depressive disorder (MDD) during acute episodes. To extend this finding, this study investigates whether white-matter microstructure is also altered in MDD patients that are in remission. Further, we explore associations between diffusion MRI-based metrics of white-matter microstructure of imMFB, slMFB and hedonic tone, the ability to derive pleasure.
  
  
  METHODS
  Eighteen remitted depressed (RD) and 22 never depressed (ND) participants underwent high angular resolution diffusion-weighted imaging (HARDI) scans. To reconstruct the two pathways of the MFB (imMFB and slMFB) we used the damped Richardson-Lucy (dRL) algorithm. Mean fractional anisotropy (FA) was sampled along the tracts.
  
  
  RESULTS
  Mean FA of imMFB, slMFB and a comparison tract (the middle cerebellar peduncle) did not differ between ND and RD participants. Hedonic capacity correlated negatively with mean FA of the left slMFB, explaining 21% of the variance.
  
  
  CONCLUSIONS
  Diffusion MRI-based metrics of white-matter microstructure of the MFB in RD do not differ from ND. Hedonic capacity is associated with altered white-matter microstructure of the slMFB.
authors.affiliation: Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology,Cardiff University,Cardiff,UK.
authors.forename: T
authors.initials: T
authors.lastname: Bracht
authors.affiliation: Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology,Cardiff University,Cardiff,UK.
authors.forename: A N
authors.initials: AN
authors.lastname: Doidge
authors.affiliation: Neuroscience, Mental Health Research Institute,Cardiff University,Cardiff,UK.
authors.forename: P A
authors.initials: PA
authors.lastname: Keedwell
authors.affiliation: Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology,Cardiff University,Cardiff,UK.
authors.forename: D K
authors.initials: DK
authors.lastname: Jones
mesh_terms: D000328:Adult; D059445:Anhedonia / Q000502:physiology*; D003865:Major Depressive Disorder / Q000473:pathology* / Q000503:physiopathology*; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D008474:Medial Forebrain Bundle / Q000473:pathology*; D066127:White Matter / Q000473:pathology*; D055815:Young Adult
keywords: white matter