title: Men and women are different: diffusion tensor imaging reveals sexual dimorphism in the microstructure of the thalamus, corpus callosum and cingulum.
abstract: BACKGROUND
  Numerous magnetic resonance imaging (MRI) studies have addressed the question of morphological differences of the brain of men and women, reporting conflicting results regarding brain size and the ratio of gray and white matter. In the present study, we used diffusion tensor imaging (DTI) to delineate sex differences of brain white matter.
  
  
  METHODS
  We investigated brain microstructure in 25 male and 25 female healthy subjects using a 3T MRI scanner. Whole-head DTI scans were analyzed without a-priori hypothesis using Tract-Based Spatial Statistics (TBSS) calculating maps of fractional anisotropy (FA), radial diffusivity (RD, a potential marker of glial alteration and changes in myelination) and axial diffusivity (AD, a potential marker of axonal changes).
  
  
  RESULTS
  DTI revealed regional microstructural differences between the brains of male and female subjects. Those were prominent in the thalamus, corpus callosum and cingulum. Men showed significantly (p<0.0001) higher values of fractional anisotropy and lower radial diffusivity in these areas, suggesting that the observed differences are mainly due to differences in myelination.
  
  
  CONCLUSIONS
  As a novel finding we showed widespread differences in thalamic microstructure that have not been described previously. Additionally, the present study confirmed earlier DTI studies focusing on sexual dimorphism in the corpus callosum and cingulum. All changes appear to be based on differences in myelination. The sex differences in thalamic microstructure call for further studies on the underlying cause and the behavioral correlates of this sexual dimorphism. Future DTI group studies may carefully control for gender to avoid confounding.
authors.affiliation: Philipps-University Marburg, Center of Brain Imaging, Department of Neurology, Marburg, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Menzler
authors.forename: M
authors.initials: M
authors.lastname: Belke
authors.forename: E
authors.initials: E
authors.lastname: Wehrmann
authors.forename: K
authors.initials: K
authors.lastname: Krakow
authors.forename: U
authors.initials: U
authors.lastname: Lengler
authors.forename: A
authors.initials: A
authors.lastname: Jansen
authors.forename: H M
authors.initials: HM
authors.lastname: Hamer
authors.forename: W H
authors.initials: WH
authors.lastname: Oertel
authors.forename: F
authors.initials: F
authors.lastname: Rosenow
authors.forename: S
authors.initials: S
authors.lastname: Knake
mesh_terms: D000328:Adult; D016880:Anisotropy; D003337:Corpus Callosum / Q000166:cytology*; D056324:Diffusion Tensor Imaging; D005260:Female; D006179:Gyrus Cinguli / Q000166:cytology*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D008297:Male; D012727:Sex Characteristics; D013788:Thalamus / Q000166:cytology*