title: Less developed corpus callosum in dyslexic subjects--a structural MRI study.
abstract: BACKGROUND
  Based on previous studies and due to the characteristics of dyslexia as an auditory phonological decoding disorder, we predicted that the shape of the posterior corpus callosum (CC) would differ between dyslexic and control subjects.
  
  
  METHODS
  Twenty right-handed boys with developmental dyslexia were selected from a carefully screened general population sample (mean age 11 years) and compared to a matched control group. The CC contour was manually traced on the aligned midsagittal MR slice and total callosal area and its subregions were compared between the groups. A statistical shape analysis and subsequent CC classification was performed using a recently developed shape model method.
  
  
  RESULTS
  The shape analysis revealed shorter CC shape in the dyslexic group, localised in the posterior midbody/isthmus region. This region contains interhemispheric fibers from primary and secondary auditory cortices. A shape length difference larger than a fixed threshold in the posterior midbody region could correctly discriminate between control and dyslexic subject in 78% of the cases, where a dyslexic CC was shorter in this region than a control CC. However, there were no significant group differences with respect to overall CC area or subregions.
  
  
  CONCLUSIONS
  A clear shape difference in the posterior midbody of the CC was found between dyslexic and control subjects. This fits with recent other studies that have reported a strong growth factor in this CC region during the late childhood years, coinciding with literacy acquisition. Our results show that the dyslexic group has not undergone the same growth pattern as the normal reading group.
authors.affiliation: Department of Child and Adolescent Psychiatry, Haukeland University Hospital, Bergen, Norway. kple@haukeland.no
authors.forename: Kerstin
authors.initials: K
authors.lastname: von Plessen
authors.forename: Arvid
authors.initials: A
authors.lastname: Lundervold
authors.forename: Nicolae
authors.initials: N
authors.lastname: Duta
authors.forename: Einar
authors.initials: E
authors.lastname: Heiervang
authors.forename: Frederick
authors.initials: F
authors.lastname: Klauschen
authors.forename: Alf Inge
authors.initials: AI
authors.lastname: Smievoll
authors.forename: Lars
authors.initials: L
authors.lastname: Ersland
authors.forename: Kenneth
authors.initials: K
authors.lastname: Hugdahl
mesh_terms: D061085:Agenesis of Corpus Callosum; D002648:Child; D003337:Corpus Callosum / Q000254:growth & development / Q000473:pathology*; D004410:Dyslexia / Q000503:physiopathology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male