title: Increased MRI-based cortical grey/white-matter contrast in sensory and motor regions in schizophrenia and bipolar disorder.
abstract: Schizophrenia and bipolar disorder share genetic risk factors and one possible illness mechanism is abnormal myelination. T1-weighted magnetic resonance imaging (MRI) tissue intensities are sensitive to myelin content. Therefore, the contrast between grey- and white-matter intensities may reflect myelination along the cortical surface.
  
  
  
  MRI images were obtained from patients with schizophrenia (n = 214), bipolar disorder (n = 185), and healthy controls (n = 278) and processed in FreeSurfer. The grey/white-matter contrast was computed at each vertex as the difference between average grey-matter intensity (sampled 0-60% into the cortical ribbon) and average white-matter intensity (sampled 0-1.5 mm into subcortical white matter), normalized by their average. Group differences were tested using linear models covarying for age and sex.
  
  
  
  Patients with schizophrenia had increased contrast compared to controls bilaterally in the post- and precentral gyri, the transverse temporal gyri and posterior insulae, and in parieto-occipital regions. In bipolar disorder, increased contrast was primarily localized in the left precentral gyrus. There were no significant differences between schizophrenia and bipolar disorder. Findings of increased contrast remained after adjusting for cortical area, thickness, and gyrification. We found no association with antipsychotic medication dose.
  
  
  
  Increased contrast was found in highly myelinated low-level sensory and motor regions in schizophrenia, and to a lesser extent in bipolar disorder. We propose that these findings indicate reduced intracortical myelin. In accordance with the corollary discharge hypothesis, this could cause disinhibition of sensory input, resulting in distorted perceptual processing leading to the characteristic positive symptoms of schizophrenia.
authors.affiliation: Department of Psychiatric Research,Diakonhjemmet Hospital,Oslo,Norway.
authors.forename: K N
authors.initials: KN
authors.lastname: Jørgensen
authors.affiliation: Department of Psychiatric Research,Diakonhjemmet Hospital,Oslo,Norway.
authors.forename: S
authors.initials: S
authors.lastname: Nerland
authors.affiliation: Department of Psychiatric Research,Diakonhjemmet Hospital,Oslo,Norway.
authors.forename: L B
authors.initials: LB
authors.lastname: Norbom
authors.affiliation: NORMENT and K. G. Jebsen Center for Psychosis Research, Institute of Clinical Medicine, University of Oslo,Norway.
authors.forename: N T
authors.initials: NT
authors.lastname: Doan
authors.affiliation: Norwegian Institute of Public Health,Oslo,Norway.
authors.forename: R
authors.initials: R
authors.lastname: Nesvåg
authors.affiliation: Department of Psychiatric Research,Diakonhjemmet Hospital,Oslo,Norway.
authors.forename: L
authors.initials: L
authors.lastname: Mørch-Johnsen
authors.affiliation: Department of Psychiatric Research,Diakonhjemmet Hospital,Oslo,Norway.
authors.forename: U K
authors.initials: UK
authors.lastname: Haukvik
authors.affiliation: NORMENT and K. G. Jebsen Center for Psychosis Research, Institute of Clinical Medicine, University of Oslo,Norway.
authors.forename: I
authors.initials: I
authors.lastname: Melle
authors.affiliation: NORMENT and K. G. Jebsen Center for Psychosis Research, Institute of Clinical Medicine, University of Oslo,Norway.
authors.forename: O A
authors.initials: OA
authors.lastname: Andreassen
authors.affiliation: NORMENT and K. G. Jebsen Center for Psychosis Research, Institute of Clinical Medicine, University of Oslo,Norway.
authors.forename: L T
authors.initials: LT
authors.lastname: Westlye
authors.affiliation: Department of Psychiatric Research,Diakonhjemmet Hospital,Oslo,Norway.
authors.forename: I
authors.initials: I
authors.lastname: Agartz
mesh_terms: D000328:Adult; D001714:Bipolar Disorder / Q000000981:diagnostic imaging*; D002540:Cerebral Cortex / Q000000981:diagnostic imaging*; D005260:Female; D066128:Gray Matter / Q000000981:diagnostic imaging*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D012559:Schizophrenia / Q000000981:diagnostic imaging*; D066127:White Matter / Q000000981:diagnostic imaging*
keywords: Bipolar disorder; cerebral cortex; myelin; schizophrenia; tissue contrast