title: Potential effect of skull thickening on the associations between cognition and brain atrophy in ageing.
abstract: BACKGROUND
  intracranial volume (ICV) is commonly used as a marker of premorbid brain size in neuroimaging studies as it is thought to remain fixed throughout adulthood. However, inner skull table thickening would encroach on ICV and could mask actual brain atrophy.
  
  
  OBJECTIVE
  we investigated the effect that thickening might have on the associations between brain atrophy and cognition.
  
  
  METHODS
  the sample comprised 57 non-demented older adults who underwent structural brain MRI at mean age 72.7 ± 0.7 years and were assessed on cognitive ability at mean age 11 and 73 years. Principal component analysis was used to derive factors of general cognitive ability (g), information processing speed and memory from the recorded cognitive ability data. The total brain tissue volume and ICV with (estimated original ICV) and without (current ICV) adjusting for the effects of inner table skull thickening were measured. General linear modelling was used to test for associations.
  
  
  RESULTS
  all cognitive ability variables were significantly (P < 0.01) associated with percentage total brain volume in ICV measured without adjusting for skull thickening (g: η(2) = 0.177, speed: η(2) = 0.264 and memory: η(2) = 0.132). After accounting for skull thickening, only speed was significantly associated with percentage total brain volume in ICV (η(2) = 0.085, P = 0.034), not g or memory.
  
  
  CONCLUSIONS
  not accounting for skull thickening when computing ICV can distort the association between brain atrophy and cognitive ability in old age. Larger samples are required to determine the true effect.
authors.affiliation: Brain Research Imaging Centre, Brain Research Imaging Centre Neuroimaging Sciences University of Edinburgh, Western General Hospital, University of Edinburgh, Edinburgh, Scotland EH4 2XU, UK Computer Science Department, Faculty of Science PMB 001 LASU Post Office, Lagos State University, Ojo Lagos, Lagos, Lagos PMB 001 LASU, Nigeria.
authors.forename: Benjamin Segun
authors.initials: BS
authors.lastname: Aribisala
authors.affiliation: Brain Research Imaging Centre, University of Edinburgh, Edinburgh, Scotland, UK.
authors.forename: Natalie A
authors.initials: NA
authors.lastname: Royle
authors.affiliation: Brain Research Imaging Centre, University of Edinburgh, Edinburgh, Scotland, UK.
authors.forename: Maria C
authors.initials: MC
authors.lastname: Valdés Hernández
authors.affiliation: Department of Psychology, University of Edinburgh, Edinburgh, Scotland, UK.
authors.forename: Catherine
authors.initials: C
authors.lastname: Murray
authors.affiliation: Department of Psychology, University of Edinburgh, Edinburgh, Scotland, UK.
authors.forename: Lars
authors.initials: L
authors.lastname: Penke
authors.affiliation: School of Life Sciences, Heriot-Watt University, Edinburgh, Scotland, UK Department of Psychology, University of Edinburgh, Edinburgh, Scotland, UK.
authors.forename: Alan
authors.initials: A
authors.lastname: Gow
authors.affiliation: Brain Research Imaging Centre, University of Edinburgh, Edinburgh, Scotland, UK.
authors.forename: Susana Muñoz
authors.initials: SM
authors.lastname: Maniega
authors.affiliation: Geriatric Medicine, University of Edinburgh, Royal Victoria Hospital Craigleith Road, Edinburgh EH4 2DN, UK.
authors.forename: John M
authors.initials: JM
authors.lastname: Starr
authors.affiliation: Brain Research Imaging Centre, University of Edinburgh, Edinburgh, Scotland, UK.
authors.forename: Mark
authors.initials: M
authors.lastname: Bastin
authors.affiliation: Department of Psychology, University of Edinburgh, Edinburgh, Scotland, UK.
authors.forename: Ian
authors.initials: I
authors.lastname: Deary
authors.affiliation: Brain Research Imaging Centre, University of Edinburgh, Edinburgh, Scotland, UK.
authors.forename: Joanna
authors.initials: J
authors.lastname: Wardlaw
mesh_terms: D000367:Age Factors; D000368:Aged; D000375:Aging / Q000473:pathology*; D001284:Atrophy; D001921:Brain / Q000473:pathology*; D002648:Child; D003071:Cognition; D056344:Executive Function; D005260:Female; D006801:Humans; D016014:Linear Models; D008279:Magnetic Resonance Imaging; D008297:Male; D008568:Memory; D009483:Neuropsychological Tests; D009929:Organ Size; D011237:Predictive Value of Tests; D025341:Principal Component Analysis; D012886:Skull / Q000473:pathology*; D013997:Time Factors
keywords: ageing; brain atrophy; cognition; magnetic resonance imaging; older people; skull thickening