title: The impact of occipital lobe cortical thickness on cognitive task performance: An investigation in Huntington's Disease.
abstract: BACKGROUND
  The occipital lobe is an important visual processing region of the brain. Following consistent findings of early neural changes in the occipital lobe in Huntington's Disease (HD), we examined cortical thickness across four occipital regions in premanifest (preHD) and early HD groups compared with controls. Associations between cortical thickness in gene positive individuals and performance on six cognitive tasks, each with a visual component, were examined. In addition, the association between cortical thickness in gene positive participants and one non-visual motor task was also examined for comparison.
  
  
  METHODS
  Cortical thickness was determined using FreeSurfer on T1-weighted 3T MR datasets from controls (N=97), preHD (N=109) and HD (N=69) from the TRACK-HD study. Regression models were fitted to assess between-group differences in cortical thickness, and relationships between performance on the cognitive tasks, the motor task and occipital thickness were examined in a subset of gene-positive participants (N=141).
  
  
  RESULTS
  Thickness of the occipital cortex in preHD and early HD participants was reduced compared with controls. Regionally-specific associations between reduced cortical thickness and poorer performance were found for five of the six cognitive tasks, with the strongest associations in lateral occipital and lingual regions. No associations were found with the cuneus. The non-visual motor task was not associated with thickness of any region.
  
  
  CONCLUSIONS
  The heterogeneous pattern of associations found in the present study suggests that occipital thickness negatively impacts cognition, but only in regions that are linked to relatively advanced visual processing (e.g., lateral occipital, lingual regions), rather than in basic visual processing regions such as the cuneus. Our results show, for the first time, the functional implications of occipital atrophy highlighted in recent studies in HD.
authors.affiliation: UCL Institute of Neurology, University College London, UK.
authors.forename: Eileanoir B
authors.initials: EB
authors.lastname: Johnson
authors.affiliation: UCL Institute of Neurology, University College London, UK.
authors.forename: Elin M
authors.initials: EM
authors.lastname: Rees
authors.affiliation: School of Psychological Sciences, Monash University, Clayton, Victoria, Australia; School of Psychology, Australian Catholic University, Melbourne, Victoria, Australia.
authors.forename: Izelle
authors.initials: I
authors.lastname: Labuschagne
authors.affiliation: Department of Genetics and Cytogenetics, and INSERMUMR S679, APHP, ICM Institute, Hôpital de la Salpêtrière, Paris, France.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Durr
authors.affiliation: Centre for Molecular Medicine and Therapeutics, Department of Medical Genetics, University of British Columbia, Vancouver, BC, Canada.
authors.forename: Blair R
authors.initials: BR
authors.lastname: Leavitt
authors.affiliation: Department of Neurology, Leiden University Medical Centre, Leiden, The Netherlands.
authors.forename: Raymund A C
authors.initials: RA
authors.lastname: Roos
authors.affiliation: George-Huntington-Institute, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Reilmann
authors.affiliation: Department of Psychiatry, University of Iowa, Iowa City, IA, USA.
authors.forename: Hans
authors.initials: H
authors.lastname: Johnson
authors.affiliation: UCL Institute of Neurology, University College London, UK.
authors.forename: Nicola Z
authors.initials: NZ
authors.lastname: Hobbs
authors.affiliation: Department of Biostatistics, University of Iowa, Iowa City, IA, USA.
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Langbehn
authors.affiliation: School of Psychological Sciences, Monash University, Clayton, Victoria, Australia.
authors.forename: Julie C
authors.initials: JC
authors.lastname: Stout
authors.affiliation: UCL Institute of Neurology, University College London, UK.
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Tabrizi
authors.affiliation: UCL Institute of Neurology, University College London, UK. Electronic address: r.scahill@ucl.ac.uk.
authors.forename: Rachael I
authors.initials: RI
authors.lastname: Scahill
mesh_terms: D000328:Adult; D000368:Aged; D001931:Brain Mapping; D003072:Cognition Disorders / Q000209:etiology*; D005260:Female; D006801:Humans; D006816:Huntington Disease / Q000150:complications* / Q000473:pathology*; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D009778:Occipital Lobe / Q000473:pathology*; D012044:Regression Analysis; D012720:Severity of Illness Index; D055815:Young Adult
keywords: FreeSurfer; Huntington's Disease; MRI; Occipital lobe; Visual cortex