title: Distinct contrast response functions in striate and extra-striate regions of visual cortex revealed with magnetoencephalography (MEG).
abstract: OBJECTIVE
  To spatially and temporally characterise the cortical contrast response function to pattern onset stimuli in humans.
  
  
  METHODS
  Magnetoencephalography (MEG) was used to investigate the human cortical contrast response function to pattern onset stimuli with high temporal and spatial resolution. A beamformer source reconstruction approach was used to spatially localise and identify the time courses of activity at various visual cortical loci.
  
  
  RESULTS
  Consistent with the findings of previous studies, MEG beamformer analysis revealed two simultaneous generators of the pattern onset evoked response. These generators arose from anatomically discrete locations in striate and extra-striate visual cortex. Furthermore, these loci demonstrated notably distinct contrast response functions, with striate cortex increasing approximately linearly with contrast, whilst extra-striate visual cortex followed a saturating function.
  
  
  CONCLUSIONS
  The generators that underlie the pattern onset visual evoked response arise from two distinct regions in striate and extra-striate visual cortex.
  
  
  CONCLUSIONS
  The spatially, temporally and functionally distinct mechanisms of contrast processing within the visual cortex may account for the disparate results observed across earlier studies and assist in elucidating causal mechanisms of aberrant contrast processing in neurological disorders.
authors.affiliation: The Wellcome Trust Laboratory for MEG Studies, Neurosciences Research Institute, Aston University, Aston Street, Birmingham B4 7ET, UK. hallsd@aston.ac.uk
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Hall
authors.forename: Ian E
authors.initials: IE
authors.lastname: Holliday
authors.forename: Arjan
authors.initials: A
authors.lastname: Hillebrand
authors.forename: Paul L
authors.initials: PL
authors.lastname: Furlong
authors.forename: Krish D
authors.initials: KD
authors.lastname: Singh
authors.forename: Gareth R
authors.initials: GR
authors.lastname: Barnes
mesh_terms: D000328:Adult; D001931:Brain Mapping; D015350:Contrast Sensitivity / Q000502:physiology*; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D008875:Middle Aged; D010775:Photic Stimulation; D014793:Visual Cortex / Q000502:physiology*; D014794:Visual Fields; D014795:Visual Pathways / Q000502:physiology*