title: Localization of hemodynamic responses to simple visual stimulation: an fNIRS study.
abstract: OBJECTIVE
  The purpose of the study was to use functional near-infrared spectroscopy (fNIRS) to explore the extent of activation in occipito-parietal cortices to high-contrast checkerboard stimuli. The distributions of oxyhemoglobin (HbO), deoxyhemoglobin (Hb), and total hemoglobin (THb) concentrations were used as measures of cortical activation.
  
  
  METHODS
  Data were collected sequentially using the Frequency Domain Multi-Distance oximeter to record absolute chromophore concentration. Responses to three presentation modes (static, pattern reversal, and ON/OFF stimulation) were compared over 15 locations in two participants. The most effective stimulus was used in 10 participants at the most responsive occipito-parietal sites.
  
  
  RESULTS
  Pattern-reversal stimulation evoked the largest increase in HbO, and this increase was greatest at O1 and O2 (5% to the right and left of the midline occipital location Oz) and diminished at recording locations over the posterior parietal regions in the vertical direction. Hb changes were smaller than those observed for HbO. Significantly smaller responses were recorded over the midline (Oz) compared with those at O1 and O2. Changes in hemoglobin concentration reflected the location of activated brain tissue.
  
  
  CONCLUSIONS
  The authors have demonstrated the distribution of the hemodynamic response using absolute values of hemoglobin chromophores in response to simple but strong stimulation using checkerboard presentations.
authors.affiliation: Glasgow Caledonian University, Department of Vision Sciences, Glasgow, United Kingdom. swijea11@gcal.ac.uk
authors.forename: Sobanawartiny
authors.initials: S
authors.lastname: Wijeakumar
authors.forename: Uma
authors.initials: U
authors.lastname: Shahani
authors.forename: William A
authors.initials: WA
authors.lastname: Simpson
authors.forename: Daphne L
authors.initials: DL
authors.lastname: McCulloch
mesh_terms: D000293:Adolescent; D000328:Adult; D005074:Evoked Potentials, Visual / Q000502:physiology; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D010092:Oximetry / Q000379:methods; D010775:Photic Stimulation / Q000379:methods; D019265:Spectroscopy, Near-Infrared / Q000379:methods; D014793:Visual Cortex / Q000502:physiology*; D055815:Young Adult
chemical_list: D006454:Hemoglobins