Localization of Hemodynamic Responses to Simple Visual Stimulation: An fNIRS Study

Purpose.: 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