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Speed dependency of cerebral blood volume changes during visual cognitive activation measured with NIRS

In this study, multichannel near-infrared spectroscopy (NIRS) was used to measure the change in cerebral hemoglobin concentrations during an incomplete-letter recognition task consisting of a fast section and a slow section. In the task, 85% of the black pixels in the letter images were erased. The display period of the erased letters in the fast section and in the slow section were set to 1000 ms and 3000 ms, respectively, during which the subjects were instructed to respond verbally. Fourteen male volunteers participated in the experiment. Activations in the occipital and bilateral frontal areas were simultaneously examined with three 24-channel probes. The results demonstrated that the oxygenated hemoglobin concentration (oxyHb) during the fast section was relatively higher than that during the slow section. Furthermore, the oxy-Hb difference between the two sections in the occipital areas was more significant than that in the bilateral frontal areas, indicating that for the recognition task in this study, speed change affects the activations in the occipital areas more than those in the frontal areas.