Exploration of cerebral activation using hemodynamic modality separation method in high-density multichannel fNIRS.

Hemodynamic modality separation (HMS) is a method for separating the functional near infrared spectroscopy (fNIRS) signal into the cerebral functional and systemic physiological components based on their difference in hemodynamic modalities: 1) Changes in oxyhemoglobin and deoxyhemoglobin (ΔHbO and ΔHbR) in the cerebral capillaries during neural activation negatively correlate with each other; 2) Other physiological hemodynamic changes originating from major vessels cause a positive correlation in ΔHbO and ΔHbR. We applied this simple method to a high-density multichannel (HDM) fNIRS measurement. In the case of functional signal detection in the parietal area of human adults during a single-sided finger-tapping task, conventional fNIRS data showed very unclear signal laterality, while the functional components separated by the HMS method highly localized at the contralateral area of the tapping side. Using the HMS method for HDM NIRS, we successfully explored cerebral activation in the parietal area. This is the first report that HMS method was utilized for the exploratory detection of cerebral activity.