NIRS Data Analysis for Hemodynamic Responses

Data processing was conducted using Homer 2 software and the MATLAB 2013a platform (The MathWorks Inc., Natick, MA, USA). First, the original raw optical data were converted to the relative concentration changes of HbO, HbR, and HbT hemoglobin based on the modified Beer–Lambert law (MBLL) (22 (link), 23 (link)). The differential pathlength factors (DPF) were 6.51 and 5.86 for 690 and 830 nm, respectively (24 (link)). Then, the data were bandpass filtered between 0.01 and 0.1 Hz to remove task-unrelated noise. Next, the data were segmented into epochs, starting 10 s before the activation onset and ending 20 s after the activation, and epochs with apparent artifacts (such as noise resulting from head motion) were rejected. After removing the noise, the block-averaged hemodynamic responses were calculated.