fNIRS Data Preprocessing with Homer2

Preprocessing of fNIRS data was performed using Homer2 toolbox in Matlab 2013a (MathWorks Inc.). Noisy channels and unrelated time periods were manually identified and removed prior to converting the data into optical density data. Channels with motion artifacts were identified and corrected (Scholkmann et al., 2010 (link)), and removed by performing cubic spline interpolation. A 3th order Butterworth band-pass filter with cut-off frequencies of 0.01–0.1 Hz was then applied to remove artifacts, including cardiac interference (~1.3 Hz) and respiration (~0.25 Hz) (Pinti et al., 2018 (link)). Finally, the modified Beer–Lambert equation was used to convert the optical density data into HbO and HbR concentrations.