Fig. 4.

(a) A set of raw optical spectra obtained using bbNIRS averaged over 7 min. This panel shows the mean and median spectra shaded with standard deviation and outlined by the highest and lowest spectra. (b) 7-min time series of $\mathrm{\Delta }[\mathrm{HbO}]$ from a representative participant after converting time-dependent bbNIRS spectra (see the conversion algorithm in the Supplementary Material). (c) Frequency-decomposed time series of the curve in panel (b); it includes three curves for endogenic, neurogenic, and myogenic ISO bands. (d) Quantified spectral amplitude of $\mathrm{\Delta }[\mathrm{HbO}]$ after multi-taper spectral analysis with the endo-, neuro-, and myogenic frequency bands shaded by blue, green, and red boxes, respectively. Finally, all the curves presented in (a)–(d) were calculated repeatedly for $\mathrm{\Delta }[\mathrm{HbO}]$ and $\mathrm{\Delta }[\mathrm{CCO}]$ on each lateral forehead, facilitating (e) coherence quantification among each pair of them.