Finally, we define the coordinates in the MNI space of a given channel as the weighted mean of the MNI coordinates of the voxels (k) within the brain that can be reached by a given channel. Similarly, the weight is the normalized sensitivity:3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$MN{I}_{x,y,z}(ch)=\sum _{k}^{brain}\frac{normSens(ch,k)\times MN{I}_{x,y,z}(k)}{brainSens(ch)}$$\end{document}MNIx,y,z(ch)=∑kbrainnormSens(ch,k)×MNIx,y,z(k)brainSens(ch)According to equation (3), each fNIRS channel can be spatially represented with a set of MNI coordinates (x, y, z) in respect to the normalized sensitivity and brain sensitivity results obtained from the head atlas of interest (Colin27 or SPM12).