fNIRS is of course a completely different modality than fMRI, however while the mechanics may differ there is overlap in the resulting measurements, ultimately cerebral blood flow and metabolic measurements may be obtained, and neuronal activation often assumed. fNIRS is specific to oxygenated and deoxygenated hemoglobin measurement and quantification due to light back reflection, while fMRI aligns the orientation of the hemoglobin depending on the presence of oxygen. fNIRS offers a much better temporal resolution often 100x or more, while spatially fMRI has the upper hand by roughly 10x.