Functional near-infrared spectroscopy and imaging (fNIRS/fNIRI) is a tool that detects neuroactivation by measuring oxygenated and deoxygenated blood flow. This is accomplished through spectroscopically measuring absorbance of the chromophore hemoglobin in blood that flows to neurally activated regions. Figure 1 shows rat brain vasculature that is constantly modifying itself in response to nutrient and oxygen demands, pruning and sprouting new vessel branches within days.