Near-infrared spectroscopy (NIRS)
Near-infrared spectroscopy (NIRS) is a non-invasive means of measuring brain activity. If you hold a flashlight to the palm of your hand in the dark you can see that its light will travel through several centimeters of tissue. NIRS affords optical brain imaging at centimeter depth by projecting near-infrared wavelength light through the skull and measuring how much has been absorbed by the hemoglobin in your blood. That is, NIRS indirectly measures brain activity by measuring the amount of oxygenated and deoxygenated hemoglobin in a particular region of the brain-this relies on the fact that active areas of the brain require blood to sustain neural activity, which is metabolically taxing. NIRS thus allows researchers to "see" brain activity, which is essential to understanding the function of the human brain. We therefore sometimes refer to this use of NIRS technology as "functional NIRS" or fNIRS. Researchers at the University of Nevada, Reno, are using fNIRS and other neuroimaging technologies-including functional MRI (fMRI) and high-density array EEG to study a variety of human cognitive and perceptual abilities.