Functional Near Infrared Spectroscopy (fNIRS) is an optical neuroimaging technique, which provides a continuous, non-invasive measure of regional brain function. fNIRS uses near infrared light which passes through the skull to measure the colour of the blood in the brain. Oxygenated blood appears bright red and is directed to different regions depending on the local brain activity. By using near infrared light to measure the distribution of oxygenated (red) blood we can map brain function. A typical system contains pairs of optical source and detector probes, which are placed on the scalp over regions of interest and are fixed with a lightweight headband that can be adjusting for varying head sizes of infant. Low light levels are used and continuous measurements can be performed with no risk of damage to the tissue. NIRS technology is portable, low cost and requires minimal set up and time and expert training. The technique is completely non invasive and is tolerant of participant motion. For this reason systems have found widespread application amongst researchers interested in infant cognitive function and have been used to study subjects from birth into infancy, childhood and adulthood.

Below is a short film showing how fNIRS has been used to detect early signs of autism in the UK.