Near Infrared Spectroscopy (NIRS), also called functional Near Infrared Spectroscopy (fNIRS), optical recording technology measures changes in the brain’s oxygen absorption based on optical properties of hemoglobin (blood). fNIRS technology is presently growing in use world-wide to assess cortical activity during cognitive tasks in both typical populations (including adults, children, and infants) as well as in persons with atypical cognitive disorders. fNIRS, however, has been used for decades in the physiological study of, for example, the heart, breast tumors, cerebral blood flow in premature infants, and the like.
Using safe non-ionizing wavelengths of light in the near-infrared range (700-1000nm), fNIRS technology ideally lends itself to studies of higher cognition over other brain imaging technologies because it has both good temporal resolution (~5 seconds) and good spatial resolution (~4 cm depth), without the use of, for example, radiation, and without requiring research participants to be in an enclosed structure. With fNIRS, participants’ cortical activity can be assessed while they are comfortably seated in an ordinary chair (adults and children) or even seated in mom’s lap (infants). Notably, fNIRS is the only portable neuroimaging system (the size of a desktop computer), virtually silent, and can tolerate participants’ subtle movement. This latter feature is particularly outstanding for the neural study of higher cortical functions, such as human language, which necessarily has as one of its key components the movement of the mouth in speech production or the hands in sign language.
The fNIRS system can be used to ask new questions in science never before possible with traditional behavioral and/or brain imaging methods (such as the fMRI, ERP, etc.). For example, Petitto and team have used the fNIRS technology to track very specific swatches of tissue in the infant brain classically associated with language, auditory, and higher cognitive processes over time. Indeed they have tracked such tissue throughout the course of human development (spanning infants, children, and adults) to identify typical brain development and its associated linguistic and cognitive functions, as well as atypical brain-function development. To be sure, the fNIRS system has made it possible to identify infants who are at risk for language disorders even before their expression of language, and well before the age at which diagnoses of language disorders are clinically available (which, for language, normally does not occur until around age 3 and beyond). In turn, such early identification has benefits for the early remediation of children when neural plasticity is most heightened, and, crucially, it makes possible the design of the most appropriate/targeted therapies.
Meeting and Advancing Challenges
Once the data were recorded from infants, children, or adult brains, an early challenge with the fNIRS technology was to render it in a form that was interpretable and comparable relative to other existing brain imaging technology, such as the fMRI. Towards this end, Petitto and colleagues have also advanced fNIRS analysis and brain mapping methods that are now publicly available and widely used (see JoVE article).
For more information: Hitachi Medical Systems