Back to Basic Series: functional NIRS

Abstract

Functional Near-Infrared Spectroscopy (fNIRS) is a non-invasive brain imaging method that measures hemodynamic responses associated with neural activity. Originating from near-infrared spectroscopy (NIRS), fNIRS utilizes the 700-1000 nm wavelength range to penetrate biological tissue and detect changes in oxygenated and deoxygenated hemoglobin (Hb). This technique is grounded in the modified Beer-Lambert law, which accounts for light scattering in tissue. fNIRS is considered safe for all age groups due to minimal thermal effects and has proven effective in both research and clinical settings. Optical Topography (OT), developed to visualize brain activation in two dimensions, allows for multichannel, real-time mapping of cerebral function. The combination of optical engineering and psychological experimental design is crucial, particularly in isolating cognitive functions using task-control paradigms. An example includes the study of language-related brain activity during word retrieval and writing tasks. Clinically, fNIRS has been approved for use in diagnosing language-dominant hemispheres and epileptic foci and is now applied to the differential diagnosis of depressive symptoms. Recent studies have also explored its potential in personalized medicine, including the assessment of developmental disorders and drug efficacy. Notably, fNIRS has been successfully applied in neonatal research. A landmark study demonstrated that even newborns show significant left-hemisphere activation in response to forward-played native language speech, as opposed to reversed speech or silence. This suggests an innate neural basis for language perception. These findings provide foundational evidence supporting the role of biological predispositions in language acquisition and contribute to the broader understanding of neurodevelopment.