# Functional Near-Infrared Spectroscopy **Domain:** Neuroimaging / Neural Interfaces **Doc Type:** Scientific Concept Node **Maturity:** Established and Evolving **Related:** [[Non-Invasive BCI]], [[Multimodal Neural Data Fusion]], [[Functional Magnetic Resonance Imaging]] --- ## Definition **Functional near-infrared spectroscopy (fNIRS)** estimates cortical hemodynamic activity by measuring changes in the absorption of near-infrared light associated with oxygenated and deoxygenated hemoglobin. It is more portable than fMRI but has shallower spatial reach and an indirect relationship to neuronal firing. ## Interface relevance fNIRS can support mobile or multimodal BCI experiments, particularly when fused with faster electrical or magnetic measurements. Its optode geometry, wavelength, sampling, motion correction, and physiological confounds must be retained as metadata.