The fNIRS Glossary Project: A Community-Sourced Glossary of Key Terms

A diverse group of 76 functional near-infrared spectroscopy (fNIRS) researchers, representing a wide range of career stages (from PhD students to experts) and disciplines, operating under the belief that a shared understanding of terminology is essential for clear scientific communication and minimizing misconceptions, created a community-sourced glossary of terms related to fNIRS technologies. Named the fNIRS Glossary Project, the project covers experimental design, pre-processing, data analysis, neuroscience, physics, and areas of mathematics which are believed to be crucial in the understanding and successful and reliable usage of fNIRS in research, industrial, and clinical applications, providing users with a consensus-based resource for fNIRS terminology. An article based on their work was published in Neurophotonics (1).

Functional near-infrared spectroscopy (fNIRS) differs from traditional laboratory and process NIR spectroscopy in its primary applications, wavelength range, and sampling methods. Traditional NIR spectroscopy typically measures over the 680–2500 nm spectral range to analyze chemical composition and physical properties of natural and synthetic products in industrial and laboratory settings. Traditional NIR measures sample constituents like moisture, protein, or fat in agricultural or food products or active pharmaceutical ingredients (APIs) and excipient components of pharmaceutical products. In contrast, fNIRS is a non-invasive neuroimaging technique that measures changes in blood oxygenation and hemodynamics in the brain and typically operates in the spectral range of 650–950 nm to target biological tissues to monitor brain activity. It uses special illumination, sensor configurations, and data processing techniques.

Despite efforts in enhancing the reproducibility and promoting the standardization of the body of knowledge concerning fNIRS, that body, in the opinion of the study’s authors, continues to both widen the knowledge gap and steepen the learning curve, which thus increases challenges for new users entering the field. This gap is especially evident because the technique intersects with other complicated specialties that demand a level of competence, if not expertise, from those participating. As an example, as illustrated in the paper, while the word “probe” is a verb in a general context (to investigate something), in a medical imaging environment, it often denotes a physically invasive measurement.In the context of fNIRS, however, the word refers to a light source or light detector and is neither a verb nor invasive. The authors also note instances where many different items are used that have nearly similar meanings; for example, “source” and “light source,” or “emitter” and “transmitter,” which, for these purposes, all refer to a source of light (1). Obstacles such as these motivated those involved to produce a community-sourced glossary of terms, useful nomenclature, and symbols related to fNIRS technologies, covering experimental design, pre-processing, data analysis, neuroscience, physics, and mathematical areas which the authors believe to be valuable in understanding and using fNIRS successfully and reliably in research, industry, and clinical applications. The Project also offers a field in which synonyms commonly used are available (1).

The team that worked on this project believes that their glossary transcends simple reporting and covers each stage of the research process, from experimental design to analysis, and provides users with all essential terms related to technical and experimental aspects of the field, thus offering researchers assistance in better understanding the technology. They envision that their efforts, by clarifying terminologies and aiding new researchers and experts alike in efficiently communicating through a common understanding and usage of terminologies, will lower whatever barriers may be in place between team members, thus assisting in enhancing diversity, equity, and inclusion in the rapidly expanding field of fNIRS researchers specifically, and the scientific community in general (2).

The fNIRS Glossary Project can be accessed at https://openfnirs.org/standards/fnirs-glossary-project/ (3).

Word or phrase Glossary in a dictionary. © sharafmaksumov- stock.adobe.com

References

1. Stute, K.; Gossé, L. K.; Montero-Hernandez, S. et al. The fNIRS Glossary Project: A Consensus-Based Resource for Functional Near-Infrared Spectroscopy Terminology. Neurophotonics 2025, 12 (2), 027801. DOI: 10.1117/1.NPh.12.2.027801

2. Yücel, M. A.; Lühmann, A. V.; Scholkmann, F. et al. Best Practices for fNIRS Publications. Neurophotonics 2021, 8 (1), 012101. DOI: DOI: 10.1117/1.NPh.8.1.012101

3. The fNIRS Glossary Project. https://openfnirs.org/standards/fnirs-glossary-project/ (accessed 2025-04-22).