# A narrative review of functional near-infrared spectroscopy (fNIRS) applications in hearing loss, tinnitus and vestibular disorders

## TL;DR

This paper reviews how functional near-infrared spectroscopy (fNIRS) can be used to study brain activity related to hearing loss, tinnitus, and balance disorders, highlighting its potential in clinical settings.

## Contribution

The paper provides a comprehensive narrative review of fNIRS applications in auditory and vestibular research, emphasizing its utility in challenging populations.

## Key findings

- fNIRS can detect cortical activation patterns in hearing loss and tinnitus, including cross-modal plasticity in cochlear implant users.
- fNIRS shows promise in monitoring treatment effects for tinnitus and predicting cochlear implant outcomes.
- fNIRS enables mapping of vestibular-related cortical networks during balance and multisensory integration tasks.

## Abstract

Functional near-infrared spectroscopy (fNIRS) has emerged as a promising neuroimaging modality for investigating cortical activity in auditory and vestibular domains. Its portability, device compatibility, and motion tolerance make it particularly suited for use in populations that are challenging to study with conventional neuroimaging techniques, such as infants and cochlear implant (CI) users. The present study aims to explore the potential and limitations of this neuroimaging technique in the audiological and vestibular fields, offering an integrated perspective across pediatric, adult and elderly populations.

A narrative review of studies using fNIRS in hearing loss, tinnitus, and vestibular disorders was conducted through searches in PubMed and Scopus up to March 2025. Studies were included if they employed fNIRS to investigate cortical responses in individuals with diagnosed hearing loss, chronic tinnitus or to investigate vestibular function.

A total of 60 studies were reviewed: 36 on hearing loss, 11 on tinnitus, and 13 on vestibular disorders. In hearing research, fNIRS successfully identified cortical activation patterns related to auditory perception, speech processing, and cross-modal plasticity in CI users across development, adulthood and aging. The technique showed prognostic potential in predicting CI outcomes and monitoring listening effort and cognitive load. In tinnitus research, fNIRS consistently demonstrate hyper-activation in the auditory cortex and altered functional connectivity with frontal-limbic networks, reflecting sensory, cognitive, and emotional involvement. The technique was sensitive to treatment effects following interventions such as transcranial stimulation, acupuncture, and cochlear implantation. In vestibular research, fNIRS enabled the mapping of cortical networks involved in balance control and multisensory integration during various stimulation paradigms, including caloric testing, motion platforms, and optic flow in virtual environments. Although current applications are mostly exploratory, findings suggest fNIRS can capture vestibular-related cortical activity in real-world conditions.

fNIRS offers a valuable, non-invasive, and ecologically valid method for investigating auditory and vestibular function across the lifespan. In hearing and tinnitus research, it shows strong potential for clinical translation, especially if methodological standardization is achieved. Applications in vestibular research remain preliminary but promising.