Dysfunction of vestibular system is known factor contributing to dizziness, a common clinical complaint that negatively affects postural stability, spatial orientation and quality of life [1], [2]. Although the peripheral vestibular dysfunction is relatively well understood, the central mechanisms involved in dizziness remain incompletely understood [3]. This gap in understanding is partly due to the limitations of conventional clinical assessments, which often do not sufficiently reflect the underlying neurophysiological processes, particularly involved in complex balance tasks requiring multisensory integration [4].

Moreover, the severity of dizziness varies across individuals and may differentially influence cortical activation and postural control strategies [5], [6]. However, the extent to which dizziness severity modulates these neural mechanisms also remains unclear. Given that individuals with more severe dizziness often rely more heavily on visual or somatosensory cues, it may be that such compensatory behaviors are associated with distinct patterns of cortical activity [5], [7], [8], [9]. Therefore, it is critical to investigate these neural responses under ecologically valid conditions that challenge vestibular function [9], [10]. These considerations suggest the necessity for further research into how dizziness severity interacts with cortical dynamics during postural control, particularly under conditions that challenge multisensory integration [10], [11].

Given the limitations of previous assessments in clearly clarifying these cortical mechanisms, neuroimaging methods capable of monitoring real-time brain activity during ecologically valid postural tasks are essential for advancing our understanding. Functional near-infrared spectroscopy (fNIRS) is a non-invasive neuroimaging technique that enables real-time monitoring of cortical hemodynamics during postural tasks [12]. Previous studies have investigated that fNIRS can sensitively detect changes in oxyhemoglobin (HbO2) concentrations associated with balance demands and sensory conflict, particularly in temporoparietal regions such as the supramarginal gyrus (SMG), angular gyrus (AG), superior parietal lobule (SPL), and superior and middle temporal gyri (STG, MTG), which are implicated in vestibular and multisensory processing [13], [14], [15]. They reported that these regions have been linked to spatial orientation, sensorimotor integration, and self-motion perception [13], [14], [15].

Therefore, the present study aimed to examine differences in cortical activation and balance performance between individuals with mild and moderate-to-severe dizziness using fNIRS and center of pressure (COP) metrics during complex postural condition. We hypothesized that individuals with more severe dizziness would exhibit greater cortical activation and larger postural sway compared to those with mild dizziness.