Effects of Frequency-Labeled Narrowband Noise on Postural Stability and Cortical Activation: An fNIRS Study

Background: Maintaining postural stability requires the integration of multisensory information, including visual, vestibular, and somatosensory inputs. This study aimed to investigate the effects of narrowband noise across different frequency bands on static postural balance and cortical activation in healthy adults. Methods: Twenty healthy adults participated in a repeated-measures experiment in which they maintained a tandem stance with eyes closed under four conditions: no sound, low-frequency narrowband noise (500 Hz), mid-frequency narrowband noise (2000 Hz), and high-frequency narrowband noise (5000 Hz). Static balance was assessed using center of pressure parameters, including sway length, ellipse surface, delta X, and delta Y, recorded via a pressure measurement platform. Cortical activation in the premotor cortex (PMC), frontal eye fields (FEF), superior temporal gyrus (STG), and middle temporal gyrus (MTG) was measured simultaneously using functional near-infrared spectroscopy. Results: Mid-frequency narrowband noise significantly improved postural stability, as evidenced by reductions in sway length, ellipse surface, and delta Y compared to the high-frequency and no-sound conditions (p < 0.05). In contrast, high-frequency narrowband noise consistently produced the greatest postural instability, with significantly larger ellipse surface and delta Y values (p < 0.05). Regarding cortical activation, high-frequency stimulation induced significantly greater bilateral activation in the PMC compared to low-frequency stimulation, while all auditory conditions elicited widespread activation across PMC, STG, and MTG. Conclusions: These findings suggest that the frequency characteristics of auditory stimulation exert differential neurophysiological effects on balance control. Mid-frequency narrowband noise may enhance static balance by facilitating sensorimotor integration, whereas high-frequency narrowband noise may induce PMC hyperactivation, potentially contributing to postural instability.