How Infrasound May Trigger Hearing Sensations

Infrasound, the low-frequency sound below 20 Hz that is often considered inaudible, is actually perceived through electrical potentials generated within the cochlea itself. This is the conclusion of a 2026 study published in *Scientific Reports* by researchers Carlos Jurado and Torsten Marquardt, which clarifies a long-standing mystery in hearing science.

The Methodology: Isolating the Infrasound Signal

Jurado and Marquardt designed experiments to isolate how the inner ear detects very low-frequency sounds. They needed to separate the potential mechanisms: the standard traveling wave in the cochlear fluid that stimulates hair cells for audible sound, versus a more direct electrical or pressure effect.

Their work involved both computational modelling and physiological measurements. They used a well-established model of the human cochlea to simulate responses to infrasound. Critically, they compared these model predictions with actual human perceptual data on infrasound thresholds—the quietest level a person can detect. The goal was to see which physiological signal within the model correlated perfectly with the real-world human ability to sense these low frequencies. The match pointed decisively to an electrical origin.

The Core Finding: Cochlear Electricity, Not Hair Cell Bending

The study found that the perception of infrasound is not primarily driven by the bending of hair cell bundles, which is the essential first step for hearing sounds within the normal audible range. Instead, sensation is mediated by the cochlear microphonic (CM).

The cochlear microphonic is an alternating electrical potential generated directly by the outer hair cells in response to sound stimulation. For mid and high frequencies, this CM is a byproduct of the main hearing process. For infrasound, however, the research indicates it becomes the primary signal. The extremely slow pressure changes of infrasound generate a large-scale, synchronous electrical field across the cochlea. This field is picked up by the auditory nerve as a slow, modulating signal, which the brain interprets as a sensation of pressure, vibration, or deep sound. This explains why infrasound often feels different from a typical auditory experience.

Implications for Hearing Disorders and Sound Sensitivity

This discovery has direct relevance for understanding conditions like tinnitus, hyperacusis, and misophonia. It provides a clear physiological mechanism for why exposure to low-frequency noise, even if not consciously “heard” as a tone, can be distressing or can exacerbate symptoms.

For individuals with hyperacusis, an increased sensitivity to sound, the knowledge that infrasound is transduced via a pervasive electrical field suggests that their discomfort from environments with strong low-frequency rumble (like HVAC systems or traffic) may have a concrete biological basis in cochlear physiology. Similarly, this mechanism could explain some forms of tinnitus that are linked to cochlear stress or dysfunction, particularly those perceived as a pressure or deep roar rather than a pure tone.

The distinction in biological pathways is also instructive. Since infrasound uses a different pathway (direct electrical potentials) than mid-frequency sound (mechanical hair cell stimulation), it helps explain why some therapeutic approaches might work for one type of sound sensitivity but not another. It reinforces the concept that conditions like misophonia and hyperacusis involve distinct neural processes, starting right at the level of the inner ear.

Practical Applications and Future Directions

From a practical standpoint, this research informs better measurement and protection. Audiometric testing currently focuses on frequencies from 125 Hz or 250 Hz upward. The findings argue for more clinical consideration of the very low-frequency spectrum, especially when patients report symptoms triggered by specific environments. It validates patient experiences that were previously difficult to quantify.

In noise control and audiology, it clarifies why traditional hearing protection, which is often less effective at very low frequencies, might still leave an individual exposed to a physiologically potent stimulus. The sensation is happening via a pathway that standard earplugs do not fully block.

Future research can build on this foundation. Studies could investigate whether abnormalities in the cochlear microphonic are linked to specific subtypes of sound tolerance disorders. It also opens questions about how the brain processes this slow, electrical signal from the cochlea. Does it get routed through different neural networks? Understanding this could connect peripheral physiology to central conditions, much like research exploring the cerebellum’s role in hearing disorders connects motor and sensory processing.

The work by Jurado and Marquardt, detailed in their paper (PMID: 42031970 / DOI: 10.1038/s41598-026-50179-w), moves infrasound from a poorly understood phenomenon to a clearly defined sensory process. By identifying the cochlear microphonic as the key mediator, they provide a missing piece in the hearing sciences puzzle. This evidence shifts how clinicians and researchers can think about very low-frequency sound, offering a biological explanation for its unique perceptual effects and its potential role in hearing health disorders.