Summary: Researchers have demonstrated that the human brain processes low-frequency infrasound using an entirely unique biological mechanism. When acoustic waves drop too low for standard auditory hair cells to register, the energy bypasses them completely, hijacking the inner ear’s structural support cells instead. These support units generate alternative electric fields that fire off unique nerve pathways, explaining why infrasound registers more as a raw physical sensation or internal hum than a standard audible sound.
Key Facts
- The Infrasound Myth Shattered: While textbooks claim humans cannot hear below 20 Hz, Dr. Carlos Jurado notes that our bodies can absolutely perceive infrasound if the ambient sound pressure level is high enough.
- The Normal Hair Cell Bottleneck: Inside our inner ear’s cochlea, specialized inner hair cells act as the frontline translators for standard sound waves. However, when frequencies drop into the deep infrasound zone, the physical fluid vibrations become too weak and slow to trigger these standard sensory cells, rendering them functionally blind to the noise.
- Hijacking the Inner Ear’s Support Cells: The study unmasked an alternative pathway: the structural support cells inside the cochlea, which normally act as background regulators to adjust hearing sensitivity, are flexible enough to absorb this ultra-low frequency energy.
- Generating Alternative Electric Fields: When these backup support cells are hit by infrasound, they flex and generate local electric fields. These fields are strong enough to trick nearby nerve fibers, triggering alternative bio-electric signals that travel straight into the brain.
- The Non-Linear Volume Spike: This unique biological pathway explains a well-known acoustic puzzle: when infrasound levels creep up even slightly, the perceived volume escalates at an incredibly rapid, non-linear rate. Small steps in environmental pressure instantly make the sound feel overwhelmingly louder.
- The Biological Basis for Noise Sensitivity: Because the density and electrical sensitivity of these cochlear support cells vary naturally from person to person, this mechanism provides a clear biological explanation for why certain individuals are deeply bothered by the hum of heat pumps and generators, while others remain entirely unaffected.
Source: NTNU
The brain perceives low-frequency sounds in a completely different way than other sounds. Maybe that’s why some people react more to them.
Sound below 16 Hz is what professionals like to call infrasound. This is sound that is often considered impossible to hear. But that’s not the case.
“Humans can actually perceive infrasound if the sound level is high enough,” says Carlos Jurado, postdoctoral fellow at the Department of Neuromedicine and Movement Science at the Norwegian University of Science and Technology (NTNU).
Some are more sensitive to low-frequency noise. For example, it can come from ventilation systems, heat pumps, wind turbines, industry, transport, generators or transformers. But this is difficult to measure, because the sound is often perceived more as a hum or physical sensation than more high-frequency sound does.
Didn’t know how we perceive the sound
Scientists have long been uncertain about how we perceive infrasound. Now Jurado has investigated the case together with Torsten Marquardt from University College London.
Recently, their results were published in an article in the Nature magazine Scientific Reports.
“Our research suggests that infrasound is registered in the inner ear in a different way than normal sound does,” says Marquardt.
Inside the inner ear, there are specialized sensory hair cells that are absolutely crucial for the transmission of sound signals to the brain.
“But at very low frequencies, the signals to these hair cells become too weak, and other hair cells, which normally contribute to the hearing process, can still pick them up,” Jurado explains.
“These support cells, which normally receive signals from the brain to regulate hearing sensitivity, generate electric fields that are strong enough to trigger nerve signals that are sent to the brain, so that infrasound is perceived,” says Marquardt.
More of a feeling than any other sound
Maybe that’s why extra low-frequency sounds feel different than other sounds do.
“This may explain why infrasound is experienced differently than normal sound. Small increases in sound pressure quickly make the sound much louder. We can now easily explain this phenomenon as a natural consequence of our new findings,” says Jurado.
The findings may also help to understand why some people are bothered by low-frequency noise, while others do not, as the newly discovered mechanism may vary from person to person.
Key Questions Answered:
A: It feels strange because it isn’t taking the front door into your auditory cortex. Standard sounds vibrate specialized hair cells that your brain decodes as distinct notes or words. Infrasound waves are too slow for those cells, so they take a backdoor path by vibrating your inner ear’s structural support cells instead. Because these cells aren’t meant to handle direct hearing data, they create an unusual bio-electric storm that your brain interprets more as a heavy, physical body sensation or an inescapable internal vibration rather than a standard noise.
A: For decades, people who claimed to be sick or bothered by the low-frequency hum of nearby machinery were often told it was all in their heads. This study changes that narrative by revealing a clear biological variable. The inner ear’s support cells are not identical in every human being; their density, layout, and electrical sensitivity vary naturally from person to person. If you happen to have highly sensitive support cells, an industrial generator or neighborhood heat pump will actively trigger nerve signals in your ear, while your neighbor’s cells might ignore the vibration entirely.
A: This is one of the most dangerous aspects of low-frequency noise pollution. In the standard hearing range, if a sound gets a little bit more intense, you perceive a gradual, predictable increase in volume. But because infrasound relies on backup support cells generating their own alternative electric fields, the system behaves in a highly non-linear way. If the environmental sound pressure of an infrasound source creeps up just a fraction, the resulting electric fields spike dramatically, causing the noise to feel intensely louder and more crushing almost instantly.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this auditory neuroscience research news
Author: Nancy Bazilchuk
Source: NTNU
Contact: Nancy Bazilchuk – NTNU
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Infrasound sensation is mediated by intracochlear electrical potentials” by Carlos Jurado & Torsten Marquardt. Scientific Reports
DOI:10.1038/s41598-026-50179-w
Abstract
Infrasound sensation is mediated by intracochlear electrical potentials
Sound below 16 Hz, commonly referred to as infrasound, has no tonality and is often regarded as inaudible despite being clearly perceivable at sufficient intensity. Perception mechanisms have remained elusive.
One factor decreasing hearing sensitivity towards the lowest sound frequencies is the velocity-coupled sound input to inner hair cells (IHCs), which convert cochlear mechanical vibrations into neural signals. We used non-invasive methods in humans to show that in the infrasound range, the velocity of the mechanical stimulus is reduced to such an extent that displacement-coupled outer hair cells (OHCs) start to be involved in the neural excitation, without mechanical activation of IHCs.
A proposed model illustrates how OHC-generated electrical potentials act on the IHC cell membrane and so plausibly cause synaptic release that leads to auditory sensation. This mechanism explains perceptual characteristics specific to infrasound, such as the shallow slope of sensation threshold curves below 16 Hz and the abnormal growth of loudness with only small increases in sound pressure.
This new physiological insight might help to understand globally spread complaints about very low-frequency environmental sounds.
