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\u2019s 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.<\/p>\n
Key FactsThe 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\u2019s 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\u2019s 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.<\/p>\n
Source: NTNU<\/p>\n
The brain perceives low-frequency sounds in a completely different way than other sounds. Maybe that\u2019s why some people react more to them.<\/p>\n
Sound below 16 Hz is what professionals like to call infrasound. This is sound that is often considered impossible to hear. But that\u2019s not the case.<\/p>\n
\u201cHumans can actually perceive infrasound if the sound level is high enough,\u201d says Carlos Jurado, postdoctoral fellow at the Department of Neuromedicine and Movement Science at the\u00a0Norwegian University of Science and Technology\u00a0(NTNU).<\/p>\n
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.<\/p>\n
Didn\u2019t know how we perceive the sound<\/p>\n
Scientists have long been uncertain about how we perceive infrasound. Now Jurado has investigated the case together with Torsten Marquardt from University College London.<\/p>\n
Recently, their results were published in an article in the Nature magazine\u00a0Scientific Reports.<\/p>\n
\u201cOur research suggests that infrasound is registered in the inner ear in a different way than normal sound does,\u201d says Marquardt.<\/p>\n
Inside the inner ear, there are specialized sensory hair cells that are absolutely crucial for the transmission of sound signals to the brain.<\/p>\n
\u201cBut 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,\u201d Jurado explains.<\/p>\n
\u201cThese 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,\u201d says Marquardt.<\/p>\n
More of a feeling than any other sound<\/p>\n
Maybe that\u2019s why extra low-frequency sounds feel different than other sounds do.<\/p>\n
\u201cThis 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,\u201d says Jurado.<\/p>\n
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.<\/p>\n
Key Questions Answered:Q: If infrasound is technically outside our normal hearing range, why does it feel so deeply unsettling?<\/p>\n
A: It feels strange because it isn\u2019t 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\u2019s structural support cells instead. Because these cells aren\u2019t 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.<\/p>\n
Q: Why do some people complain bitterly about the hum of wind turbines or heat pumps while others don\u2019t notice a thing?<\/p>\n
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\u2019s 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\u2019s cells might ignore the vibration entirely.<\/p>\n
Q: What happens to your perception when low-frequency sound pressure rises even a tiny bit?<\/p>\n
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.<\/p>\n
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<\/p>\n
Author:\u00a0Nancy Bazilchuk<\/a>
Source:\u00a0NTNU<\/a>
Contact:\u00a0Nancy Bazilchuk \u2013 NTNU
Image:\u00a0The image is credited to Neuroscience News<\/p>\n