Groundbreaking new study reveals how the inner ear processes speech

A new paper, published in the acknowledged journal Nature Communication, reveals a new mechanism delivering vital information to the brain. Among the authors is Professor Thomas Lunner from Eriksholm Research Centre.


Until now, it has been a mystery, how the brain decodes information to distinguish words.

Now, a new international study reveals a previously undiscovered mechanism in the inner ear, which decodes the envelope of a signal and helps the brain process sound.
The findings are published in the world leading scientific journal Nature Communications. Among the many prominent authors from Sweden, Denmark, the US, the UK, and India is Professor Thomas Lunner who is research area manager of the Cognitive Hearing Science group at Eriksholm Research Centre.

“With these findings, we are now able to better understand a part of the hearing system that was not known before,” explains Thomas Lunner.

Read the paper here: 'A mechanoelectrical mechanism for detection of sound envelopes in the hearing organ'

Mechanism sends information to the brain

To understand speech, vital acoustic details, the so-called envelope of the acoustic stimulus, is used to distinguish words. The envelope is the variations in speech created by the movements of lips and mouth in order to form words. The brain only needs a small amount of information about the envelope, but it has so far been unknown how the auditory system extracts this information.

Exactly this mechanism has been unraveled in the new study. Using recordings from human and animal inner ears, the researchers showed that the dominant mechanism for extracting information about the envelope is distortion introduced by mechanoelectrical transduction channels. This electrical distortion tracks the envelope, excites the auditory nerve, and transmits information about the shape of the envelope to the brain. That makes it possible for the brain to process speech and understand words.

Findings may help development of personalized hearing aids

The discovery is an important addition to our understanding of how the inner ear and our sense of hearing work. It may allow professionals to more precisely individualize hearing loss diagnosis and it could spearhead the development of better personalized hearing aids to support the brain.
“To date, it has only been possible to diagnose the health of outer hair cells, for example in newborn screenings. This research could make the first methods to diagnose the health of inner hair cells possible, which has the potential to improve individualized hearing aid processing to better support brain functions, ultimately reducing the effort placed on the brain to understand sound,” says Thomas Lunner.

The new paper is the result of a study spanning 9 years. The study was a collaboration between no less than 13 prominent physicists and inner ear researchers, from five countries.


(Figure: Scanning electron microscopy of cochelar sensory epithelium in the low-frequency region. Show, amongst other things, where the inner hair cells are placed. Credit: Liu W,  Li H, Edin F, Brännström J, Glueckert R, Schrott-Fischer A, Molnar M, Pacholsky D, Pfaller K, Rask-Andersen H (2017). 'Molecular composition and distribution of gap junctions in the sensory epithelium of the human cochlea—a super-resolution structured illumination microscopy (SR-SIM) study' in Upsala Journal of Medical Sciences May 2017) 

Read more news from Erikshoolm Research Centre here.