Researchers shed light on hearing loss and touch sensitivity connection
A European team of researchers has discovered that people with a specific form of inherited hearing loss are more sensitive to low frequency vibration. Presented in the journal Nature Neuroscience, the findings provide insight on the association between hearing loss and touch sensitivity. Specialised skin cells must be tuned to enable a person to 'feel'.
Led by the Germany-based groups Leibniz-Institut für Molekulare Pharmakologie (FMP) and the Max Delbrück Center for Molecular Medicine (MDC) Berlin-Buch, researchers assessed people with hereditary DFNA2 hearing loss to get a better perspective on their sense of touch, and not on their ability to hear.
A mutation affecting the function of many hair cells in the inner ear is responsible for this hearing impairment. According to the researchers, this mutation may also have an effect on the sense of touch. The hairs in our inner ear vibrate to the pressure of the sound waves, and these vibrations trigger an influx of positively charged potassium ions into the hair cells. This electric current generates a nerve signal that goes to the brain. The result? Hearing. The potassium ions flow through a channel in the cell membrane and then exit from the hair cells. The mutation damages this potassium channel, what experts call the KCNQ4 protein molecule, in people with hearing impairment. The excess pressure leads to the demise of sensory cells.
'But we have found that KCNQ4 is present not only in the ear, but also in some sensory cells of the skin,' FMP Professor Thomas Jentsch said. 'This gave us the idea that the mutation might also affect the sense of touch. And this is exactly what we were able to show in our research, which we conducted in a close collaboration with the lab of Gary Lewin, a colleague from the MDC who is specialised in touch sensation.'
People can discern differences between surfaces because of the vibrations that occur in the skin when the surface is stroked. This information helps us understand our surroundings.
The team, which included experts from Spain and the Netherlands, said the patients could perceive very slow vibrations that the healthy control group could not perceive. There was a change in the mechanoreceptors for normal touch sensation because of the mutations in the KCNQ4 channel gene.
Professor Jentsch and his colleague, Professor Gary Lewin of the MDC, said DFNA2 patients are extremely sensitive to vibrations: 'The skin has several different types of mechanoreceptors, which respond to different qualities of stimuli, especially to different frequency ranges. The interaction of different receptor classes is important for the touch sensation. Although the receptors we studied became more sensitive due to the loss of the potassium channel, this may be outweighed by the disadvantage of the wrong tuning to other frequencies. With KCNQ4 we have for the first time identified a human gene that changes the traits of the touch sensation.'