Hard of hearing have a finer sense of touch

Hard of hearing have a finer sense of touch

23.11.2011

In a recent in the trade magazine „Nature Neuroscience“ published study, a research team led by study director Thomas Jentsch found that genetic hearing loss also affects the sense of touch. Responsible for this is a gene that was previously identified only in connection with deafness. It has now been discovered that this gene also affects the hitherto poorly researched sense of touch. According to the study, the sense of touch of people with genetic hearing loss is more sensitive than that of hearing-impaired people.

Genetically induced deafness
The study looked at Spanish and Dutch families with a DFNA2 type of genetic hearing loss. In this form of deafness, the function of some hair cells in the ear is disturbed by mutation.

To hear, the fine hairs in the ear swing in the rhythm of the sound waves. As a result, potassium ions flow into the hair cells and a nerve signal is transmitted to the brain. The potassium ions then flow off again via a channel in the cell membrane. In the hard of hearing, this channel is defective by a mutation. The channel consists of a protein molecule called KCNQ4. Overloading causes the death of the sensory cells.

Now, researchers found that this mutation also affects the sense of touch. Study leader Thomas Jentsch from the Leibniz Institute for Molecular Pharmacology (FMP) reports: „But we found out that KCNQ4 is not only found in the ear, but also in certain sensory cells of the skin.“ Jentsch continues: „That gave us the idea that the mutation could also affect the sense of touch. We were able to demonstrate this in close cooperation with the lab of Gary Lewin, a touch specialist from the MDC.“

How does the sense of touch work??
Without consciously perceiving it, the sense of touch provides us with vital information about our environment at every moment. If we reach for something, we immediately know from the touch whether it is hot, cold, smooth or rough. Our surface perception works through receptors in the skin, which are divided into pain, mechano and thermoreceptors. So we can perceive pain, vibration, touch, temperature and pressure. Since the sense of touch is still largely unexplored, can be speculated about the exact mechanisms only. It is known, however, that sensory cells are present in the skin for the various touch stimuli. Deformation of these cells produces an electrical nerve signal that is transmitted to the brain.

To unravel the link between genetic deafness and the altered sense of touch, the researchers first developed an investigational model using mice that showed the same mutation in the potassium channel as people with this form of deafness. The tactile receptors in the skin do not die through the defective canal as in the ear. However, the mutant mice showed that they reacted to mechanical stimuli with another electrical signal. The tactile receptors were much more sensitive to vibrational stimuli in the low frequency range. The researchers concluded that the potassium channel seems to act as a kind of damper. If the channel is normal, only fast vibrations and higher frequencies are perceived. If the canal is damaged, the skin is more sensitive.

When investigating the families, the researchers came to the same conclusion. The children who had potassium channel mutations were able to experience much slower vibrations than their healthy siblings. Gary Lewin and Thomas Jentsch summarize: „The skin has several different types of mechanoreceptors that respond to different stimuli qualities, especially to different frequency ranges. The interaction of different receptor classes is important for the sense of touch. Although the receptors we study become more sensitive due to the loss of the potassium channel, the disadvantage of the wrong 'mood' may outweigh other frequencies. With KCNQ4 we have for the first time identified a human gene that alters the properties of the sense of touch.“ (Source: (Nature Neuroscience, 2011; DOI: 10.1038 / nn.2985)