Out of all the five human senses, vision and hearing are the most important, as they are crucial to daily life. An impairment of either of these two senses would be blatantly obvious to a person. But what about our sense of touch? It may seem as though it is somewhat insignificant, but there is evidence to suggest that touch, vision, and hearing are all connected by one vital protein: usherin.
Usherin is a protein that encodes the USH2A gene in humans. It is commonly linked to Usher Syndrome, an inherited disease that leads to visual and hearing impairments. Surprisingly, it also leads to the inability to feel vibrations in the fingertips. There are 9 different genes that can carry a mutation that causes this disease, and these genes, along with their mutations and effects, are very well studied. Due to the connection between these senses and this disease, there is a growing theory that the usherin protein aids the human body in sight, hearing, and touch in order to sense and understand the environment.
The protein responsible for vision and hearing is commonly found in nerve cells, but humans have a microscopic, oval-like capsule within the nerve cell located in our fingers, also known as the a meissner corpuscle. Thus, when we touch a surface, there are sensors within the skin that are transformed into an electrical signal and transmitted to the brain through these nerve cells. The same experience happens when we hear: sounds waves cause vibrations that trigger nerve endings in the cochlea, the cavity of the inner ear. Those vibrations are then transformed into electrical signals, which are then transmitted to the brian using the auditory nerve. In humans, both hearing and touch depend on mechanical force translating into electrical signals.
Image from Wikimedia Commons
In order to dive deeper into the molecular connection between these senses and the protein usherin, Doctor Henning Frenzel and Professor Gary Lewin, neuroscientists in Germany, and their team gathered 518 volunteers, some with Usher Syndrome, several who specifically lack touch sensitivity, and some volunteers who do not suffer from the disease, to
perform an experiment. Each volunteer’s sense of pain, sense of temperature fluctuations, and ability to feel vibrations at 10 to 125 hertz was measured throughout the experiment. Then, the results that came from the volunteers who have Usher Syndrome were compared with the results from the healthy volunteers. The only recognizable difference between the results from the two groups was that the volunteers with Usher Syndrome were four times less likely to pick up the vibrations than the volunteers without the condition.
As a result of this experiment, it became apparent that not all people with Usher Syndrome lack touch sensitivity, but those who have a mutation on the USH2A gene will suffer from poor tactile senses. Thus, this research clarifies that there is genetic commonality between the sense of hearing and touch. There is speculation that in the future, there will be more genes found to affect these two senses as well.