Scientists have found how cells just beneath the skin surface enable us to feel fine details and textures.
The cells and molecules that initiate vision - rod and cone cells and light-sensitive receptors - have been known since the early 20th century, and the senses of smell, taste, and hearing are increasingly understood.
However, almost nothing is known about the cells and molecules responsible for initiating our sense of touch.
The new study by Columbia University Medical Center researchers is the first to use optogenetics - a new method that uses light as a signalling system to turn neurons on and off on demand - on skin cells to determine how they function and communicate.
The team showed that skin cells called Merkel cells can sense touch and that they work virtually hand in glove with the skin's neurons to create what we perceive as fine details and textures.
"These experiments are the first direct proof that Merkel cells can encode touch into neural signals that transmit information to the brain about the objects in the world around us," said Ellen Lumpkin, associate professor of somatosensory biology.
The findings not only describe a key advance in our understanding of touch sensation, but may stimulate research into loss of sensitive-touch perception, researchers said.
Several conditions - including diabetes and some cancer chemotherapy treatments, as well as normal ageing - are known to reduce sensitive touch.
Merkel cells begin to disappear in one's early 20s, at the same time that tactile acuity starts to decline.
"No one has tested whether the loss of Merkel cells causes loss of function with ageing - it could be a coincidence - but it's a question we're interested in pursuing," Lumpkin said.
In the future, these findings could inform the design of new "smart" prosthetics that restore touch sensation to limb amputees, as well as introduce new targets for treating skin diseases such as chronic itch.
The study was published in the journal Nature in conjunction with a second study by the team done in collaboration with the Scripps Research Institute.
The companion study identifies a touch-activated molecule in skin cells, a gene called Piezo2, whose discovery has the potential to significantly advance the field of touch perception.
