Our hands and fingertips are amazingly sensitive to texture. We can easily distinguish coarse sandpaper from smooth glass, but we also pick up more subtle differences across a wide range of textures, like the slick sheen of silk or the soft give of cotton.
Information about texture is transmitted from sensors in the skin and through the nerves to the somatosensory cortex, the part of the brain responsible for interpreting the sense of touch. New research by neuroscientists at the University of Chicago shows that as neurons in this part of the brain process this information, they each respond differently to various features of a surface, creating a high-dimensional representation of texture in the brain.
“Objects can have textures that we can describe in simple terms like rough or soft or hard. But they can also be velvety or cottony or furry,” said Sliman Bensmaia, associate professor of organismal biology and anatomy at UChicago and senior author of the study, published this week in the Proceedings of the National Academy of Sciences. “The variety of different adjectives you can use to describe texture just highlights that it’s a rich sensory space. So it makes sense that you need to have a rich neural space in the brain to interpret that too.”
Bensmaia is a leading expert on how the brain and nervous system interpret the sense of touch, including texture. In a 2013 study from PNAS, his lab showed how different kinds of nerve fibers respond to different aspects of texture. Some nerves respond mainly to spatial elements of coarse textures, like the raised bumps of a Braille letter that create a pattern when pressed against the skin. Others respond to vibrations created when the skin rubs across fine textures, like fabrics, which account for the vast majority of textures we encounter in the real world.
In that study, Bensmaia and his colleagues used a rotating drum covered with strips of various coarse and fine textures, such as sandpaper, fabrics and plastics. The drum then ran the textures across the fingertips of Rhesus macaque monkeys, whose somatosensory system is similar to humans, while the researchers recorded the responses in the nerve.