Mapping the sense of what's going on inside

Scientists are learning how the brain knows what's happening throughout the body, and how that process might go awry in some psychiatric disorders

- Carl Zimmer

Last year, Ardem Patapoutian got a tattoo.

An artist drew a tangled ribbon on his right arm, the diagram of a protein called Piezo. Patapoutian, a neuroscientist at Scripps Research in San Diego, discovered Piezo in 2010, and in 2021 he won a Nobel Prize for the work. Three years later, he decided to memorialise the protein in ink.

Piezo, Patapoutian had found, allows nerve endings in the skin to sense pressure, helping to create the sense of touch. “It was surreal to feel the needle as it was etching the Piezo protein that I was using to feel it,” he recalled.

Patapoutian is no longer studying how Piezo informs us about the outside world. Instead, he has turned inward to examine the flow of signals that travel from within the body to the brain. His research is part of a major new effort to map this sixth, internal sense, which is known as interoception.

Scientists are discovering that interoception supplies the brain with a remarkably rich picture of what is happening throughout the body - a picture that is mostly hidden from our consciousness. This inner sense shapes our emotions, our behaviour, our decisions and even the way we feel sick with a cold. And a growing amount of research suggests that many psychiatric conditions, ranging from anxiety disorders to depression, might be caused in part by errors in our perception of our internal environment.

Someday it may become possible to treat those conditions by retuning a person's internal sense. But first, Patapoutian said, scientists need a firm understanding of how interoception works.

“We've taken our body for granted,” he said.

Everyone has a basic awareness of interoception, whether it's a feeling of your heart racing, your bladder filling or butterflies fluttering in your stomach. And neuroscientists have long recognised interoception as one function of the nervous system.