Scientists built a tickle robot to solve one of biology's strangest mysteries

"In the Touch & Tickle Lab, we invite participants to experience Hektor, the tickle robot, in the name of scientific progress. In a typical visit, participants remove their shoes and socks and then sit in what looks like a dentist's chair. My colleagues and I position their feet on a platform, under which lies Hektor, a robot composed of three electric motors. During a tickle session, Hektor slides probes along the soles of the participants' feet, and they report back on just how much each stroke tickled on a scale of one to 10."

"Throughout this process, we track people's facial expressions, heart rate, muscle activity, breathing and skin conductance (which tells us if they are sweating). Electrodes placed on participants' scalps reveal their brain activity."

"Socrates described the feeling as a mix of pain and pleasure. Aristotle thought ticklishness was a consequence of humans' delicate skin. And Charles Darwin wrote extensively on the subject, hypothesizing that we may be most ticklish in spots that are not frequently touched and only in certain psychological contexts."

Researchers in the Touch & Tickle Lab investigate ticklishness using Hektor, a robot with three electric motors that applies controlled strokes to participants' feet while measuring comprehensive physiological responses including brain activity, heart rate, muscle activity, breathing, skin conductance, and facial expressions. Ticklishness has intrigued philosophers and scientists throughout history—Socrates viewed it as pain mixed with pleasure, Aristotle attributed it to delicate human skin, and Darwin theorized that ticklishness occurs in infrequently touched areas under specific psychological conditions. Contemporary neuroscientists continue exploring fundamental questions about tickling's biological function, evolutionary origins, and the underlying nervous system mechanisms that produce this distinctive sensation.

Read at www.scientificamerican.com