New research has revealed that tickling yourself is impossible, even if you're fooled into thinking that someone else is doing the tickling. The surprising result casts considerable doubt on what scientists think they know about the neural mechanisms of tickling.
Top photo by Sham Hardy via Flickr.
The new study – conducted by Jakob Hohwy and George Van Doorn of Monash University in Clayton, Australia – subjected its participants to a "body swap illusion" in order to test the widely held hypothesis that our brains dampen the effects of a tickle that is self-administered. New Scientist's Anil Ananthaswamy explains:
Using their right hands, both the subject and the experimenter held on to opposite ends of a wooden rod, which had a piece of foam attached to each end. The subject and experimenter placed their left palms against the foam at their end. Next, the subject or the experimenter took turns to move the rod with their right hand, causing the piece of foam to tickle both of their left palms.
In situations where the subjects saw the scene from the experimenter's perspective, they experienced a body-swap illusion, which resulted in them feeling like they owned the experimenter's body. The subjects agreed with statements like "I had lost control of my real hand" and "The experimenter's hand began to resemble my own".
If the experimenter tickled the subject while they were under the illusion, the subject could feel the tickle on their palm. But if the subject initiated the action while still under the illusion – attempting to tickle themselves – the subject didn't feel the tickle on their left palm, even though it felt as though the experimenter was moving the rod. In other words, they couldn't tickle themselves, even under the influence of the illusion.