Have you ever tried to tickle yourself? Chances are, you were unsuccessful. Dr. Sarah-Jayne Blakemore, a researcher at the University of London, recently investigated this mystery of the human mind. She confirmed that you cannot tickle yourself — unless you trick your brain, which you can do using only a piece of foam and your palm.
Essentially, you cannot tickle yourself because your brain predicts that you will tickle yourself before you actually do it. As you move, your brain makes lightning-fast decisions, predicting where and how your body will make contact with different objects. The cerebellum receives an internal signal from your motor system called an efference copy, which allows it to precisely predict upcoming planned movements. The cerebellum then elicits a lower neural response when you tickle yourself than if a stranger, whose movements are unpredictable to your nervous system, were to tickle you. This lower neural response results in a reduced sensation at the tickling site.
So, to tickle yourself, you have to fool your brain. Blakemore designed a machine to allow subjects to simulate tickling themselves. Each participant pressed a button, prompting a piece of foam to stroke his or her palm with a delay of up to two seconds. The subject’s cerebellum would predict that the ticklish sensation would occur as the button was pressed, but the sensation would actually occur up to two seconds later. The delay made subjects more ticklish, likely because the cerebellum’s predictions no longer matched what the person was actually feeling.
So, even if you cannot tickle yourself normally, try fooling your brain and see what happens!
Cover Image: We laugh when others tickle us, but not when we tickle ourselves. Photo courtesy of PsyBlog.