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【原文】
Why Can't You Tickle Yourself
Have you ever thought about why people are ticklish? According to scientists, ticklishness is a defense mechanism humans developed against bugs, spiders, and other critters that may be touching our skin. Feeling ticklish is our built-in response to predators or threats, and combines the sensations of touch and pain.
The part of the brain that is associated with tickling is the cerebellum. It monitors our movements, but ignores movements not perceived as a threat. For example, we do not notice our vocal chords moving when we speak, but we may jump if someone touches us on the shoulder. This selective perception is probably the reason why we cannot tickle ourselves.
We only feel ticklish if we detect a sense of invasion or attack. If we try to tickle ourselves, our brains anticipate this "attack" and prevent us from feeling panicked. Strangely enough, even if a person knows that they are about to be tickled, the fear of being touched may cause the same "ticklish" reaction. Some people laugh even before being tickled.
A scientific study was recently done in England to determine whether or not people can tickle themselves. Volunteers were attached to a brain-scanning device and were tickled on their palms with a piece of soft foam . The participants' brain scans were monitored while they were being tickled, and when they tickled themselves. It was found that during self-tickling, the cerebellum alerted another area of the brain about what to expect, so the ticklish feeling was diminished.
Researchers did find a way, however, for people to tickle themselves. When volunteers activated a robot by remote control to tickle them after a short delay, the volunteers felt as if someone else were tickling them. It seems that the cerebellum sends a signal to disregard the forthcoming movement, then moves on to other things. Your brain "forgets" that you are tickling yourself—even with a delay as short as a fifth of a second. So it is possible to tickle yourself—but only by remote control. What will science discover next?
