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? 

    你有沒有想過人為什么會怕癢？根據科學家的觀點，怕癢是一種防御機制，是人類把它培養來對付那些可能接觸我們皮膚的蟲子、蜘蛛或其他生物。怕癢是我們對侵擾者或威脅產生的內在反應，它使觸覺和痛覺結合起來了。

    腦部與怕癢有關的部位是小腦。小腦監控我們的一舉一動，但對其認為不具威脅性的活動，往往會忽視。舉例來說，我們說話時不會察覺聲帶的振動，但是如有人觸摸我們的肩膀時，我們可能會嚇一跳。這種選擇性的知覺或許就是我們無法自已哈癢的原因。

    我們只會在察覺受到侵犯或攻擊時才會覺得癢。如果試著替自己哈癢，腦部會自動預感到這種“攻擊”從而使我們感覺不到驚嚇。奇怪的是，即使有人知道他要被哈癢了，擔心被人觸摸，也會引起同樣“怕癢”的反應。有些人甚至還沒被哈到癢就先笑了。

    英格蘭近期做了一項關于人是否可以替自己哈癢的科學研究。自愿受測者接上腦部掃描儀，并用一塊軟泡沫綿給手掌哈癢。參與者在被哈癢和自行哈癢時，腦部掃描狀況都受到監視。結果發現，在自行哈癢的過程中，小腦會向腦部的另一部位發出警告，使其預先防范，所以癢的感覺就消失了。

    然而，研究人員也發現了可以替自己哈癢的方法。自愿者用遙控器操縱機器人，延遲片刻之后再讓機器人為自己哈癢，自愿者就會覺得好像是別人在給他們哈癢。看來小腦在發出信號忽視即將到來的動作，然后將注意力轉移到其他事物上。盡管只有零點二秒的時間差，腦部就會“忘記”你在替自己哈癢。所以自己給自己哈癢仍有可能，只不過需要依靠遙控器。誰知道接下來科學還會有什么新發現呢？