急件: 字彙與閱讀 3. 英翻中

When doctors examine a ticklish patient,they place the patient’s hands over theirs during the exam to prevent thetickling sensation. Why does thiswork? Because no matterhow ticklish you may be, you can’t tickle yourself. Go ahead. Try it. The reason is that withevery move you make, part of your brain is busy predicting the sensoryconsequences of that movement. Forinstance, as we write, we are unaware of the feel of the chair and the textureof our socks. Yet we’d immediatelynotice a tap on the shoulder. If theonly information your brain received was pure touch sensation, you wouldn’t beable to tell whether someone was punching your shoulder or whether you’d justbumped into a wall. Since you’d want toreact very differently to those two situations, it’s important for your brainto be able to tell them apart.譯: Howdoes your brain accomplish this goal? Tostudy this, scientists in London developed, of all things, a ticklingmachine. When a person presses a button,a robot arm brushes a piece of foam across the person’s own hand. If the robot arm brushes the hand as soon asthe person presses the button, the person feels the sensation, but it doesn’ttickle. However, a delay of one-fifth ofa second is enough to fool the brain into thinking the robot’s touch has beendelivered by someone else-and then it tickles.譯: This means that some brain region must be able to distinguish your owntouch from someone else’s. Theexperimenters found one: the cerebellum,whose name means “little brain.” Thecerebellum is in an ideal location for distinguishing expected from unexpectedsensations. It receivessensory information of nearly every type. In addition, it receives a copy of all the movement commands sent out bythe motor centers of the brain.