Rene Descartes’ explanation of pain has long been acknowledged in medicine. He proposed that pain is a purely physical phenomenon – that tissue injury makes specific nerves send a signal to the brain, causing the mind to notice pain. The phenomenon, he said, is like pulling on a rope to ring a bell in the brain. It is hard to overstate how deeply fixed this account has become. In medicine, doctors see pain in Descartes’ terms— as a physical process, a sign of tissue injury.
The limitations of this explanation, however, have been apparent for some time, since people with obvious injuries sometimes report feeling no pain at all. Later, researchers proposed that Descartes’ model be replaced with what they called the gate control theory of pain. They argued that before pain signals reach the brain, they must first go through a gating mechanism in the spinal cord(脊髓). In some cases, this imaginary gate could simply stop pain signals from getting to the brain.
Their most amazing suggestion was that what controlled the gate was not just signals from sensory nerves but also emotions and other “output” from the brain. They were saying that pulling on the rope need not make the bell ring. The bell itself—the mind— could stop it. This theory led to a great deal of research into how such factors as mood, gender, and beliefs influence the experience of pain. In a British study, for example, researchers measured pain threshold and tolerance levels in 53 ballet dancers and 53 university students by using a common measurement: after immersing your hand in body-temperature water for two minutes to establish a baseline condition, you put your hand in a bowl of ice water and start a clock running. You mark the time when it begins to hurt: that is your pain threshold. Then you mark the time when it hurts too much to keep your hand in the water: that is your pain tolerance. The test is always stopped at 120 seconds, to prevent injury.
The results were striking. On average female students reported pain at 16 seconds and pulled their hands out of the ice water at 37 seconds. Female dancers were almost three times as long on both counts. Men in both groups had a higher threshold and tolerance for pain, but the difference between male dancers and male nondancers was nearly as large. What explains that difference? Probably it has something to do with the psychology of ballet dancers—a group known for self-discipline, physical fitness, and competitiveness, as well as by a high rate of chronic(慢性) injury. Their driven personalities and competitive culture evidently accustom them to pain. Other studies along these lines have shown that outgoing people have greater pain tolerance and that, with training, one can reduce one’s sensitivity to pain.
There is also striking evidence that very simple kinds of mental suggestion can have powerful effects on pain. In one study of 500 patients undergoing dental procedures, those who were given a placebo(安慰剂) injection and promised that it would relieve their pain had the least discomfort— not only less than the patients who got a placebo and were told nothing but also less than the patients who got actual drug without any promise that it would work.
Today it is abundantly evident that the brain is actively involved in the experience of pain and is no more bell on a string. Today every medical textbook teaches the gate control theory as fact. There’s a problem with it, though. It explains people who have injuries but feel no pain, but it doesn’t explain the reverse, which is far more common— the millions of people who experience chronic pain, such as back pain, with no signs of injury whatsoever. So where does the pain come from? The rope and clapper are gone, but the bell is still ringing.
The primary purpose of the passage is to               .

A．describe how modern research has updated an old explanation

B．support a traditional view with new data

C．promote a particular attitude towards physical experience

D．suggest a creative treatment for a medical condition

Which statement best describes Descartes theory of pain presented in paragraph 1?

A．The brain can shut pain off at will.

B．The brain plays no part in the body’s experience of pain.

C．Pain can be caused in many different ways.

D．Pain is an automatic response to bodily injury.

The author implies that the reason why the gate control was “amazing” was that it        .

A．offered an extremely new and original explanation

B．was just opposite to people’s everyday experiences

C．was grounded in an ridiculous logic

D．was so sensible it should have been proposed centuries before

The author refers to “chronic back pain” as an example of something that is        .

A．costly, because it troubles millions of people

B．puzzling, because it sometimes has no obvious cause

C．disappointing, because it does not improve with treatment

D．worrying, because it lies beyond the reach of medicine

The last sentence of the passage serves mainly to express that         .

A．scientific judgments are difficult to understand

B．theoretical investigations are generally useless

C．researchers still have a long way to go before the puzzle is made clear

D．there is always something puzzling at the heart of science