Humans have always been fascinated by dreams. The vivid dreams people remember and talk ab

out are REM dream—the type that occur almost continuously during periods of rapid eye movement (REM) during sleep. But people also have NREM dreams—dreams that occur during periods without rapid eye movement called NREM sleep—although they are typically less frequent and less memorable than REM dreams. REM dreams have a story like or dream like quality and are more visual, vivid, and emotional than NREM dreams. Interestingly, blind people who lose their sight before age five usually do not have visual dreams, but they have vivid dreams involving the other senses. A popular belief about dreams is that an entire dream takes place in an instant, but in fact, it is not true. Sleep researchers have discovered that it takes about as long to dream a dream as it would to experience the same thing in real life.

Although some people insist that they do not dream at all, researchers say that all people dream unless they consume alcohol or take drugs that suppress REM sleep. Are dreaming and REM sleep essentially one and the same？ Some researchers have questioned an assumption

long held by some sleep experts that dreaming is simply the brain's effort to make sense of the random firing of neurons that occurs during REM sleep. Are the brain mechanisms responsible for REM sleep the same ones that create the rich dream world we experience？ The answer may be no. It is known that dreams do occur outside of REM sleep. Moreover, the REM state can exist without dreams. These two facts suggest that different but complementary brain mechanisms are responsible for REM sleep and the dreaming that normally occurs within it. There is mounting evidence, says British researcher Mark Solms, that dreaming and REM sleep, while normally occurring together, are not one and the same. Rather, the REM state is controlled by neural mechanisms in the brain stem, while areas farther up in the forebrain provide the common pathway that gives us the complex and often vivid mental experiences we call dreams.

Other researchers suggest that REM sleep aids in information processing, helping people sift through daily experience to organize and store in memory information that is relevant to them. Animal studies provide strong evidence for a relationship between REM sleep and learning. Some studies have revealed that animals increase their REM sleep following learning sessions. Other studies have indicated that when animals are deprived of REM sleep after new learning, their performance of the learned task is impaired the following day. But depriving subjects of NREM sleep had no such effect in the studies.

Research has shown that REM sleep serves an information-processing function in humans and is involved in the consolidation of memories after human learning. Researchers found that research participants learning a new perceptual skill showed an improvement in performance, with no additional practice, eight to ten hours later if they had a normal night's sleep or if the researchers disturbed only their NREM sleep. Performance did not improve, however, in those who were deprived of REM sleep.

There is no doubt that REM sleep serves an important function, even if psychologists do not know precisely what that function is. The fact that newborns have such a high percentage of REM sleep has led to the conclusion that REM sleep is necessary for maturation of the brain in infants. Furthermore, when people are deprived of REM sleep as a result of general sleep loss or illness, they will make up for the loss by getting an increased amount of REM sleep after the deprivation. This increase in the percentage of REM sleep to make up for REM deprivation is called a "REM rebound." Because the intensity of REM sleep is increased during a REM rebound, nightmares often occur.

Why does the author state "The answer may be no" in paragraph 2？

A．To introduce a theory that REM sleep and dreams are not necessarily connected.

B．To contrast dreaming before and after REM sleep.

C．To explain why dreaming and REM sleep are essentially the same.

D．To suggest that more dreams occur inside REM sleep than outside it.