A、Sleep can strengthen memories. B、Sleep can recover memories. C、Sleep can protect memories against interference. D、Sleep can ha

Many students try to study the whole night and do not sleep before an exam. Two separate studies show this may do more harm than good. The studies found that a good night’s sleep may improve memory. The findings of both studies appeared in. the publication Nature.
   Scientists at the University of Chicago did one of them. They trained students to listen to unclear speech produced by a machine. Some students listened to the recording after a night of sleep. Others were tested twelve hours after the training, with no sleep. Guess what? The students who slept understood the recording better.
   Professor Daniel Margoliash says sleep has at least two effects on learning. One is to strengthen memories and protect them against interference. The second is to recover memories that have been lost.
   The other study took place at Harvard Medical School in Massachusetts. Scientists trained one-hundred people to repeat two series of finger movements. The act was similar to playing notes on a piano. People who slept between learning the first series and the second did the best. The study suggested that memories are recorded in three steps. Scientists say the process is similar to the way a computer stems information. In humans, they say, the second step requires sleep.