困的时候不妨保持饥饿

　　Pulling a late-nighter? You might not want to reach for the sugary snacks to keep you awake. A new study involving fruit flies suggests the sleep-deprived mind is kept alert by hunger。

　　The study examined the effects of starvation on fruit flies that had been genetically engineered to be sensitive to sleep deprivation. Sleepy flies deprived of food stayed awake longer than sleepy flies that got meals. The starving flies also lived longer。

　　"From an evolutionary perspective, this makes sense," said study co-author Matt Thimgan, a Washington University postdoctoral researcher. "If you're starving, you want to make sure you're on the top of your game cognitively, to improve your chances of finding food rather than becoming food for someone else."

　　To tease out the relationships between sleep, starvation and survival, the researchers deprived fruit flies of both food and sleep. They found that starving fruit flies spent more time awake than satiated flies did. The researchers also tested the flies' saliva for enzymes that signal sleepiness and measured the flies' ability to associate a light with an unpleasant stimulus. Both tests showed that the starving flies were alert, not sleepy。

　　The starving flies also survived up to 28 hours without sleep, three times longer than the flies with access to food. The survivors' ability is probably linked to a gene that helps the fruit-fly brain manage the storage and use of fat molecules, the researchers said。