Cellphones, tablets, and computers are keeping children and teenagers awake at night-even when they' re not in use, according to new research. A study published on Monday in JAMA Pediatrics says that media devices are causing kids to sleep less and reducing the quality of sleep that they get. This leads to trouble of staying awake the next day.

Researchers analyzed hundreds of studies of children and teens aged 6-19. The scientists found a strong and consistent association between the use of technology at bedtime and poor sleeping. The reason is not just that kids are staying up too late with their devices. Using a computer can overstimulate the mind and emotions, the researchers say. A smartphone or tablet also gives off a light that affects the body's natural timing. These factors contribute to poor quality sleep. And many kids could be at risk. According to the study,72% of all children and 89% of adolescents have at least one device in their sleep environment. Most of these devices are used near bedtime.

"The harmful association between screen-based devices and kids' sleep is a major public health concern," the study concludes. In their conclusion, the researchers urge parents to understand the damaging influence of device use before sleep.

   Storing food is common in members of the crow family. A new study tested the birds outside for this naturally occurring behavior, which may have evolved（进化）specifically because it gives crows a survival advantage. Some crow species are known to naturally use tools to recover food. So the researchers tested whether the birds could store and recover a tool so they could use it to find their food after a gap of 17 hours — something we wouldn’t expect them to do naturally. But they were able to instantly select the tool out of a number of unnecessary items.

In another experiment, the researchers taught crows to select a token（礼品券）from a number of items so that they could then exchange it for food. Again, the birds then showed that they could plan for the future using this new behaviour. This is different from all of the previous studies in future planning, which have focused on naturally occurring behaviour. For example, we know that chimpanzees select, transport and save appropriate tools for future needs.

These studies have shown that animals can plan for the future — but they leave an important question open for debate. Are animals only able to plan to use abilities that have evolved to give them a specific advantage, or can they flexibly and intelligently apply planning behaviour across various actions? Most critics would say the former, as the animals were tested in naturally occurring behaviour.

But the new research provides the first evidence that animal species can plan for the future using behaviour that doesn’t typically occur in nature. This supports the view that at least some recognitive（认知的）abilities in animals don’t evolve just in response to specific problems. Instead, it suggests that animals can apply these behaviour flexibly across problems in a similar way to humans. We need to study how flexible behaviour evolved. Then we might be able to see how crows’ ability to plan for the future fits in with their broader cognitive powers.

   Darek Fidyka, a 38-year-old Bulgarian, had been paralysed（瘫痪的）from the chest down for four years after a knife attack. Scientists from Britain and Poland took cells from his nose, transplanted them into his back and regrew his spinal cord （脊髓）. Now he can walk and even drive a car. The doctors were delighted but said it was the first step in a long journey.

The breakthrough came after 40 years of research by Professor Geoff Raisman, who found that cells had the possibility to repair damage to nasal （鼻子的） nerves, the only part of the nervous system that constantly regrows. “The idea was to take something from an area where the nervous system can repair itself, and put it into an area that doesn't repair itself,” Professor Raisman said.

Polish doctors injected the nasal cells into Mr Fidyka's spinal cord above and below the injury and used some nerves from his ankle to form a bridge across the damaged tissue. The nasal cells appear to have caused the spinal nerves to repair themselves.

Professor Raisman achieved this with rats in the late 1990s, but this is his greatest success. “I think the moment of discovery for me was Christmas in 1997 when I first saw a rat that couldn't control its hand put its hand out to me. That was an exciting moment, because I realized then that my belief that the nervous system could be repaired was true. ”

Doctors chose the easiest case for their first attempt — it might not work for others. But there is a real sense of hope that an idea once thought impossible has been realized.

David Nicholls, who helped provide money for the breakthrough, said information about the breakthrough would be made available to researchers across the globe.

“What you’ve got to understand is that for three million paralysed people in the world today, the world looks like a totally brighter place than it did yesterday,” he said.