If someone asked you to quantify (衡量) the time you spend online, how would you answer? If you're like one-fifth of Americans, you'd likely say “almost constantly.” New research shows that 21 percent of Americans report that they're online more or less constantly.

    Andrew Perrin, a research assistant at Pew, did a survey about Internet use. During the survey, adults were asked how much they go online. 13 percent said they don't go online and 13 percent said they go online several times a week or less. Only 10 percent said they go online once a day and much larger quantities said they go online several times a day (42 percent) or “almost constantly” (21 percent).

    Interestingly, there wasn't a gender split (性别分化) when it came to near constant Internet use. Age seems to be the great divider: Only six percent of people over 65 said they were online that much. Those who reported that they were online all the time included 12 percent of 50- to 64-year-olds, 28 percent of 30- to 49-year-olds and 36 percent of 18- to 29-year-olds.

    Don't suppose that teenagers are online more than adults, however. In another survey, Pew found that while they did have a slight edge on adults in general when it came to “almost constant” Internet use, 24 percent said they were online pretty much all the time. They still fell greatly behind the 36 percent of adults between 18 and 29 years of age who were always online.

    Given that the United Nations considers unrestricted (无限制的) Internet access (接入) to be a human right, the number of Americans who report being online “almost constantly” could rise along with availability and affordability. But it remains to be seen whether being online all the time is actually something to long for, or how constant connectivity will affect American culture in the long term.

    Drug companies have spent billions of dollars searching for therapies to reverse or significantly slow Alzheimer's disease, but in vain. Some researchers argue that the best way to make progress is to create better animal models for research, and several teams are now developing mice that more closely imitate how the disease destroys people's brains.

    The US National Institutes of Health (NIH), the UK Dementia Research Institute and Jackson Laboratory (JAX) - one of the world's biggest suppliers of lab mice - are among the groups trying to genetically design more suitable mice. Scientists are also exploring the complex web of mutations(突变) that influences neurological (神经学的) decline in mice and people.

    "We appreciate that the models we had were insufficient. I think it's sort of at a critical moment right now." says Bruce Lamb, a neuro-scientist at Indiana University ~ho directs the NIH-funded programme.

    Alzheimer's is marked by cognitive impairment(认知损伤) and the build-up of amyloid-protein plaques (淀粉样蛋白块) in the brains of people, but the disease does not occur naturally in mice. Scientists get around this by studying mice that have been genetically modified to produce high levels of human amyloid protein. These mice develop plaques in their brains, but they still do not display the memory problems seen in people.

    Many experimental drugs that have successfully removed plaques from mouse brains have not lessened the symptoms of Alzheimer's disease in people. One focused stumble came last month, when three companies reported that their Alzheimer's drugs had failed in large, late-stage clinical trials. Although the drugs successfully blocked the accumulation of amyloid protein in mice, they seemed to worsen cognitive decline and brain shrinkage in people.

    The drive for better mouse models comes as genomics studies are linking the most common form of Alzheimer's to dozens of different genes. This diversity suggests that each case of the disease is caused by a different combination of genetic and environmental factors. "There is no single Alzheimer's disease," says Gareth Howell, a neuro-scientist at Jackson Laboratory (JAX) in Bar Harbor, Maine.

    Howell argues that scientists' reliance on lab mice with only a few genetically engineered mutations might have limited research. His own work suggests that in mice, just as in people, genetic diversity plays a part in determining how Alzheimer's develops.

    Monkeys seem to have a way with numbers.

    A team of researchers trained three Rhesus monkeys to associate 26 clearly different symbols consisting of numbers and selective letters with 0-25 drops of water or juice as a reward. The researchers then tested how the monkeys combined—or added—the symbols to get the reward.

    Here's how Harvard Medical School scientist Margaret Livingstone, who led the team, described the experiment: In their cages the monkeys were provided with touch screens. On one part of the screen, a symbol would appear, and on the other side two symbols inside a circle were shown. For example, the number 7 would flash on one side of the screen and the other end would have 9 and 8. If the monkeys touched the left side of the screen they would be rewarded with seven drops of water or juice; if they went for the circle, they would be rewarded with the sum of the numbers—17 in this example.

    After running hundreds of tests, the researchers noted that the monkeys would go for the higher values more than half the time, indicating that they were performing a calculation, not just memorizing the value of each combination.

    When the team examined the results of the experiment more closely, they noticed that the monkeys tended to underestimate（低估）a sum compared with a single symbol when the two were close in value—sometimes choosing, for example, a 13 over the sum of 8 and 6. The underestimation was systematic: When adding two numbers, the monkeys always paid attention to the larger of the two, and then added only a fraction（小部分）of the smaller number to it.

    "This indicates that there is a certain way quantity is represented in their brains, "Dr. Livingstone says. "But in this experiment what they're doing is paying more attention to the big number than the little one.”

    Janus, the Roman god, has two faces looking in opposite directions. So does artificial intelligence (AI). On one side are the positive changes, enabling people to achieve more, far more quickly, by using technology to improve their existing skills. Look the other way, though, and there are plenty of potential pitfalls.

    Like Janus, technological change may also cause disruption(混乱), but AI is likely to have a bigger impact than anything since the appearance of computers, and its consequences could be far more disruptive.

    In the years ahead, AI will raise three big questions for bosses and governments. One is the effect on jobs. Although CEOs publicly praise the broad benefits AI will bring, their main interest lies in cutting costs. One European bank asked Infosys to find a way of reducing the staff in its operations department from 50,000 to 500. The McKinsey Global Institute estimates that by 2030 up to 375m people, or 14% of the global workforce, could have their jobs replaced by AI.

    A second important question is how to protect privacy as AI spreads. The internet has already made it possible to track people's digital behavior in minute detail. AI will offer even better tools for businesses to monitor consumers and employees, both online and in the physical world. Consumers are sometimes happy to go along with this if it results in personalised service or promotions. But AI is bound to bring invasion of privacy that is seen as unacceptable. For example, law-enforcement officials around the world will use AI to spot criminals, but may also monitor ordinary citizens.

    The third question is about the effect of AI on competition in business. A technology company that achieves a major breakthrough in artificial intelligence could race ahead of rivals, put others out of business and lessen competition. This is unlikely to happen in the near future, but if it did it would be of great concern.

    It is too early to tell whether the positive changes brought by AI will outweigh the risk. But it will put an end to traditional ways of doing things and start a new era for business and for the world at large.

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Growing evidence shows that dancing can boost brain health and help manage neurocognitive (神经认知的) disorders. So what is it about dance that's different from other regular exercises? 

Helena Blumen, a cognitive (认知的) scientist at Albert Einstein College of Medicine, says the complex (复杂的) mental multitasking that dance requires involves various parts of the brain at the same time. Basically, dancing requires more brain power than simpler repetitive (重复的) exercises. 

While scientists are still learning how the mechanisms of dancing work in the brain, a clearer picture is beginning to appear. Researchers at Otto von Guericke University in Magdeburg, Germany, did MRI scans of older adults who had participated in one of two programs over a six -month period. One group practiced dance and the other did a traditional exercise program with cycling and strength training. While both groups improved their level of physical fitness, the dancers grew more white and gray matter in the parts of the brain responsible for cognitive processes. Both white and gray matter typically decline as we get older, making communication in the brain slow. 

Imagine your brain is a city with loads of roads. The researchers assume the changes brought by dancing contribute to brain plasticity, which is like the city's ability to build new roads, repair old ones or even change the direction of traffic based on how often the routes are used and what the city needs. 

In addition to the physical and neurological (神经学的) benefits, dance can also help people accept what their bodies can and can't do. Dawnia Baynes, 44, developed multiple sclerosis (MS) after her body lose all feeling from the chest down. She recently joined an online dance program for people with MS. Not only has it improved her range of motion, it has also helped her overcome her fear of being judged for how she moves. 

"To see other people moving is like I'm moving," she says, "and knowing that I don't have to be professional and super technical in my dancing makes me comfortable with where I am right now."