“Beep！” This is one of the most maddening computer games I’ve ever played. I’m tracking a flock of birds， and when I hit the right one， it explodes with a satisfying “phut.” But as I get better at spotting them， the birds scatter1 ever more wildly across the screen， and I hear that unforgiving “beep”： You missed.
　　Frankly， I feel like giving up. But many players don’t dare. For this is HawkEye2， a brain-training programme that claims it can sharpen my brain beyond simply getting faster at mouse-clicking. Trials have found that older people who play enough hours of this particular kind of game have fewer car crashes—and even， apparently， a lower risk of dementia3.
　　Not so long ago， people thought boys were naturally better than girls at science. We may be making a similar mistake when we assume older people can’t learn as well as younger ones. Until recently， we thought that the brain cells we were born with were a lifetime quota4 and that brains became fixed in adulthood. But in the past decade， with the help of MRI scans and experiments on mice and monkeys， neuroscientists have demonstrated comprehensively that the human brain remains plastic throughout life.5

人們曾经认为，大脑在成年之后就会定型，并且随着年龄的衰老而衰退，不可避免地出现记忆力减退、学习能力下降等症状。然而近几年来，神经科学家发现，人类大脑有着终身的“神经可塑性”。如果我们通过适当的方法给大脑以科学的认知刺激，增强其学习能力，就能保持大脑的年轻和健康状态。方法为何？答案在文中揭晓。

　　When I set out to write a book about the burgeoning numbers of older people in the world， and the challenges they bring， I kept coming across data which suggested that we are far too fatalistic about many aspects of longer lives.6 Many of us can now look forward to an extended middle-age lasting well into our seventies， even beyond. The incidence7 of dementia has fallen by around a fifth in the past 20 years， partly because of giving up smoking. It is widely assumed that productivity declines after 50， but the average age of founders of the highest-growth US start-ups8 is now 47.
　　If we are to enjoy this extra time， we need to extend our mental lifespans to match our physical ones. And that means making the most of breakthroughs in neuroscience which show that our brains keep learning and adapting throughout our lives. Brandnew neurons have been found even in the brains of 70-year-olds with terminal cancer.9 People have recovered from strokes， despite permanently damaging whole areas of their brains， because other areas have stepped in， like airline passengers seizing the controls from an unconscious pilot.10 Scientists are finding new ways to help people with psychiatric disorders overcome their conditions， by calming down certain circuits in the brain and rewiring others.11 　　It all started with the humble canary12. Unlike other songbirds， which churn out the same old tunes， canaries are the hit record producers of the avian world，13 creating new melodies every year to attract a mate. On examining their brains， scientists discovered that they generate new brain cells or neurons each spring， almost doubling their brains in size. Later， it was discovered that humans also generate new neurons. We do this in the hippocampus， which lies deep under the cerebral cortex， learning and consolidating new information.14
　　A big question has been how to put the new brain cells we create to lasting good use， by incorporating15 them deep into mental circuits. Experiments with mice suggest three things help： aerobic exercise16， social contact and new challenges. Eighteen-monthold mice， the equivalent of 65-year-old humans， have developed five times the number of new neurons as fellow rodents17 when given wheels to run on， tunnels to explore， and other mice to make friends with. They also learn to navigate mazes more proficiently than those raised in duller conditions.18
　　Human brains benefit from aerobic exercise too. One group of older people who participated in an aerobic fitness programme for three months were found to have significantly increased their brain volume， unlike another group who did stretching and toning19—perhaps because aerobic exercise increases the blood supply and oxygen to the hippocampus. Moreover， exercise is increasingly recognised as protective against dementia.
　　Just as we get physically fitter， and so can endure longer workouts， so the neurons in our brains start to fire faster， and more in sync with20 each other， when we repeatedly focus intensely on learning a new skill. Neurons which “fire together， wire together”： They give out clearer signals. This is important， because clearer signals improve memory.
　　One reason we forget things as we get older， scientists believe， is that our brains are increasingly struggling through “noise”： fuzzy21 signals given out by neurons which are not syncing properly. We process new events more slowly as we get older， which makes it harder to form a clear memory of someone’s name， or who said what at the party.
　　Many scientists are trying to find ways to reduce the “noise”in our brains as we age. One way is challenging ourselves in ways which require our full attention. There has been research into the effects of playing a musical instrument. Musicians who practise regularly and intensively have been found to have more grey matter in part of their frontal lobe， and less age-related degeneration in other parts of the brain，22 than non-musicians.