IELTS Reading Practice Test 8: Free, with Answers

AFor most of the twentieth century, scientists believed that the adult brain was essentially fixed. The brain was known to develop rapidly in childhood, but once a person reached adulthood, its structure was thought to be settled: brain cells could die but could not be replaced, and the circuits linking them could not be significantly rebuilt. The Spanish scientist Santiago Ramón y Cajal, whose detailed drawings of nerve cells had earned him a Nobel Prize in 1906, expressed this view memorably in 1913, describing the nerve pathways of the adult brain as "fixed, ended, immutable". The idea had practical consequences. Patients who had suffered brain injuries were often told that any abilities they had not recovered within a few months were lost permanently, and rehabilitation was planned accordingly.

BSome of the strongest evidence for this view came from experiments conducted in the 1960s by David Hubel and Torsten Wiesel. They found that if one of a kitten's eyes was kept closed during the first three months of its life, the eye never developed normal connections with the brain, and the animal remained effectively blind in that eye even after it had been reopened. In adult cats, by contrast, keeping an eye closed for as long as a year had no lasting effect. There appeared to be a critical period early in life, during which the brain could be shaped by experience, and after which it could not. The research earned the two men a Nobel Prize in 1981, and it helped to explain why babies born with cataracts, which cloud the lens of the eye, need surgery as early as possible.

CYet the critical period proved to be only part of the story. In the 1980s, the American neuroscientist Michael Merzenich and his colleagues studied the area of the monkey brain that receives signals from the hand, in which each finger is represented by its own small region. When a monkey lost a finger, the corresponding region did not simply fall silent; when the researchers examined it months later, it had been taken over by the neighbouring fingers, whose territory had expanded to fill the space. Such findings suggested that, even in adults, the brain's maps of the body are continually redrawn according to how much each part is used.

DPerhaps the best-known evidence that adult brains can change comes from London's taxi drivers, who must memorise around 25,000 streets and thousands of landmarks to pass a demanding examination known as the Knowledge, a process that usually takes three to four years. In 2000, the neuroscientist Eleanor Maguire reported that the rear part of the hippocampus, a region of the brain involved in remembering places, was larger in licensed taxi drivers than in other people, and that the longer they had been driving, the larger it was. It remained possible, however, that people with a naturally large hippocampus were simply more likely to become taxi drivers. To rule this out, Maguire and her colleague Katherine Woollett followed 79 trainees and 31 people who were not training, and found no differences between them at the start. Three to four years later, an increase had appeared, but only in the 39 trainees who had passed the examination. There was a cost, though: the qualified drivers performed worse than the other groups on a test of memory for complex visual information.

ELearning a physical skill can produce similar effects. In a study published in 2004, researchers in Germany asked a group of young adults to learn to juggle with three balls, a skill that most mastered within three months. Brain scans showed an increase in grey matter in areas that process visual information about movement, compared with a group who had not practised. When the volunteers were scanned again three months after they had stopped juggling, the increase had partly disappeared. Later research found comparable changes in people around the age of sixty, suggesting that the capacity for change may decline with age but does not vanish.

FSuch discoveries have begun to influence the treatment of patients. After a stroke, people often find that one arm is severely weakened, and as they learn to rely on the other arm, the weaker one is used less and less, a pattern that the American psychologist Edward Taub called learned non-use. Taub's response, known as constraint-induced movement therapy, was to stop patients relying on their healthy arm by placing it in a sling for most of the day, typically for two weeks, while they practised everyday tasks with the weaker arm for several hours a day. Many patients regained a substantial amount of movement, sometimes years after their stroke. Taub had developed the approach from earlier research on monkeys, work that had been fiercely criticised by animal rights campaigners in the 1980s.

GNone of this means that the adult brain is as flexible as a child's, and some questions remain unresolved, notably whether adults can produce new nerve cells at all. In 1998, Swedish and American researchers examined the brains of cancer patients who had been given a chemical that marks newly formed cells, and found new neurons in the hippocampus, even in elderly patients. In 2018, however, two studies published within weeks of each other reached opposite conclusions: one found no new neurons in anyone older than thirteen, while the other found them in people in their seventies. Some scientists believe that differences in the way the brain tissue was collected and stored may explain the conflict. What is clear is that most of the changes described here involve existing cells forming new connections, rather than new cells being born.

Few ideas in medicine are as intuitively appealing as early detection. If a disease can be identified before it causes symptoms, the reasoning goes, it can be treated while it is still small and curable, and lives will be saved. This logic seems so self-evident that questioning it can appear almost irresponsible, and health campaigns routinely urge healthy people to be tested for one condition or another. Over the past few decades, however, a growing body of evidence has suggested that the benefits of screening are often smaller, and its harms considerably larger, than most people assume. I am not arguing that screening should be abandoned; some programmes rank among the great achievements of modern medicine. My argument is that each programme should be judged on the evidence, and that those invited to participate deserve a far more honest account of what it can achieve.

The most successful programmes share certain characteristics, as the test for phenylketonuria, or PKU, illustrates. PKU is a rare inherited condition in which the body cannot break down a substance present in many foods; untreated, it causes severe and permanent brain damage. In the early 1960s, the American scientist Robert Guthrie developed a simple and inexpensive test using a few drops of blood taken from a newborn baby's heel, and children identified in this way can be given a special diet from their first weeks of life, enabling them to develop normally. Here, everything works in screening's favour: the condition is serious, and treatment is far more effective when it begins early. In 1968, the World Health Organization published ten principles, formulated by James Wilson and Gunnar Jungner, that describe precisely such conditions, and they are still widely used to determine whether a screening programme is justified.

The difficulty is that many conditions detected by screening are not like PKU. Cancer, in particular, is not a single disease that inevitably progresses from small and harmless to large and deadly. Some cancers grow so slowly, or stop growing altogether, that they would never have caused symptoms during the person's lifetime. Screening detects these cancers as readily as dangerous ones, and since doctors usually cannot distinguish between them, most are treated with surgery, radiation or drugs that carry risks of their own. This phenomenon, known as overdiagnosis, is particularly troubling because it is invisible: no individual can ever know that they have been overdiagnosed. Instead, a person whose harmless cancer was discovered and removed is likely to believe that screening saved their life, and to urge friends and relatives to be tested too. Paradoxically, therefore, the more overdiagnosis a programme produces, the more grateful survivors it creates, and the more popular it becomes.

South Korea provides a striking illustration. In 1999, the country launched a national screening programme for several common cancers. Thyroid cancer was not among them, but many clinics offered an ultrasound scan of the thyroid gland for a small additional fee, and large numbers of people accepted. By 2011, thyroid cancer was being diagnosed fifteen times as frequently as in 1993, and it had become the most commonly diagnosed cancer in the country, yet the number of deaths from the disease hardly changed. Thousands of people, it appears, had been found to have tumours that would never have harmed them. Most had their thyroid gland removed, which means taking hormone tablets for the rest of their lives, and a minority suffered lasting complications from surgery. After a group of Korean doctors publicly warned against routine thyroid screening in 2014, the number of operations fell sharply.

Such programmes remain popular partly because the statistics used to promote them can be misleading. Campaigners often point to rising five-year survival rates, the proportion of patients still alive five years after diagnosis. Imagine, however, a woman whose cancer would be detected through symptoms at the age of 67, and who would die of it at 70. If screening identifies the same cancer at 64 and she still dies at 70, her survival after diagnosis has doubled, even though her life has not been extended by a single day. This effect, known as lead-time bias, means that survival rates almost always improve when screening is introduced, regardless of whether anyone benefits. The only reliable measure is whether fewer people die of the disease, which can be established only in large trials in which participants are randomly chosen either to be screened or not, and such trials have frequently revealed far more modest reductions in deaths than campaigners suggested.

Those invited for screening are rarely told any of this. Research has repeatedly found that people greatly overestimate its benefits, and invitation letters have traditionally emphasised the possibility of finding disease early while saying little about overdiagnosis. Meanwhile, private clinics in several countries now advertise whole-body scans to healthy customers, scans that frequently reveal minor abnormalities which are almost always harmless but must nevertheless be investigated with further tests, some of them carrying genuine risks. In my view, such scans offer customers anxiety rather than reassurance, and health authorities should actively discourage them.

What, then, should be done? Every screening programme should be justified by evidence that it reduces deaths, not merely by the conviction that early detection must be beneficial, and invitations should present both benefits and harms in plain numbers, so that declining is seen as a reasonable choice rather than a reckless one. None of this requires us to abandon early detection; it requires us to accept that, in medicine as elsewhere, knowing more is not always the same as being better off.