For many years, the consensus was that the human brain couldn’t generate new cells once it reached adulthood. Once you were grown, you entered a state of neural decline. This was a view perhaps most famously expressed by the so-called founder of modern neuroscience, Santiago Ramón y Cajal. After an early interest in plasticity, he became sceptical, writing in 1928, “In adult centres the nerve paths are something fixed, ended, immutable. Everything may die, nothing may be regenerated. It is for the science of the future to change, if possible, this harsh decree.” Cajal’s gloomy prognosis was to rumble through the 20th century.

Although the notion that the adult brain could undergo significant positive changes received sporadic attention, throughout the 20th century, it was generally overlooked, as a young psychologist called Ian Robertson was to discover in 1980. He’d just begun working with people who had had strokes at the Astley Ainslie Hospital in Edinburgh, and found himself puzzled by what he was seeing. “I’d moved into what was a new field for me, neuro-rehabilitation,” he says. At the hospital, he witnessed adults receiving occupational therapy and physiotherapy. Which made him think… if they’d had a stroke, that meant a part of their brain had been destroyed. And if a part of their brain had been destroyed, everyone knew it was gone for ever. So how come these repetitive physical therapies so often helped? It didn’t make sense. “I was trying to get my head around, what was the model?” he says. “What was the theoretical basis for all this activity here?” The people who answered him were, by today’s standards, pessimistic.

“Their whole philosophy was compensatory,” Robertson says. “They thought the external therapies were just preventing further negative things happening.” At one point, still baffled, he asked for a textbook that explained how it all was supposed to work. “There was a chapter on wheelchairs and a chapter on walking sticks,” he says. “But there was nothing, absolutely nothing, on this notion that the therapy might actually be influencing the physical reconnection of the brain. That attitude really went back to Cajal. He really influenced the whole mindset which said that the adult brain is hardwired, all you can do is lose neurons, and that if you have brain damage all you can do is help the surviving parts of the brain work around it.”

But Cajal’s prognosis also contained a challenge. And it wasn’t until the 1960s that the “science of the future” first began to rise to it. Two stubborn pioneers, whose tales are recounted so effectively in Doidge’s bestseller, were Paul Bach-y-Rita and Michael Merzenich. Bach-y-Rita is perhaps best known for his work helping blind people ‘see’ in a new and radically different way. Rather than receiving information about the world from the eyes, he wondered if they could take it in in the form of vibrations on their skin. They’d sit on a chair and lean back on a metal sheet. Pressing up against the back side of that metal sheet were 400 plates that would vibrate in accord with the way an object was moving. As Bach-y-Rita’s devices became more sophisticated (the most recent version sits on the tongue), congenitally blind people began to report having the experience of ‘seeing’ in three dimensions. It wasn’t until the advent of brain-scanning technology that scientists began to see evidence for this incredible hypothesis: that information seemed to be being processed in the visual cortex. Although this hypothesis is yet to be firmly established, it seems as if their brains had rewired themselves in a radical and useful way that had long been thought impossible.

Merzenich, meanwhile, helped to confirm in the late 1960s that the brain contains ‘maps’ of the body and the outside world, and that these maps have the ability to change. Next, he co-developed the cochlear implant, which helped deaf people hear. This relies on the principle of plasticity, as the brain needs to adapt to receive auditory information from the artificial implant instead of the cochlea (which, in the deaf person, isn’t working). In 1996 he helped establish a commercial company that produces educational software products called Fast ForWord for “enhancing the cognitive skills of children using repetitive exercises that rely on plasticity to improve brain function,” according to their website. As Doidge writes, “In some cases, people who have had a lifetime of cognitive difficulties get better after only thirty to sixty hours of treatment.”

Although it took several decades, Merzenich and Bach-y-Rita were to help prove that Cajal and the scientific consensus were wrong. The adult brain was plastic. It could rewire itself, sometimes radically. This came as a surprise to experts like Robertson, now a Director of Trinity College Dublin’s Institute of Neuroscience. “I can look back on giving lectures at Edinburgh University to students where I gave wrong information, based on the dogma which said that, once dead, a brain cell cannot regenerate and plasticity happens in early childhood but not later,” he says.

It wasn’t until the publication of a series of vivid studies involving brain scans that this new truth began to be encoded into the synapses of the masses. In 1995, neuropsychologist Thomas Elbert published his work on string players that showed the ‘maps’ in their brain that represented each finger of the left hand – which they used for fingering – were enlarged compared to those of non-musicians (and compared to their own right hands, not involved in fingering). This demonstrated their brains had rewired themselves as a result of their many, many, many hours of practice. Three years later, a Swedish–American team, led by Peter Eriksson of Sahlgrenska University Hospital, published a study in Nature that showed, for the very first time, that neurogenesis – the creation of new brain cells – was possible in adults. In 2006, a team led by Eleanor Maguire at the Institute of Neurology at University College London found that the city’s taxi drivers have more grey matter in one hippocampal area than bus drivers, due to their incredible spatial knowledge of London’s maze of streets. In 2007, Doidge’s The Brain that Changes Itself was published. In its review of the book, the New York Times proclaimed that “the power of positive thinking has finally gained scientific credibility”. It went on to sell over one million copies in over 100 countries. Suddenly, neuroplasticity was everywhere.