On Thursday night, on CBC’s The Nature of Things, Canadians will get to see the things that have led me to claim that we are now experiencing the biggest change in our understanding of the brain in 400 years — the discovery that the brain can actually change itself, its very structure and function, with the use of thought. Viewers will watch a blind man sink a basketball; a woman with half a brain functioning in life; learning disorders, strokes and brain traumas improved and cured; and chronic pain alleviated.
For 400 years we have been using the wrong model for thinking about the brain, thinking of it as a machine. Ever since Galileo explained that the planetary orbits could be understood as inanimate objects moved by the mechanical laws of motion, scientists have believed that for an explanation to be scientific it has to be mechanistic, or machine-like.
“Mechanistic biology” was born when William Harvey brilliantly showed that the heart was a pump with vessels and valves, a kind of machine. René Descartes argued that the brain and nervous system were similar, with currents running up and down the nerves, which were thought to be vessels too. Descartes also divided the brain into distinct parts. In 1861 Paul Broca showed that people process speech with their left frontal lobes. The triumph of 19th- and most of 20th-century neuroscience was to “map” the brain and show which part or location in the brain did what. The name for this view was “localizationism.” Once machines became electric, localizationists began speaking of the brain’s circuits as “hard-wired,” meaning that the relevant circuits were laid down according to a genetic template and that these circuits were formed, and finalized, in childhood.
Thus the brain came to be seen as a complex machine with parts, each performing a single mental function, an idea with us today when we describe the brain as a kind of computer. This doctrine of the unchanging brain meant that many born with mental limitations, learning disabilities or certain psychiatric problems, or those who suffered brain damage or strokes, were seen, almost by definition, as condemned to live with them. Machines do many glorious things, but they don’t grow new parts, or reorganize themselves. This doctrine promoted a neurological nihilism that spread through our culture: At times it meant that human nature, which emerges from the brain, was seen as being equally rigid.
There were problems with hard-core localizationism from the beginning. As early as 1868 Jules Cotard had shown that children with a diseased left frontal lobe could speak quite well without it. This meant that Broca had only shown there was a tendency for speech to localize left, but it didn’t necessarily have to. Challenges to localization have been accelerating since. The winner of the Nobel Prize for 2000, psychiatrist Eric Kandel, showed that learning actually turns on our genes to make new proteins and create new connections in the brain’s circuits. The neuroscientist Michael Merzenich has shown that with repetition these circuits can become better at what they do and fire faster, more efficient signals. These findings have already been used to cure learning disorders and remedy a variety of psychiatric and neurological problems, treat strokes, raise IQs and preserve the ageing brain. We are not, it turns out, merely the galley slaves of our selfish-gene masters because conscious thought gives us a significant degree of control over their expression in our brains (and elsewhere), by moulding our microanatomy.
These findings amount to the discovery that the adult human brain, rather than being fixed or “hard-wired,” can not only change itself but works by changing itself. It is “neuroplastic”: “neuro” for neuron, the nerve cells in the brain, and “plastic” in the sense of adaptable, changeable, malleable. Neuroplasticity is the property of the brain that allows it to change its structure and function in response to what it senses, what it does and even what it thinks and imagines.
During the course of writing my book (and then filming the CBC documentary) The Brain That Changes Itself, I met Michelle Mack, a woman who was born with half a brain — without her left hemisphere. One would have thought she would be mute, on a respirator in intensive care. Yet Michelle speaks normally, holds a job, loves and has a sense of humour because her right hemisphere reorganized itself to take over what the nonexistent left “should” have been doing.
But the brain does not only change in extreme situations like this; that is how it normally works. That is its modus operandi from cradle to grave.
Dr. Stanley Karansky was 90 years old when we spoke. He was a medic at D-Day. He practised medicine until he was 80. When he turned 89, he told me, he began to have trouble remembering names; he couldn’t register their auditory impressions clearly. He had trouble communicating and withdrew socially. He became less alert and had trouble driving. Then he began The Brain Fitness Program, developed by Michael Merzenich, which sharpened his auditory processing. In six weeks, with an hour a day of brain exercise, Stanley’s age-related cognitive decline was reversed. Studies show this program can turn back the memory clock, so that a person retrieves the memory capacity they had 10 years before, and in some cases even 25 years before.
We can even develop new processing functions. Brain exercises, such as those developed by Barbara Arrowsmith Young (who cured herself of multiple learning disorders, and developed a school to cure others), develop and strengthen weak brain sensory processing areas to above normal capacity. Edward Taub has shown that paralysis caused by strokes, cerebral palsy, multiple sclerosis and brain trauma can be significantly improved using a new kind of brain exercise that reorganizes the brain to work around dead tissue. In some cases, disabilities in place for as long as 50 years can be reversed.
The first neuroplastician of his generation, Dr. Paul Bach-y-Rita focused on the plasticity of the senses. He was so far ahead of his time that many disbelieved it when he showed, in Nature, that he was able to teach congenitally blind patients to see, with cameras delivering gentle electrical signals to their tongues. The sensitive tongue surface behaved like a retina and sent data to the brain’s touch system, which, through the formation of new pathways, was able to turn those signals into sight. His subjects were able to learn to sink basketballs in hoops and discern faces, everyday items, perspective and looming objects.
The changing brain is both more resilient and more vulnerable than we had imagined. Just as the senses can develop, so can the pain system, becoming too good for our own good, giving rise to hypersensitivity syndromes and chronic neuropathic pain. Brain scans are now showing that relationships, too, literally mould our brains, for better or for worse.
Neuroplasticity has its limits — the discovery that the mind can alter the brain does not mean every wish will make it so. Thought, argued Freud, arises in the service of two purposes: First, when we wish to do something, we mentally rehearse it in advance; second, when we are blocked from our goal, we often avoid accepting the reality of dissatisfaction by imagining, in an act of wishful thinking, having achieved it. We now know from the work of neurologist Alvaro Pascual-Leone that mental rehearsal changes brain structure, and that novices who use their imaginations to mentally rehearse practising a melody on the piano systematically develop the same brain circuits as novices who physically practice the melody. These remarkable experiments proved imaginary mental rehearsal changes the brain, but the changes were accomplished through systematic mental work which could be exhausting and not through wishful thinking, which is transitory, fanciful and not usually systematic.
Plasticity requires that we re-examine culture, too. Most think the relationship between the brain and culture is a simple one: The human brain produces culture. In fact our culture also moulds our brains. Just as children with learning disorders can develop new processors, different cultures cultivate different kinds of brains, en masse. The Sea Gypsies, a tribe off the coast of Thailand, learn to see clearly underwater, diving 10 metres in their hunt forfood — an example of a whole culture that has developed a super-sense.
As Richard Nisbett shows in The Geography of Thought, when Asians look at still life pictures they see the relationships between the objects very clearly, but the main object less clearly. Westerners see the opposite. These perceptual differences are not based on a difference of opinion about what to focus on, but on involuntary, unconscious brain processing wired into the subjects by their culture, and alterable by emigration. Thus many of the differences between cultures and civilizations need not be seen as based on either genetic (biological) or experiential differences. Cultural experience shapes biology, and no doubt biology shapes cultural experience. These discoveries promise to reshape, in the most profound way, our understanding of cultural acquisition, conflicts, immigration tensions and even the rates at which we, in a globalized world, can expect each other to change.
Norman Doidge is the author of The Brain That Changes Itself (Penguin).