by Norman Doidge
Norman Doidge presents the topic of brain plasticity through the research of dozens of neuroscientists. He interviews many of them as well as some of their patients, and presents the human side of this highly complex subject. Along the way he provides just enough science to convince us that the adult brain is plastic – that yes, an old dog can learn new tricks.
In telling the story, he traces some of the history of brain science, and how for the past few centuries the common belief was that the adult brain was a fixed instrument, similar to a complex machine. In retrospect this seems like an unsurprising outcome from an age in which the rise of industrialism and mechanization came to dominate the world. Theories that fit with the machine age were readily adopted, while theories that opposed it, such as plasticity, were disregarded. In the 1800’s science saw the rise of the localizationists, who believed that each physical area of the brain corresponded to a specific function, such as speech or vision. The most famous of these, Paul Broca, published some research that partially dispelled his own localization theory, yet was ignored. The world wanted to see the brain as a machine.
Doidge tells of the struggle by dozens of researchers to dispel these entrenched beliefs, and of a few human patients who were saved in the process. The results from these efforts are stunning. We are introduced to dozens of people with various debilitating problems, some congenital and some from accidents. By understanding the principles of brain plasticity and by designing exercises or devices to harness that plasticity, many of these patients achieve remarkable reversals of their disabilities.
The author does a masterful job of blending human interest with science, and ultimately of providing an entertaining, educational and uplifting story. What becomes most obvious after reading this book is that the adult brain is fully equipped to continue learning well into old age. That’s the good news. For many, the bad news will be that adult learning takes significant amounts of work – more than most are willing to expend. However, by understanding the principles of plasticity that have emerged from research, the reader can at least attempt to divine the most effective methods of learning, and the most effective methods of unlearning. Sorry, but there is no magic bullet, no smart pill. For adults, learning is hard work.
The story opens with Cherly, a 39 year-old woman who had a hysterectomy five years ago. She was given an excessive dose of the antibiotic gentamicin, despite the fact that such an excess was known to cause dangerous side effects. The side effect for Cheryl was that her vestibular apparatus stopped working. The vestibular apparatus is a set of small, fluid-filled tubes near the inner ear that measure acceleration and the position of our bodies relative to gravity. It is the silent hero of balance, keeping us from falling. Cheryl has lost 99 to 100% of her vestibular function. She cannot stand or walk without falling down. Her doctors told her that she would never recover.
Doidge goes to visit Cheryl and the people that are going to try to fix her. He is in the office of Dr. Paul Bachy-Rita and his team. Cheryl is there and he meets her. She says that for the past five years, she perpetually has the feeling that she is falling. Even when she is laying down she feels this way. She cannot stand or walk without falling. Her life has become and endless nightmare. People with Cheryl’s disability are call wobblers and it is a debilitating problem.
Bachy-rita is a firm believer in the brain’s ability to quickly adapt its processing power as needed and has designed a gadget to replace Cheryl’s vestibular apparatus. He has attached accelerometers in two planes to a construction helmet. A wire leads from the accelerometers to a small device about the size of a piece of gum that Cheryl will hold on her tongue. The device has a few hundred electrodes that will respond to signals from the accelerometer. As she moves or tilts to one side or the other, the electrodes will send small pulses to her tongue that will feel like champagne bubbles. When she leans backwards just a bit, the back of her tongue will feel the pulses, and leaning forward will register toward the front of the tongue. There is no practice session or training. Cheryl puts on the helmet, places the electrode device on her tongue then stands. Much to her surprise and to the delight of the Bachy-rita team, Cheryl instantly learns to read her position from messages sent through her tongue. She does not fall, and after a minute of this remarkable feat, she is brought to tears as five hopeless years yield to her new lease on life. Remarkably, after one minute wearing this contraption, she finds a residual benefit of another 20 seconds of balance after removing the device.
She tries again, and the same pattern emerges. There seems to be a residual benefit to the device of roughly an extra third of the time. Ultimately, through wearing this device, which is eventually made into a much smaller and more elegant design, Cheryl regains her balance, using an external accelerometer sending messages to her tongue. To accomplish this, the brain had to rewire itself to direct sensory input from the tongue to the muscles involved in balance. The author tries the device too. He puts on the helmet, puts the device on his tongue, closes his eyes and finds that he can instantly navigate with this new method of sensory input. The fact that Cheryl and Doidge could do this is a remarkable demonstration of plasticity. That their brains could adapt instantly is, well, amazing. Cheryl has her life back.
Next we are introduced to Barbara Arrowsmith Young. As a child she exhibited areas of brilliance, such as remarkable memory and tremendous motivation. However these qualities coexisted with other areas of retardation. Her left leg was shorter than the right, her left eye less alert, her spine twisted. “She had a confusing assortment of disabilities,” writes Doidge. She had trouble pronouncing words, could not manage spatial reasoning so would lose things constantly. She was hopelessly clumsy.
She had to keep all of her belongings in a pile. She was always getting lost. She had a decreased sense of touch on her left side so was always getting bruised there. Her span of vision was narrow so could see only a few letters at a time which made reading difficult. Perhaps worst of all, the part of her brain responsible for understanding the relationships between symbols did not function properly. So she had trouble understanding grammar, math concepts, logic and cause and effect. She could not distinguish between ‘father’s brother’ and ‘brother’s father.’ She could not read a clock or understand the difference between left and right. She was dyslexic. She could memorize that 5 times 5 is twenty five, but could not understand why.
Barbara managed to get through elementary and high school by using her extraordinary memory. She would memorize pages of facts. If tests were fact-based, she would score 100. If conceptually based, she could count on a dismal failure. She understood nothing in real time, but only after studying the past, replaying movies or songs dozens of times to try to comprehend them. She could not pick up verbal cues in social settings, so was socially awkward.
Growing up in the 1950’s and 1960’s, there was no help available for her. One either conformed or didn’t, either succeeded or didn’t. Teachers said she had a mental block against learning. Relying on her superior memory, Barbara completed high school and attended college in Canada where she studied child development, hoping to sort out her own issues. There, despite her shortcomings, teachers noticed her remarkable ability to pick up non-verbal cues in observing children. She ended up teaching the course and attending graduate school. There she met Joshua Cohen, another student, also learning-disabled, who understood her. He introduced Barbara to the work of Alexandr Luria, who decades earlier had studied soldiers with brain damage from WWII.
Barbara read of one famous patient named Zazetsky, whose list of maladies sounded like a description of her own life. At last she realized that ‘her brain deficit had an address.” It was at this time in her life that a research paper appeared on her desk. Mark Rosenzweig at the University of California at Berkeley, had studied rats in stimulating and non-stimulating environments, and found in post-mortem dissections that the rats in enriched environments had measurable increases in neurotransmitters, brain mass, blood supply, and synaptic connections. He was at the forefront of connecting activity with increased physical manifestation in the brain.
For Barbara, lightening struck – her brain would respond to stimulation. She believed she would need to link Luria’s work with Rozensweig’s, and to design mental exercises to strengthen her weakest areas. So she set to work, with the help of her friend Joshua, learning to read clocks. She would practice hours on end, trying to understand why at 2:45 the hour hand was three-quarters of the way toward three. After several weeks of intense effort and little sleep, she added hands for seconds and even sixtieths of a second. Soon she could read clocks much faster than normal people. But she noticed collateral benefits as well. After the intensive clock study, she found she could grasp grammar, math and logic. Conversations started to make sense in real time.
Spurred on by these successes, she developed exercises for her other deficits such as her lack of spatial reasoning, and brought these skills to normal levels. In 1980 she and Joshua opened the Arrowsmith School in Toronto and continued to develop exercises for others with various brain disabilities. The school has since expanded and has affiliates in many locations: http://www.arrowsmithschool.org.
We are next introduced to Michael Merzenich, who is described as the leading researcher of his time in brain plasticity. Living in Santa Rosa, California, this energetic scientist has made some seemingly bold claims. He believes that brain exercises may be as useful as drugs to treat some severe conditions such as schizophrenia, and that radical plasticity exists even in the elderly. He argues that practicing a new skill under the right conditions can change huge numbers of synapses, thus altering our brain maps.
Merzenich’s claims stem from the work he has done on brain maps. He found that after injuries such as cut nerves, brain maps will change. So if a sensory nerve leading from a finger tip to a specific area of the cerebral cortex is cut, then you no longer have feeling in that finger. The old theory of a fixed brain held that the neurons fed by the cut nerve are now out of a job until the cut nerve is repaired.
Merzenich showed that instead, after prolonged non-use, the brain map from the cut nerve will instead be taken over by adjacent areas of the cortex, just as an abandoned building will taken over by squatters. Nature abhors a vacuum, and so does our neuroplastic brain. Merzenich conducted further research on plasticity and found that even in normal adult monkeys, the location of brain maps could change from day to day. Stimulate a toe on a monkey and a specific area of the cortex would activate. Stimulate the same toe in the same place tomorrow, and a close but slightly different cortical area would light up. Brain maps are continually changing based on demand. So plasticity is competitive, conforming to the principle of ‘use it or lose it.’
This continual competition for cortical real estate explains why it is so difficult for adults to learn a new language. Immersed in their native tongue on a daily basis for decades, their brain map for language is large and entrenched. To begin to overcome that cortical monopoly, adults must often engage in immersion learning, where great efforts are made to learn the new skill, while the old skill is not exercised.
Following the work of Donald Hebb from 1949 (which Freud proposed decades earlier), Merzenich showed the effect of timing on forming new brain maps – i.e., learning. He proved what had been hypothesized by Hebb and described as ’neurons that fire together wire together.’ Through experiments with monkeys, his lab demonstrated that with learning, neurons become faster and send clearer signals. Clearer signal have more impact on the brain, as memory is only as clear as the original signal. Speed is one measure of intelligence, as thinking quickly is an important survival skill. He also discovered that paying close attention is necessary for long-term plastic change. So while some boast of their ability to multi-task, such divided attention slows or prevents long-term learning. Also important to learning is the brain’s reward system. When a reward is perceived, the brain secretes neurotransmitters, such as dopamine and acetycholine, which help consolidate long-term changes to the brain map.
Merzenich and his colleagues formed a company called Scientific Learning and designed a system called Fast ForWord, which claims to improve the language and other capabilities of children with learning disabilities. From my own googling, it appears that the Merzenich is no longer associated with this company, having returned to research. There are also a number of sites claiming that there have not been proper, peer-reviewed control studies to measure the effectiveness of these programs. Doidge tells of a number of students with various learning disabilities, including autism, who had great success with these programs. However after reading online counter-arguments, the jury is still out.
In studying what Doidge refers to as ‘the catastrophe of autism’ Merzenich turns to the research of Rita Levi-Montalcini, a young Jewish scientist who lived in fascist Italy before and during WWII. While in hiding, she built a secret laboratory in her bedroom and studied how nerves form. She discovered that the nerves of chick embryos grow faster in the presence of mice tumors. With the help of biochemist Stanley Cohen, they isolated a protein that they called NGF, or nerve growth factor. They eventually found similar compounds, one of which was BDNF, or brain-derived neurotrophic factor.
BDNF plays a critical role in brain plasticity, from stimulating neuron growth during learning to turning on the nucleus basalis during infancy and when we need to pay attention later in life. These steps are critical to forming new long-term brain maps and memories. And finally, BDNF is responsible for shutting down the nucleus basalis after the critical period of infancy. Levi-Montalcini later won a Nobel prize for her work.
Merzenich hypothesized that in autistic children, the BDNF is prematurely released, turning off the critical period too early, thus leaving a relatively undifferentiated brain map. In this situation, sensory input is overwhelming to the brain, which cannot distinguish between various sights and sounds. When a normal child hears a single tone, his differentiated brain map will only light up in the area dedicated to that tone. In the autistic child however, any sound, whether simple or complex, will light up the entire auditory cortex. The autistic child, with an undifferentiated brain map, is unable to know which sounds to ignore and which are important. The undifferentiated brain map has no filters. Without such filters, the child is continually overwhelmed and naturally withdraws from such sensory overload.
Next Merzenich investigated why the neurons of autistic children would become overexcited and release too much BDNF. Several studies suggested how environmental factors may contribute, such as the background noise, or ‘white noise’ of many urban settings. To test this theory in a lab, Merzenich exposed young rats to pulses of white noise throughout their critical period. The rat’s cortexes were devastated. As predicted, such exposure to white noise, which released massive amounts of BDNF, led to prematurely closing the critical period, thus leaving undifferentiated brain maps. Merzenich had produced autistic rats in his lab.
After much focus on the science of learning, Doidge turns to the relatively new science of unlearning. There is a completely different chemistry to unlearning, in which brain maps are suppressed in order to rewire and learn new things. Love and grief are two experiences in life that are known to allow unlearning. This process is necessary from an evolutionary perspective. Without it, our brains would become saturated and we could not learn new things. When we fall in love, massive amounts of our brain map must change to accommodate a new person into our lives, new routines, and necessarily let go of some old habits. When we lose a loved one, although we ‘know’ that the person is gone, we find it difficult to let go. According to Freud, we must call up memories one at a time, relive them, then let go. This process can take years as we unlearn that the person is alive.
Another time for massive brain change and unlearning is when we become new parents. In both love and as new parents, the neuromodulator oxytocin is released, allowing existing neuronal connections to melt away, making room for new connections. This powerful hormone is released during love-making, as parents nurturing children, and in women during childbirth and breast-feeding. In males, a hormone called vasopressin is released when they become a new father. So as a survival mechanism, oxytocin helps us overcome our individualistic tendencies. “The deepest meaning of sexual experience lies not in pleasure, but in the opportunity it affords to surmount the solipsistic gulf, opening the door to a relationship. It is the afterplay, not the foreplay that counts in building trust.”
We are next introduced to Edward Taub who pioneered the concept of contraint-induced therapy, or CI therapy. Taub discovered this concept after working in labs with monkeys. He noticed that if he cut the sensory nerve of a monkey’s hand, the animal would stop using the deafferented arm and simply use the other arm. The injured hand and arm would go unused for an extended period, so the brain maps for that hand would gradually be taken over by other areas. Suspecting that this could be reversed, Taub put the good arm of a monkey in a sling so that it could not be used. Forced to rely on the deafferented limb, the monkey gradually regained use of the damaged hand, and indeed the brain map for that hand was recovered.
Taub called this phenomenon ‘learned non-use.’ This is the process whereby we take the path of least resistance, or the easy way out. After extended periods of this, the more difficult way is gradually unlearned. When the easy way out is no longer an option, lo and behold, we can relearn the more difficult way. In therapy, Taub employs this principle by putting arms in slings, or other such methods to force patients to regain use of limbs or skills since lost.
To expand his concept of learned non-use, Taub deafferented the nerve of an monkey’s arm, then put this arm in a sling rather than the good arm. The theory was that with the bad arm in a sling, the monkey would not know it was damaged and therefore would not ‘learn’ that he could not use it. When Taub removed the sling after 3 months (the period of spinal shock from the procedure), the monkey was soon able to use the deafferented limb.
Taub has opened a clinic in Alabama, and claims great success in rehabilitating stroke victims, even years after the damage was done. Among the principles that Taub has learned from his clinic, is that practice of new skills should be ‘massed’, that is several weeks of intense practice, an hour or two per day, five days per week. This has shown to be more effective than less frequent practice spread over a much longer time, say a year. Further, practice should relate to everyday life and have a reward system. The Taub clinic has an online service called ‘AutoCITE’ for those who cannot go to their Alabama location.
Doidge covers the topic of OCD, extreme worriers and other bad habits and hypothesizes that such behavior is actually physiologically-based. Called brain-lock, behaviors such as OCD involve a complex neural web of three distinct areas of the brain. When we perceive a problem, the normal brain deals with it, acknowledges that it has been dealt with, then lets go of the issue. For example, we might worry that we left the water running in the bathtub. The normal person will go check the tub, turn of the water if necessary, then stop worrying. The person afflicted with OCD will check the tub, walk away, but still feel that he must check the tub again, just to make sure. He cannot let go of the issue, regardless of seeing the tub not running. What appears to happen in the OCD brain is that one part of this process becomes ‘sticky’, in that its feedback mechanism does not function properly. It is as if his brain is locked in a recurring loop.
In therapy, OCD patients learn to relabel anxiety attacks as a malfunction of their own brain rather than an external issue. By seeing the issue as their own OCD, they then learn to immediately refocus on a pleasant, unrelated thought. Gradually, the OCD patient can rewire his brain to lessen or even eliminate the OCD problem. The key here is that the struggle is not what the patient feels during an OCD attack, but rather what they do. By training themselves to recognize their OCD problem, and to react to it with a pleasant activity or thought instead of worry, the OCD symptoms will, over time, go away. This seemingly simple approach accomplishes two things, both in compliance with the laws of neuroplasticity: first, new neural pathways are formed and strengthened for a pleasant activity (fire together, wire together). Second, the old pathways for the OCD behavior are weakened through non-use, since ‘neurons that fire apart wire apart.’
Doidge next introduces us to Vilayanur Subramanian Ramachandran, who I will refer to as Rama for short. He is an M.D, a neuroplastician and a PhD in psychology, working for the University of California in San Diego. He prefers to study individual cases rather than large statistically significant studies. As he puts it “if I show you a pig that can speak English, would it really make sense for the skeptic to argue ‘but that is just one pig. Show me another and I’ll believe you.”
Rama is skeptical of complicated, fancy scientific equipment because of the time it takes to learn how to use it and because of what he calls “the distance between the raw data and the final conclusion.” This distance allows to much opportunity to massage that data, and humans are notoriously susceptible to self-deception.
Rama shows Doidge a large square box with a mirror inside. It looks like a prop for an amateur magic trick. Using just this box, he has solved the centuries-old mystery of phantom limbs and the pain they cause. Often when a person loses a limb, they will experience pain in that limb, even though the limb is no longer there, and even though they are well aware of that fact. This phenomenon has tortured soldiers and amputees for centuries.
Using the mirror box, Rama instructs one amputee who we’ll call Alex, to put his good right arm inside the box, then lean forward and slightly to the right so he can see the mirror image of that right arm. To Alex, the image looks like his left arm. As Alex moves the fingers on his right hand and watches the mirror, it appears that his left hand is moving, except that he doesn’t have a left hand. After working with the mirror box every day for a few short sessions over the course of four weeks, Alex no longer has pain. Rama has performed the first successful amputation of a phantom limb.
Doidge continues to describe how the brain controls our perception of pain and how this relates to phantom body parts whose brain map has been frozen in time. In one remarkable demonstration of these principles, an Australian scientist names Moseley worked with patients whose pain was so great they could not move their limbs in the mirror box. Moseley asked these patients to simply imagine moving their painful limbs, without actually executing the movements. He hoped this would activate brain maps for movement. They were shown pictures of hands in various positions and asked to imagine them for 15 minutes, three times per day. After the visualization exercises, they were able to use the mirror box, and within 12 weeks, half of the patients eliminated all pain, while some of the others had diminished pain.
Next we go to the lab of Alvaro Pascual-Leone in Boston. Alvaro uses a device called TMS to non-invasively measure precise brain activity, and also to stimulate areas of the cortex as Penfield has a century earlier. He puts the device a few inches from Doidge’s head, turns it on, and Doidge notices his index finger move. Alvaro has stimulated the cortical area controlling that finger.
Alvaro studied how our thoughts can manifest material changes in our brains. Alvaro taught a simple piano sequence to two groups of people who had never played that instrument. He showed them which fingers to move and let them hear the notes as they were played. Then the first group would sit in front of an electronic piano for two hours per day, for five days and imagine playing the sequence and hearing it played. The second group actually played the music for two hours per day also for five days.
Both groups had their brains mapped before the experiment, each day during it, and afterward. Then both groups were asked to play the sequence while a computer measured the accuracy of their performance. By the fifth day, changes in the motor signals were the same in both groups. When asked to physically play the piano, the imagine group performed at the same level that the physical group achieved on their third day. However after just one physical practice session, the imagine group caught up and could play as well as the physical group.
In a similar though extremely simple experiment, scientists showed that the act of imagining using one’s muscle will actually strengthen them. One group is told to do a certain finger exercises Monday through Friday for four weeks. The imagining group followed the same schedule, but simply imagined doing the exercises, and also imagined a coach shouting “harder, harder!” At the end of the study, the physical group increased muscular strength by 30%. The imaginary group increased their strength by 22%.
Alvaro has shown that the localizationist view is not really accurate. When a group of teachers in Spain were blindfolded for a week while teaching blind students, their visual cortexes began processing sound with two days. Such rapid neuroplastic change requires the presence of hidden pathways in the brain connecting many areas. Otherwise, neurons could not possibly grow fast enough to rewire from the auditory cortex to the visual.
There were many other stories in this book, all pointing to remarkable brain plasticity, though I will leave those for you to discover.