The Brain That Changes Itself: Stories of Personal Triumph from the Frontiers of Brain Science

by Norman Doidge

The tongue is what he calls the ideal “brain-machine interface,” an excellent entry point to the brain because it has no insensitive layer of dead skin on it.

One of the great discoveries Penfield made was that sensory and motor brain maps, like geographical maps, are topographical, meaning that areas adjacent to each other on the body’s surface are generally adjacent to each other on the brain maps. He also discovered that when he touched certain parts of the brain, he

triggered long-lost childhood memories or dreamlike scenes—which implied that higher mental activities were also mapped in the brain.

Merzenich discovered that these maps are neither immutable within a single brain nor universal but vary in their borders and size from person to person.

It also seemed that each neural system had a different critical period, or window of time, during which it was especially plastic and sensitive to the environment, and during which it had rapid, formative growth.

Language development, for instance, has a critical period that begins in infancy and ends between eight years and puberty. After this critical

period closes, a person’s ability to learn a second language without an accent is limited. In fact, second languages learned after the critical period are not processed in the...

It is important to understand that the nervous system is divided into two parts. The first part is the central nervous system (the brain and spinal cord), which is the command-and-control center of the system; it was thought to lack plasticity. The second part is the peripheral nervous system, which brings messages from the sense receptors to the spinal cord and brain and carries messages from the brain and spinal cord to the muscles and glands. The peripheral nervous system was long known to be plastic; if you cut a nerve in your hand,

it can “regenerate” or heal itself.

They micromapped the hand maps in the brains of several adolescent monkeys, cut a peripheral nerve to the hand, and immediately sewed the two severed ends close together but not quite touching, hoping the many axonal wires in the nerve would get crossed as the nerve regenerated itself. After seven months they remapped the brain. Merzenich assumed they would see a very disturbed, chaotic brain map. Thus, if the nerves for the thumb and the index finger had been crossed, he expected that touching the index finger would generate activity in the map area for the thumb. But he saw nothing of the kind. The map was almost normal.

If the brain map could normalize its structure in response to abnormal input, the prevailing view that we are born with a hardwired system had to be wrong. The brain had to be plastic.

“One day’s mapping would no longer be valid on the morrow.” Maps were dynamic.

Because the area was still so controversial, he did his plasticity experiments in the guise of more acceptable research. Thus he spent much of the early 1970s mapping the auditory cortex of different species of animals, and he helped others invent and perfect the cochlear implant.

A cochlear implant is not a hearing aid. A hearing aid amplifies sound for those who have partial hearing loss due to a partially functioning cochlea that works well enough to detect some sound. Cochlear implants are for those who are deaf because of a profoundly damaged cochlea.

The implant replaces the cochlea, transforming speech sounds into bursts of electrical impulses, which it sends to the brain. Because Merzenich and his colleagues could not hope to match the complexity of a natural organ with three thousand hair cells, the question was, could the brain, which had evolved to decode complex signals coming from so many hair cells, decode impulses from a far simpler device? If it could, it would mean that the auditory cortex was plastic, capable of modifying itself and responding to artificial inputs.

There is an endless war of nerves going on inside each of our brains. If we stop exercising our mental skills, we do not just forget them: the brain map space for those skills is turned over to the skills we practice instead. If you ever ask yourself, “How often must I practice French, or guitar, or math to keep on top of it?” you are asking a question about competitive plasticity. You are asking how frequently you

must practice one activity to make sure its brain map space is not lost to another.

that timing of the input to the neurons in the map was the key to forming it—neurons that fired together in time wired together to make one map.

if you separate the signals to neurons in time, you create separate brain maps.

as Neurons that fire apart wire apart—or Neurons out of sync fail to link.

when an animal is motivated to learn, the brain responds plastically. The experiment also showed that as brain maps get bigger, the individual neurons get more efficient in two stages. At first, as the monkey trained, the map for the fingertip grew to take up more space.

But after a while individual neurons within the map became more efficient, and eventually fewer neurons were required to perform the task.

This more efficient use of neurons occurs whenever we become proficient at a skill, and it explains why we don’t quickly run

out of map space as we practice or add skills to our repertoire.

Finally, Merzenich discovered that paying close attention is essential to long-term plastic change. In numerous experiments he found that lasting changes occurred only when his monkeys paid close attention. When the animals performed tasks automatically, without paying attention, they changed their brain maps, but the changes

did not last. We often praise “the ability to multitask.” While you can learn when you divide your attention, divided attention doesn’t lead to abiding change in your brain maps.

The mystery of autism—a human mind that cannot conceive of other minds—is one of the most baffling and poignant in psychiatry and one of the most severe developmental disorders of childhood.

he had a hunch that something might be going wrong in infancy, when most critical periods occur, plasticity is at its height, and a massive amount of development should be occurring. But autism is largely an inherited condition. If one identical twin is autistic, there is an 80 to 90 percent chance the other twin will be as well. In cases of nonidentical twins, where one is autistic, the nonautistic twin will often have some language and social

problems. Yet the incidence of autism has been climbing at a staggering rate that can’t be explained by genetics alone. When the condition was first recognized over forty years ago, about one in 5,000 people had it. Now Merzenich believes it is at least fifteen in 5,000.

That’s why learning a new language in old age is so good for improving and maintaining the memory generally. Because it requires intense focus, studying a new language turns on the control system for plasticity and keeps it in good shape for laying down sharp memories of all kinds.

To keep the mind alive requires learning something truly new with intense focus.

“Everything that you can see happen in a young brain can happen in an older brain.” The only requirement is that the person must have enough of a reward, or punishment, to keep paying attention through what might otherwise be a boring training session. If so, he says, “the changes can be every bit as great as the changes in a newborn.”

Plastic change, caused by our experience, travels deep into the brain and ultimately even into our genes, molding them as well—a topic to which we shall return.

One of his most important contributions was his discovery of critical periods for sexual plasticity. Freud argued that an adult’s ability to love intimately and sexually unfolds in stages, beginning in the infant’s first passionate attachments to its parents.

We are unable to distinguish our “second nature” from our “original nature” because our neuroplastic brains, once rewired, develop a new nature, every bit as biological as our original.

Nondrug addictions, such as running and sucrose drinking, also lead to the accumulation of ΔFosB and the same permanent changes in the dopamine system.

Sooner or later the surfer finds a killer combination that presses a number of his sexual buttons at once. Then he reinforces the network by viewing the images repeatedly, masturbating, releasing dopamine and strengthening these networks. He has created a kind of “neosexuality,” a rebuilt libido that has strong roots in his buried sexual tendencies.

A drug like cocaine acts on us by lowering the threshold at which our pleasure centers will fire, making it easier for them to turn on. It is not simply the cocaine that gives us pleasure. It is the fact that our pleasure centers now fire so easily that makes whatever we experience feel great.

falling in love also lowers the threshold at which the pleasure centers will fire.

When a person gets high on cocaine, becomes manic, or falls in love, he enters an enthusiastic state and is optimistic about everything, because all three conditions lower the firing threshold for the appetitive pleasure system, the dopamine-based system associated with the pleasure of anticipating something we desire.

When monogamous mates develop a tolerance for each other and lose the romantic high they once had, the change may be a sign, not that either of them is inadequate or boring, but that their plastic brains have so well adapted to each other that it’s harder for them to get the same buzz they once got from each other. Fortunately, lovers can stimulate their dopamine, keeping the high alive, by injecting novelty into their relationship. When a couple go on a romantic vacation or try new activities together, or wear new kinds of clothing, or surprise each other, they are using novelty to turn on the pleasure centers, so that everything they experience, including each other, excites and pleases them.

We must be learning if we are to feel fully alive, and when life, or love, becomes too predictable and it seems like there is little left to learn, we become restless-a protest, perhaps, of the plastic brain when it can no longer perform its essential task.

We grieve by calling up one memory at a time, reliving it, and then letting it go.

Oxytocin is sometimes called the commitment neuromodulator because it reinforces bonding in mammals. It is released when lovers connect and make love—in humans oxytocin is released in both sexes during orgasm—and when couples parent and nurture their children.

A similar brain trap occurs in Japanese people who, when speaking English, can’t hear the difference between r and l because the two sounds are not differentiated in their brain maps. Each time they try to say the sounds properly, they say them incorrectly, reinforcing the problem.

Sometimes after an injury, because the nerves for touch, temperature, and pain are so close together, there can be cross-wiring errors. So, Ramachandran wondered, might a person who is touched, in cases of cross-wiring, feel pain or warmth? Could a person who was touched gently on the face feel pain in a phantom arm?

Not all phantoms are painful. After Ramachandran published his discoveries, amputees began to seek him out. Several leg amputees reported, with much shame, that when they had sex, they often experienced their orgasms in their phantom legs and feet. One man confessed that because his leg and foot were so much larger than his genitals, the orgasm was “much bigger” than it used to be.

How much pain we feel is determined in significant part by our brains and minds—our current mood, our past experiences of pain, our psychology, and how serious we

think our injury is.

Maps can also enlarge their receptive field, coming to represent more of the body’s surface, increasing pain sensitivity. As the maps change, pain signals in one map can “spill” into adjacent pain maps, and we may develop “referred pain,” when we are hurt in one body part but feel the pain in another. Sometimes a single pain signal reverberates throughout the brain, so that pain persists even after its original stimulus has stopped.