PDF Summary:The Brain That Changes Itself, by Norman Doidge

Your brain is always changing. As you’re reading right now, your brain is rearranging itself to process the information you’re taking in so you can understand and retain it. In The Brain That Changes Itself, psychoanalyst and best-selling author Norman Doidge uses case studies and centuries of research to provide a thorough but understandable explanation of the concept of neuroplasticity—the phenomenon of the changing brain.

In our guide, we’ll examine the development of the concept of neuroplasticity, how the brain changes itself in response to stimuli, how this impacts our functioning, and how we can use it to our advantage—as well as how it can sometimes work against us. We’ll also examine more recent research into the topic, plus how new technologies and treatments are using neuroplasticity to improve outcomes for people with neurological diseases and brain damage.

(continued)...

Learning How Maps Change: The Competition for Brain Space

It was clear now that, at least in infancy, the brain was capable of restructuring itself in response to something like the loss of a sense. According to Doidge, further studies involving brain mapping showed that brain maps constantly change, even without interventions like removing input from a sense or part of the body. Mapping an animal once and then doing so again months later showed changes in the maps every time, indicating that our brains change in the normal course of our lives.

(Shortform note: Early maps showed us the location of things like bodily functions and sensory perception and processing in the brain, but more recent research has allowed us to pinpoint where newly-learned concepts appear in the brain. Studies showed that when a group of people all learned the same new concept, the same regions of their brains were activated, showing exactly where that learning was taking place. Not only was this a big step forward from just mapping functions and sensory processing, it also showed that everything we learn causes permanent changes to our brains—which helps explain why repeated brain scans show that maps are constantly changing.)

One experiment using monkeys showed that the brain wasn’t “hard-wired” to have a specific structure, indicating that the brain must be plastic. In the experiment, scientists disconnected the monkey’s nerves that control their thumb and forefinger, then reversed them. But the nerves reorganized themselves so that the monkey could still control its thumb and forefinger just as well as before.

Additional research led to the discovery of competitive neuroplasticity. According to Doidge, this means if a nerve stops working (is cut), the area of the brain that is connected to that nerve doesn’t just waste away. Instead, since the brain only has so much mass to perform all its different functions, the nerves that still work will use that leftover brain space, showing that there’s competition for limited resources within the brain. If you don’t use an area of the brain for its original purpose, it may be taken over by other functions you do still use.

To discover this, researchers again used monkeys as test subjects: They disconnected the nerve that controls the middle of the hand, or the median nerve, so that it wouldn't receive any input from the middle of the hand. As expected, when the middle of the monkey’s hand was touched, the brain area connected to the median nerve no longer lit up. However, touching other areas of the monkey’s hand that were controlled by different nerves did cause that brain area to light up, meaning that brain area was now being used to detect input from those other nerves.

Competitive Plasticity and Human Development

Competitive brain plasticity may help explain why humans lack certain senses that other animals have, such as infrared vision or ultrasonic hearing. If these skills weren’t necessary for our survival, our brains never made space for them, so our species never developed them. Humans have greater cognitive capacity—and often larger brains proportional to our body weight—than animals and therefore need more bodily resources to sustain that cognitive capacity.

This higher cognitive capacity and the large brains required to store it may also explain why humans are born helpless compared to so many other creatures. While some animals like horses and chickens are able to stand and walk immediately after birth, human babies are born so weak they can’t even lift their heads. Scientists believe this is because of different gestational periods—while horses, for example, are pregnant for 11-12 months, human infants must be born around the nine-month mark in order for their heads to fit through the birth canal, which is smaller in humans because we’re bipedal.

Additionally, being pregnant increases a person’s metabolic needs, and research suggests that a human’s metabolism wouldn’t be able to sustain a fetus past nine months of pregnancy. Therefore, our high cognitive capacity requires much more development post-birth compared to most other animals.

Training the Brain: Applications for Restoring Function

As we’ve seen, research showed that the neural connections in the brain were changing constantly and that they could even move around in the brain or disappear entirely depending on the functions demanded of the brain. According to Doidge, this meant that new connections must be forming between neurons that weren’t previously connected. Scientists realized that the brain’s ability to form new connections meant they might be able to treat or even cure things like learning disabilities and severe brain damage by training the neurons to fire in a more desirable way.

(Shortform note: The ability of brain maps to disappear entirely can cause us to lose certain abilities or skills, and these losses may be accelerated by our growing technology. The human brain has a lot of space devoted to navigation, for example, but since the invention of GPS, people have been using that part of their brains less. This has led our mental navigation systems to become less active, and consequently, other abilities like spatial awareness and certain types of memory are becoming weaker. Scientists are researching ways that GPS technology could be modified so that we can still use it to find our way around while also practicing the navigation skills that strengthen our memory and spatial awareness.)

According to Doidge, a series of experiments by Edward Taub proved that we can train neurons to control a body part that doesn’t have sensory input. The experiments involved deafferenting the arms of monkeys: cutting sensory nerves so that the brain didn’t receive any sensation from the arms. Previous experiments with deafferenting monkeys showed that if one arm was deafferented, the monkey would only use the healthy arm, leading scientists to believe that motor control was dependent on sensation—once the neural connections for sensation were disconnected, the neural connections for movement became unusable.

Doidge says that Taub discovered the reason a monkey with one deafferented arm would begin using the healthy arm exclusively was because of learned nonuse. After surgery on the spinal cord, the neurons have trouble firing correctly—a condition called spinal shock, which results from damage to the spinal cord and usually lasts two to six months. An animal in spinal shock will try to use its deafferented arm, but because the neurons aren’t firing well, it will frequently fail to get the response it wants and eventually give up trying. It will learn to not use its deafferented arm and to use only the healthy one instead, thereby reinforcing only those neural pathways to the healthy arm while the pathways to the deafferented arm fall into disuse.

(Shortform note: Since spinal shock is the result of damage to the spinal cord, it usually only occurs in those who’ve experienced a severe spinal cord injury. Deafferentation is performed by cutting the nerve right where it connects to the spinal cord, so this is why deafferentation would result in spinal shock while most surgeries and procedures would not.)

A Global Definition of Learned Nonuse

While the phenomenon of learned nonuse is well established in the medical field, scientists are still working on creating a clear definition of learned nonuse that would apply across all scientific disciplines and an objective way to diagnose it. Experts suggest that it’s characterized by a difference in the brain’s ability to deliberately perform a motor function on demand and its ability to perform that function spontaneously, that is, without a conscious effort to use a body part that is harder to use. In other words, someone experiencing learned nonuse of the right arm can deliberately pick up a glass with their right hand, but they wouldn’t reach for it automatically with their right hand—they’d use their left.

Since things like which arm we favor to perform certain tasks is often an unconscious choice, eliminating learned nonuse first requires a conscious effort to use the affected body part instead of compensating with a body part that has no functional impairment.

However, further experiments showed that learned nonuse could be prevented by restraining the deafferented limb until spinal shock wore off, because while the arm was restrained the monkey wouldn’t try—and fail—to use it, so once the restraint was taken off, it soon used its arm just like it had before surgery.

(Shortform note: We can infer from Doidge’s description that the reason a monkey can still use its limb after restraining it during spinal shock is that it’s aware of a physical constraint restricting its movement, so it doesn’t try to use it. The neural pathways for that limb therefore remain in place and the monkey doesn’t learn that the limb doesn’t work, as it would if it tried and failed to move an unrestrained limb.)

Taub also found that learned nonuse could be corrected if he forced a monkey to use its deafferented arm by restraining the healthy arm, and that it could even be corrected years after the deafferentation was performed. This had major implications for stroke victims who had lost movement in certain body parts, as we’ll see in the next section.

(Shortform note: While correcting learned nonuse can restore the use of an impaired body part, research suggests that if it’s done too soon after injury, it may do more harm than good. Experiments on animals showed that restraining the healthy limb immediately after an injury could cause forced overuse, which can result in increased brain damage and hinder recovery. It’s possible there is an optimal period for this type of therapy after a stroke or injury that would provide the greatest gains without exacerbating the problem.)

How Can Neuroplasticity Improve Our Lives?

Doidge says that neuroplasticity means we can change our brains to suit our needs. This has resulted in huge developments in neuroscience that have helped many people recover motor, sensory, and cognitive functions they had lost. Let’s look at some instances of such recovery.

Help for Stroke Patients

According to Doidge, Edward Taub used his research with monkeys to develop a treatment for regaining motor control called constraint-induced movement therapy, or CI therapy. If a patient loses the ability to use one of their arms—a common result of strokes—this therapy re-teaches them to use it by constraining their good hand. Being forced to use their affected hand in everyday activities causes the brain to rewire itself to make those movements possible and then easier.

(Shortform note: New technology is being developed that could complement or substitute for Taub’s CI therapy: Scientists have created a virtual reality interface that allows stroke patients to “practice” performing everyday activities. Using their brain to control an artificial hand, the patients can see themselves performing these tasks, and the activities are shown to retrain their brains to use their impaired limbs or body parts similarly to the way Taub’s therapy retrains the brain.)

Taub’s therapy regimens are founded on three principles: training with activities we do in everyday life is more effective; training should be incremental; and training is most effective in massed practice. This means the training should be done in short, concentrated periods, which is more effective than training over a long period of time with less frequency.

(Shortform note: Massed practice appears to be effective specifically in reorganizing the brain to use an impaired body part. However, research suggests that for learning more complex tasks, massed practice may be less effective than distributed practice, which is carried out over a longer period of time with more breaks in between practice sessions. Distributed practice also seems to be more effective for learning and retaining new information and knowledge.)

Help for Patients With Balance Loss

Because plasticity can allow the brain to substitute one sense for another, it can also help someone to regain a lost sense such as balance. Balance, or the vestibular sense, tends to weaken as we age, leading to more frequent falls. Balance issues can also occur from brain damage.

In order to restore a patient’s sense of balance, neuroscientists use a device called an accelerometer to stimulate the patient’s tongue according to the movement of their head, letting them sense a change in their balance through the sensations on their tongues.

When patients use this device, new connections form between their balance system and their tongue. This provides a residual effect, so even when they take off the device, their new balance system keeps going for a while. The more and longer the device is used, the longer the residual effect, and it can eventually become permanent, fixing the patient’s balance issues entirely.

Other Solutions for Balance Issues

In addition to the accelerometer Doidge describes, scientists have developed other devices and methods of substituting another sense for a patient’s sense of balance.

Part of our ability to balance comes from fluid canals in our ears that let us know if our bodies are moving or leaning in a given direction. Inner ear diseases and infections can interfere with this system. For balance issues resulting from inner ear damage, researchers are studying technology that could retrain the brain’s balance system by applying electrical stimulation to the ears’ fluid canals in response to the body’s movement using a prosthesis or implant.

Other researchers are working on developing a type of insole that would apply small vibrations to the soles of the feet to help detect changes in movement. This treatment could be particularly effective in patients who have sensory loss in their extremities, as research has already established that these types of vibrations can help restore sensation in the feet.

A third type of technology being developed uses sound to substitute for the vestibular sense: It detects a person’s movement and makes a sound when they lean in a certain direction. The patient can tell if they’re leaning forward or backward by the pitch of the tone, and they can tell left from right depending on which ear they hear the tone in. The tone grows louder the further they lean.

Help for Patients With Phantom Limbs

Doidge says people with phantom limbs can also benefit from neuroplastic intervention. The term phantom limb refers to a sense of still having a limb that has been lost. So, for example, if you’ve had a leg amputated, you may develop a phantom leg that you can still feel as if the real leg were there. You may feel pain, pressure, or other sensations like itching, and you may also feel the physical sensation of moving that leg even though it’s not there anymore.

Some amputated limbs feel like a dead weight—like the limb is still there but is paralyzed or frozen. This happens because a limb is often immobilized with a cast or sling for a long time before the amputation. Scientists believe that the brain continues to send motor commands to it, only to receive no response to show that the limb is moving. Then, once the limb is amputated, the brain map that developed while it was immobilized—where the brain sends signals and the limb doesn’t respond—becomes fixed, and the brain continues to feel like the limb is there but is frozen or paralyzed.

Phantom pain works similarly. The brain continues to send commands to the amputated limb but receives no response, so the commands increase. The brain tries so hard to move the amputated limb that it causes the pain that your brain associates with trying too hard to move it (like how your hand hurts if you clench it too hard). According to Doidge, 95% of people who have a limb amputated suffer from long-term phantom pain.

To eradicate phantom pain, a device called a mirror box, developed by Vilayanur Subramanian Ramachandran, allows a patient who’s lost an arm to “see” their phantom arm by mirroring their good one. The box has two sections divided by a mirror. The patient places their existing arm into one section of the box and is then told to imagine putting their phantom arm into the other section. They then watch the reflection of their good hand and arm moving, which makes it look like their other arm is moving as well, and soon this causes them to feel like their phantom arm is moving along with the reflection. This ability to “move” their phantom arm helps relieve the pain they’re feeling, and over time, use of the mirror box can make the feeling of the phantom limb go away entirely.

(Shortform note: Ramachandran’s mirror box has proven to be very effective in treating phantom arms and pain, but new virtual reality technology may provide a solution that is more accessible and effective than the mirror box. By wearing a pair of VR goggles and a glove, plus electrodes on the stump of the missing limb, patients can not only see their missing limb being used as they play various games that involve both hands, they can also feel it thanks to the stimulation provided by the electrodes attached to their stump. Further research seeks to expand this technology to be applicable to lower body amputations as well.)

Leftover Brain Maps and Phantom Pain

The phenomenon of phantom limbs seems to fly in the face of what we know about neuroplasticity and the brain’s ability to rewire itself in response to changes: If we lose one of our limbs, it seems the brain should reorganize itself so that the maps devoted to controlling that limb become dormant or disappear entirely. However, research has shown that our brains can retain their maps for a missing hand for over three decades after the loss of the hand. While the reason for this isn’t fully understood, it may be useful in the development of brain-controlled prostheses, as the brain may be able to adapt to such a prosthesis with minimal retraining.

Phantom pain also seems to be directly linked to these retained maps: The stronger the brain’s representation of the missing body part, the more intense phantom pain they experience. In many cases of severe pain from phantom hands, the brain’s representation of the missing hand is just as clear and strong as the representation of their remaining hand. However, there also seem to be fewer connections in these patients between the representation of the missing hand and the rest of the brain, so while the brain’s image of the hand remains strong, it's often out of sync with the rest of the brain.

Help for Patients With Learning Disorders

Neuroplastic research may even allow us to “cure” learning disabilities, asserts Doidge. By studying what areas of the brain are affected by a disability, we can create specific types of mental exercises to strengthen those areas and treat the disability. People who struggle with speaking, reading, and writing often have issues in their premotor cortex, for example, and can benefit from exercises that strengthen that part of the brain. These might include tracing exercises, which involve tracing complex characters or lines to stimulate the neurons in the premotor cortex. People who have issues with auditory processing—understanding and remembering spoken information—may benefit from memorizing poems and stories.

(Shortform note: The idea that learning difficulties stem from individual parts of the brain has been well established, but recent research suggests this premise might be flawed. Instead, according to a recent study, these difficulties seem to come from poor connections between different parts of the brain. This suggests that learning disabilities are less the result of a single part of the brain struggling to process information and more the result of the brain having difficulty sharing information between different brain areas. Though this conflicts with Doidge’s explanations, it may help explain why something like speech can be improved through tasks as seemingly unrelated as tracing unfamiliar characters.)

A regimen like this is highly individualized. Doidge suggests that providing all children, regardless of disability, with an individualized plan that targets their weak areas could vastly improve their education and abilities later in life.

He also suggests that implementing these plans early can make a big difference, because otherwise the child will often attribute their weaknesses to “stupidity,” start to dislike learning, and avoid the activity they struggle with, which prevents them from getting stronger in that area.

(Shortform note: Doidge’s suggestion that all children would benefit from individualized learning that focuses on their unique needs and gifts is supported by research into both learning disabilities and giftedness. Research shows that students whose learning disabilities aren’t accommodated experience stress from their academic struggles at school, and students whose giftedness isn’t accommodated experience understimulation. Both situations can lead to behavioral problems and a dislike of school, and both can be avoided through more personalized education like what Doidge describes. Unfortunately, personalization requires a great deal of resources—more than are currently available to public schools in the US.)

Drawbacks of Neuroplasticity

Unfortunately, brain plasticity may have downsides, says Doidge. Because, as we’ve discussed, plasticity is competitive, when one area of the brain becomes unused, it’s likely to be taken over by other functions that are used regularly. This can make it difficult to break bad habits because using the pathways involved with those habits not only strengthens them, but also weakens the pathways that are not used by the bad habit.

(Shortform note: This pattern of engaging in a bad habit, strengthening that habit, and weakening good habits can create a harmful feedback loop: Any time a habit is triggered, you’re more likely to engage in that habit, which further reinforces the association of that habit with that same trigger. To break this loop and the bad habits it entails, experts recommend quitting bad habits cold turkey so you stop reinforcing them and then replacing them with good habits so those pathways get strengthened instead. If quitting cold turkey is too difficult or dangerous, you can still replace the bad habits with good ones using incremental steps.)

This also applies to learning a second language: The reason adults have more trouble learning a second language than children do is that the areas of their brain that process language are already being used to process their first language. It therefore takes more practice for an adult than for a child to create new pathways in that area to correspond to a second language. It’s easier to learn a second language while you're acquiring your first language because the map of neural pathways for language widens to include both languages as they develop at the same time. However, when you’re learning a second language as an adult, that new language has to develop a brand new neural map rather than incorporating it into the first language’s map.

(Shortform note: Other research suggests that learning a language in childhood may be easier because of brain lateralization—the tendency of the brain to use either the left or right hemisphere more than the other in certain processes. Experts say that, during the critical period in childhood, the brain is able to use both hemispheres in learning language because it's more plastic, whereas in adulthood, that learning would likely be specialized to the left hemisphere, which may reduce its connection to other parts of the brain and thus make learning harder.)

Doidge also suggests that neuroplasticity could be responsible for excessive worry and disorders like obsessive compulsive disorder. As your brain continually plays through anxiety-inducing scenarios, those pathways become stronger, which means you worry about them even more.

Though it may be the cause, Doidge also says that neuroplasticity could be the cure for excessive worry and obsessive compulsive disorder. Therapy that involves reframing the worrisome thoughts into something positive, or distracting yourself with something positive, can help weaken the worry pathways that have become so strong.

(Shortform note: Other research into obsessive compulsive disorder suggests that distraction from worry may not be as effective as thinking about your worry through metacognition. Rather than diverting your attention away from your obsessive thoughts, metacognition based on doubt therapy is designed to make you more comfortable with the uncertainty underlying those thoughts—for example, if you compulsively wash your hands because you always doubt they’re fully clean, this therapy would give you step by step instructions for becoming more comfortable with the idea that your hands might not be fully clean. While the approach is different, this method would also weaken the brain pathways involved in worry.)