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

In Chapter 10, Doidge shows the brain remains plastic even in old age, and there are benefits to using mental exercises to keep the brain active. Recent research shows humans have neuronal stem cells that are active until death, which means humans can produce new neurons to replace old ones. This chapter opens with an interview with 90-year-old Dr. Stanley Karansky, who exercises both his body and mind: He does muscle training three times per week and plays computer games created by Michael Merzenich’s Posit Science team. Though the exercises focus on training auditory memory, he has reaped additional benefits from being alert, like the children who practiced with Fast ForWord. Karansky’s family does not have a history of longevity, so he credits much of his current physical and mental health to his own efforts.

For years, scientists have wondered why animals such as lizards have neuronal stem cells, which can divide into new neurons to replace old ones. Nobel Prize–winning neuroanatomist Santiago Ramón y Cajal has spent his life searching for human stem cells, to no avail. Doidge again suspects lingering bias about the brain as slowing progress in this area. In 1998, neuroscientists Frederick Gage and Peter Eriksson made a breakthrough: They found human stem cells in the hippocampus. These cells are “neuronal” because they have yet to differentiate into neurons. This is why they can endlessly divide in a process called “neurogenesis” and supply new neurons. Dissection of patients who donated their bodies to science revealed neuronal stem cells were still active until their passing. Since Gage and Eriksson’s discovery, researchers found more stem cells in the olfactory bulb, septum, striatum, and spinal cord.

Gage and Eriksson then studied how to increase the total amount of neuronal stem cells. This can be done by either generating new cells or prolonging the lives of existing cells, and both methods can work simultaneously. Gage’s research team found that lab mice with a stimulating environment underwent greater neurogenesis. They suspect the mice’s running creates anticipatory proliferation, which prepares the brain to learn and respond to new experiences. Similarly, humans who wish to keep their brains fit must learn new skills rather than repeat skills. New research has shown that people who are better educated and both physically and socially active are less likely to suffer dementia. Doidge ends the chapter by encouraging older readers to continue exercising their plastic brains. Although general decay is unavoidable, older people who develop new skills can make the best of the plastic brain to become healthier.

This final chapter describes the case of Michelle Mack, a woman who was born without the left hemisphere of her brain but learned to use the right hemisphere in its stead. Michelle’s case proves individuals are more than the sum of their parts: She learned to adapt and now leads a relatively normal life. Without the technology to do detailed scans at the time, Michelle’s parents originally did not realize their infant sustained brain damage in the womb. Michelle did not learn to turn over, and her right hand remained clenched, as if partially paralyzed. She did not learn to crawl and only reached for things with her left hand; she also did not follow moving objects with her eyes. At one year old, Michelle learned to unclench her right hand and began to track movement. At two years old, she finally started speaking. She was initially diagnosed with significant delay in development, and it was not until she turned six that CAT scans became advanced enough to show her missing left hemisphere. Growing up, Michelle had learning difficulties in certain areas and excelled in others. She has difficulty seeing things on her right side, but can clearly hear from a certain distance. She cannot quickly process abstract thoughts, but can remember details about every day of her life stretching back 18 years.

Doidge surmises Michelle’s difficulty with abstract thoughts is the result of an overcrowded right hemisphere, which had to process speech and relate symbols in the left hemisphere’s stead. When he asks her to explain proverbs, she can usually recite their learned meanings, but struggles when pressed to elaborate. She works with neuroscientist Jordan Grafman of the NIH to understand how her brain works, with Grafman having first encountered neuroplasticity when he helped a woman, Renata, recover from paralysis after being strangled. This injury damaged her neurons, motor cortex, and hippocampus because it cut off the brain’s oxygen source; she lost her independence and developed severe memory problems. Grafman’s team helped Renata recover her movement and memory through intensive rehabilitation, and though she never fully recovered, her improvements were sufficient to convince Grafman of neuroplasticity.

Grafman later became the director of the neuropsychological branch of the Vietnam Head Injury Study, where he studied soldiers who sustained injury in their frontal lobes—the area responsible for decision-making, forming goals, and prolonged focus. His research revealed soldiers who initially performed well on the Armed Forces Qualification Test (which is similar to an IQ test) had a better chance of recovery. However, since each brain injury is unique in size, location, and damage, he developed an interest in studying individual cases rather than larger groups. Grafman theorizes the neurons in the center of a given area are the most active and committed to the function processed by that area. Neurons closer to the periphery are more easily recruited by adjacent areas to perform different tasks, thus creating an atmosphere of competition for limited resources.

To Grafman, the four categories of neuroplasticity are “map expansion” (recruiting bordering neurons to perform different tasks), “sensory reassignment” (encouraging inactive neurons to perform a different task), “compensatory masquerade” (substitution), and “mirror region takeover” (which is the case for Michelle, whose right hemisphere took on the left’s tasks). His patient, Paul, sustained an injury to his right hemisphere but had difficulty doing arithmetic, which is usually processed in the left. Grafman theorized Paul’s injury, which happened when he was seven months old, left his parietal lobe lacking basic visual-spatial processing to navigate the material world. Although brains tend to prefer specificity, Michelle and Paul’s cases show infancy is without specialization. Thus, in critical periods of high plasticity, mental functions can migrate as far as the opposite hemisphere.

Grafman also hypothesizes that humans, unlike other animals, developed larger prefrontal lobes, which help them store long-term information. The left prefrontal lobe remembers individual events, while its mirror distinguishes a pattern to learn a lesson. Together, they impart an evolutionary advantage: the power of foresight. Michelle, who is missing her left prefrontal lobe, often has difficulty controlling her impulses and anticipating the future. Losing this ability can prevent connections, but she is content with the way she is: When Doidge asks what her heaven looks like, she envisions a world devoid of sadness, where her family is present but distant enough that she can remain independent. Likewise, art teacher Betty Edwards’s book, Drawing on the Right Side of the Brain, actively teaches students to inhibit their “logical” left hemisphere. She once asked students to sketch an item by looking at it, then turned the object upside down and asked the students to repeat the exercise. She found that they drew more faithfully when the object was upside down because they ceased to think of it from a “logical” standpoint.