Until the last few decades, everyone thought that the brain does not grow after puberty. Unlike the liver and other organs that can regenerate, it was thought that the adult brain does not generate new cells and does not have the capacity to repair itself when injured. We were familiar with diseases of the brain, such as Alzheimer’s, that shrink the brain as cells die, but we were not familiar with brain growth. Simply put, the dogma was that the best we could hope for was the brain structure remaining fixed throughout adult life. But there was no chance of the brain changing.
Paula Tallal, a professor of neuroscience at Rutgers University in New Jersey, helped prove that dogma wrong. When Tallal started her research, there had already been some pioneering experimental work done by Michael Merzenich, professor of neuroscience at University of California San Francisco, and other scientists showing that certain brain cells could change their functioning in response to injury.[i] For example, evidence was starting to accumulate that healthy areas of the brain could take up some of the functioning of damaged areas following stroke. These changes in nerve-cell functioning were termed “plastic” changes, and the new field of brain science was called “neuroplasticity.” Tallal teamed up with Merzenich to try something new. Tallal’s area of expertise was learning disorders, and she observed that many children cannot learn properly because they have trouble processing sounds, such as telling the difference between ba and da. By the time the child figures out what the teacher said, the teacher has already said the next sentence, and the child cannot follow. The same may be true for adults with hearing impairment, which is common in seniors. For children, this makes school very difficult, and for adults, such a problem could make it hard to understand a phone conversation, radio broadcast, or other speech where you cannot lip-read. When sound enters the ears, it gets converted to nerve signals by the cochlea, which then sends the signal to a dedicated brain area for processing sound. There, in the auditory cortex, the brain figures out whether the sound was—for example, ba or da.
In a landmark study published in 1996, Tallal and Merzenich showed that you can train the brain to work better and process the sound faster.[ii] By using computer exercises that adapted to each person’s sound-processing performance, they showed that the ability to distinguish similar sounds improved and the brain areas involved underwent change. They went on to form two San Francisco–based companies to provide practical help to improve brain performance, one that develops computerized brain training to help children, Scientific Learning Corporation, and another focused on adults, Posit Science. Many similar companies and institutions of learning have developed computerized training and education programs with similar goals.
Clinical research studies of these various training methods are starting to show results, but the jury is still out on which methods and specific products are effective, how effective they are, what situations they are good for, and if brain training can prevent or delay brain disease. The million-dollar question that is always in the background is whether and how we can train the brain to produce lasting and generalized improvement in brain function, not simply better performance on the specific game or exercise that is used for the training. In other words, can these fancy science-based programs do more than just make you a better Sudoku player?
There is reason to be optimistic. Evidence from the Bronx Aging Study published in the New England Journal of Medicine by Dr. Joseph Verghese and his team in 2003 has shown that people who do more leisure activities that demand mental work, such as board games or ballroom dancing, had a reduced risk of developing dementia, albeit only slightly.[iii]
Neuroplasticity is still a young field with much to learn. Nonetheless, there is impressive evidence for numerous ways that the adult brain changes. These changes occur all the time, and not just in response to injury. For example, when you learn a new skill, such as playing an instrument, the brain circuits that are involved in music become strengthened with more connections between the cells. If you learn how to juggle, requiring increased coordination between right and left hands, the connections between the right and left sides of the brain become thicker and more efficient.
The human brain somehow has the machinery to adjust according to the activity. Classic studies by neuroscientists, including Eric Kandel and Eve Marder using simple animals like the sea slug and crab, individual synapses and whole circuits can change function depending on the activity level. From the studies in people, we can see that these adjustments are not just quantitative, with more activity of the same circuits, but qualitative as well, with activity of improved circuits or different circuits entirely.
Another source of brain plasticity is also on the scientific frontier. The brain sometimes produces undifferentiated stem cells that can travel to where they are needed in the brain, and there they undergo specific development to fill the roles of different types of neurons. These stem cells are thought to be important for recovery from brain disease and possibly also for the maintenance of healthy functioning of the brain.
Brain plasticity has exciting implications for how the brain works. Because this field is still in its infancy, we do not know much about the basic principles. How much change can occur when we learn, practice, and master new skills? How much does the brain change when we adopt new thinking patterns, such as becoming more tolerant of others? What about when we change our ethical or moral behaviors, such as following through on a New Year’s resolution to give more charity? And, yes, the question that is often asked to neurologists—can we train our brains to improve memory and fight off Alzheimer’s disease? Paula Tallal and the other pioneers in this field have only just scratched the surface.
This piece was adapted from my book Embracing the Unknown: A Fresh Look at Nature and Science. Neuroplasticity is just one amazing feature of nature. The more we learn about nature, the more we can see how little we really understand. That gap in understanding is a source of awe – the intellectual realization that drives emotional rapture. Appreciate the living in the amazing world that we have been provided with. Stay tuned for more ...
[i] Jon H. Kaas, Michael M. Merzenich, H.P. Killackey, “The Reorganization of Somatosensory Cortex Following Peripheral Nerve Damage in Adult and Developing Mammals,” Annual Review of Neuroscience 6 (1983): 325-56.
[ii] Michael M. Merzenich, William M. Jenkins, Paul Johnston, Christoph Schreiner, Steven L. Miller, Paula Tallal, “Temporal Processing Deficits of Language-Learning Impaired Children Ameliorated by Training,” Science Vol. 271, Issue 5245 (1996):77-81.
[iii] Joe Verghese, Richard B. Lipton, Mindy J. Katz, Charles B. Hall, Carol A. Derby, Gail Kuslansky, Anne F. Ambrose, Martin Sliwinski, Herman Buschke, “Leisure Activities and the Risk of Dementia in the Elderly,” The New England Journal of Medicine Vol. 348 (2003): 2508-2516.
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