Scientists once thought that the brain stopped developing after the first few years of life. They thought that connections formed between the brain’s nerve cells during an early “critical period” and then were fixed in place as we age. If connections between neurons developed only during the first few years of life, then only young brains would be “plastic” and thus able to form new connections. (To learn more about neurons, click here.) Because of this belief, scientists also thought that if a particular area of the adult brain was damaged, the nerve cells could not form new connections or regenerate, and the functions controlled by that area of the brain would be permanently lost. However, new research on animals and humans has overturned this mistaken old view: today we recognize that the brain continues to reorganize itself by forming new neural connections throughout life. This phenomenon, called neuroplasticity, allows the neurons in the brain to compensate for injury and adjust their activity in response to new situations or changes in their environment.
How does neuroplasticity work? A large amount of research focuses on this question. Scientists are certain that the brain continually adjusts and reorganizes. In fact, while studying monkeys, they found that the neuronal connections in many brain regions appear to be organized differently each time they are examined! While it remains uncertain at this writing (April 2003) whether reorganization in the adult brain involves the formation of new neural connections, existing neural pathways that are inactive or used for other purposes do show the ability to take over and carry out functions lost to degeneration. Understanding the brain's ability to dynamically reorganize itself helps scientists understand how patients sometimes recover brain functions damaged by injury or disease.
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