PLASTICITY [ back to Glossary Index ]
Plasticity is the physical capacity of the brain to reorganize itself following injury by trauma, stroke or other causes. While nerve cells which are killed cannot regenerate, nearby nerve cells can grow new dendrites, new dendritic spines and/or new axonal boutons to form new synapses that replace, to some extent, the synapses that were lost. This process is imperfect and can be impeded by scar formation. It proceeds best in very young children, at a time when nerve cells and their connections are are still in the early phase of rapid development, and when chemical nerve growth factors circulating in the brain are most plentiful. A child who loses the left side of his brain from a tumor at age 2, can grow up with normal language function, because the neurons in his right hemisphere take on the language function. Neuronal plasticity progressively declines with age. The lack of plasticity becomes a subtle factor in slowing recovery from a TBI when people reach their 40s, and can be a strong, obvious factor in blocking recovery for a person who suffers a TBI at age 75 or 80. Behavioral plasticity is the ability to alter one's behavior to adapt to injury. Even if a person with an anoxic brain injury cannot regrow hippocampal neurons, he may learn to encode and retrieve new information with the use of a tape recorder, Palm Pilot or day planner; and in this way compensate for lost memory function by externalizing his memory. Further if the loss of memory is severe in one way area, but mild in others, the person can learn to retrieve memories through different conceptual routes. Thus someone who can no longer remember colors of things, can retrieve them through increased attention to their sizes, shapes, textures, and the like.