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Cognitive reserve is an idea that was developed to explain why two people can suffer similar amounts of brain damage yet end up with different levels of brain function. Researchers have suggested that cognitive reserve may be greater in some people's brains than others, enabling them to overcome the damage caused by disorders such as strokes and Alzheimer's disease. Although researchers are not certain exactly how it arises, cognitive reserve could result from the brain working more efficiently than usual. An alternative mechanism could be that, if required, some people's brains are able to employ areas that are not normally used.
When researchers first noticed that the brains of two different people could have the same amount of neuropathological damage, yet one person would appear to function better than the other, a theory was developed concerning something called brain reserve. Brain reserve concerns the size of a person's brain before injury, and the theory is that the larger the brain and the more nerve cells available, the better a person can cope after brain damage. This theory does not take account the way in which an individual's brain works and its ability to adapt, so the cognitive reserve theory was developed.
The cognitive reserve hypothesis suggests that some people's brains are able to solve problems and process information more efficiently than others. Also, some may be able to use alternative parts of the brain, which are not normally used by most people, to perform certain tasks. Either or both of these factors could give people a reserve capacity in the brain, which comes into play when part of the brain is lost to injury or disease.
This could explain why, after death, certain people are found to have had brain changes associated with advanced Alzheimer's, yet they never showed symptoms of the disease while they were alive. Researchers think that Alzheimer's could appear later in people with a large cognitive reserve, even though their brains might show the same damage as those of people with a lower reserve, in whom the disease became obvious earlier. As people with a large cognitive reserve might be able to cope with relatively advanced Alzheimer's changes before losing brain function, this could mean that, when the disease is finally diagnosed, they may quickly go downhill.
Having a large cognitive reserve is associated with certain factors such as having a high IQ and taking part in a large number of interests and activities. It is thought that cognitive research could change throughout life, as a person's lifestyle changes. Those who continue to take up new activities and follow intellectual pursuits would tend to maintain a high reserve, while those who stopped using their brains might find their reserve diminishing.