katzman et al. (1998) conducted a study on the autopsy results of 10 people and found a pathology related to alzheimer's disease. however, the same patients showed no symptoms of alzheimer's disease during their life time. so, when pathology emerges in the brain, cognitive reserve helps to cope with cognitive decline. thus, individuals with high cognitive reserve cope better than those with low cognitive reserve even if they have the same pathology. this causes people with high cognitive reserve to go un-diagnosed until damage becomes severe. cognitive reserve, which can be estimated clinically, is affected by many variables. the cognitive reserve index questionnaire (criq) measures cognitive reserve under three main sources, namely the education, work activities and leisure time activities throughout the individual's lifespan. it is important to note that cognitive reserve (and the variables associated with it) do not "protect" from alzheimer's disease as a disease process—the definition of cognitive reserve is based exactly on the presence of disease pathology. this means that the traditional idea that education protects from alzheimer's disease is false, albeit that cognitive reserve is protective of the clinical manifestations of disease. as of 2010, there was insufficient evidence to recommend any way to increase cognitive reserve to prevent dementia or alzheimer's. on the other hand, cognitive reserve has a very important impact on neurodegenerative diseases. patients with high cognitive reserve showed a delay in cognitive decline when compared to patients with low cognitive reserve. however, when the symptoms of cognitive decline become symptomatic, patients with high cognitive reserve show rapid cognitive decline. the presence of cognitive reserve implies that people with greater reserve who already are suffering neuropathological changes in the brain will not be picked up by standard clinical cognitive testing. conversely anyone who has used these instruments clinically knows that they can yield false positives in people with very low reserve. from this point of view the concept of "adequate level of challenge" easily emerges. conceivably one could measure cognitive reserve and then offer specifically tailored tests that would pose enough level of challenge to accurately detect early cognitive impairment both in individuals with high and low reserve. this has implications for treatment and care. in people with high reserve, deterioration occurs rapidly once the threshold is reached. in these individuals and their careers early diagnosis might provide an opportunity to plan future care and to adjust to the diagnosis while they are still able to make decisions. a cognitive rehabilitation study, conducted with dementia patients, showed that patients with low cognitive reserve had better outcomes from cognitive training rehabilitation when compared to high cognitive reserve. this is due to the fact that the patients with high cognitive reserve had delayed cognitive symptoms and therefore the disease could no longer resist the pathology. furthermore, the improvement seen in the patients with low cognitive reserve indicates that these patients can build their cognitive reserve as a life-long process.