What is cognitive reserve theory as it relates to Alzheimer's disease?
Cognitive reserve theory has been in the literature for some time, although our understanding of it has grown over the years. Cognitive reserve theory suggests that individual differences in brain health and cognition can have an effect on the expression and severity of Alzheimer's dementia. These findings are emerging in the literature and represent the best current wisdom on the idea of resilience.
The theory suggests that at any level of severity, an individual with higher preexisting cognitive capital could support greater levels of brain pathology without demonstrating the same debilitating deficits as someone with lower cognitive capital. This dates back to the 1980s when we were identifying Alzheimer's from autopsies. Researchers completed autopsies and identified individuals with no apparent symptoms of dementia who were found to have brain pathology consistent with advanced Alzheimer's disease. They theorized that these individuals had no apparent symptoms because they had a large enough cognitive reserve to offset the debilitating effects of the damage. It's not that the damage didn't occur, it's that their baseline was higher to compensate for the loss.
Besides post-mortem analysis, what else could support this theory and how has it progressed since that time? One particular study, with an N of 70 newly diagnosed individuals with Alzheimer’s disease, showed lower levels of beta-amyloid in individuals with higher levels of education. In their sample, 70 subjects had a lumbar puncture to examine their cerebral spinal fluid for the presence of both beta-amyloid and tau protein. The results of the study showed an inverse association, meaning when the years of education went up, the presence of beta-amyloid went down. There was no such relationship between education and tau. There was only a connection with the beta-amyloid.
These findings support the cognitive reserve theory in the first period of clinical evolution when Alzheimer's disease is first identified as MCI, mild cognitive impairment. However, that inverse relationship between education and tau disappears in the advanced phases of the disease. This means the individual may have more cognitive reserve in those initial phases, but once they progressed to later phases of Alzheimer's, individuals progressed at the same rate. So, they may have had a longer period upfront, but once that cascade began, the relationship disappeared as deficits increased.
To learn more about health promotion activities that can be used in individual, group, and community health settings across any adult/older adult population interested in building cognitive resilience, refer to SpeechPathology.com course, The Role of Resilience in Alzheimer's Dementia.