The idea that cognitive reserve (CR) or brain reserve capacity can be neuroprotective against dementia has been discussed for approximately 2 decades. A new metastudy in PLoS highlights the positive and negative aspects and confirms the CR theory.
Cognitive reserve or brain reserve capacity explains why individuals with higher IQ, education, or occupational attainment have lower risks of developing dementia, Alzheimer’s disease (AD) or vascular dementia (VaD). The CR hypothesis postulates that CR reduces the prevalence and incidence of AD or VaD.
CR also explains the relationship between education, occupational complexity, reading ability, IQ and dementia. This reserve is seen to be a result of changes in the brain itself, resulting from changes in brain structure and processing. Morphological and neurochemical brain changes have been observed in animals raised in stimulating environments. CR can take two forms: (1) neural reserve in which existing brain networks are more efficient, or have greater capacity, may be less susceptible to disruption; and, (2) neural compensation in which alternate networks may compensate for the pathological disruption of preexisting networks.
In this study, education was used as a proxy measure of CR. Researchers explored the evidence linking education and dementia. The CR hypothesis postulates that higher education:
- reduces the prevalence of dementia;
- reduces the incidence of dementia;
- has no affect on the age of onset of dementia;
- results in an accelerated cognitive decline – as a result of a threshold effect;
- has no effect on the age of death;
- leads to a higher level of clinical performance on initial assessment;
- shows greater brain pathology in postmortem and imaging studies among those with dementia.
The results demonstrated that there is robust evidence that a high level education in early life is related with a significant reduction both in the prevalence and incidence of dementia, including AD and VaD. These results are in accordance with the CR hypothesis, which assumes some aspects of life experience such as education protects against the onset of dementia. Education also influences the course and outcome of the disease in terms the pattern of cognitive decline and underlying brain pathology.
The study also found that adult-life work complexity, social network and complex leisure activities also reduce the occurrence of dementia complements the evidence presented in this systematic review. It is notable that both prevalence and incidence studies showed positive evidence that high education is a protective factor of against dementia. Low education is not merely a risk factor for dementia, but is a contributory factor in the development of dementia. The findings of this systematic review support the general tenets of the cognitive reserve hypothesis
The downside of CR is that implicit in the literature is the idea that cognitive reserve will limit the clinical expression of the underlying disease until a threshold level of brain pathology is reached at which point the CR can no longer compensate for the underlying physical brain degeneration. Thus the relationship between CR and dementia will differ depending on the underlying pathology. Implicit is the possibility that directly enhancing CR may help forestall the clinical manifestation of AD and dementia.