The model shows that even modest neuroprotective effects on basic cognitive units can lead to dramatic reductions in the number of AD's deterioration. From a functional viewpoint, normal cognition depends on the contribution of a number of basic cognitive units (BCU), which may represent neurons, synapses or cerebral circuits (biological units). The cognitive reserve refers to the number of BCU an individual has to lose before developing dementia symptoms. Consequently, reported incidence rates of AD's can be used to model and ‘visualize’ the effect of aging on BCU counts.
Mathematical model offers a unique method to estimate the effect of neuroprotection on AD incidence. Several observations support the model: 1) Virtually the entire population has AD-related pathology (amyloid plaques and neurofibrillary tangles) by age 90 years.
(p) of failure in cognition at any given age, age-specific z-scores can be directly obtained from these p values. Re-arranging the formula of the z-score, the following equation is obtained: E(y|x) = c−z-score×SD(y|x), where c represents the symptom threshold, E(y|x) is the expected BCU count (y) at any given age (x), and SD(y|x) is the corresponding standard deviation. Regression analyses of previous post-mortem analysis also suggest that SD(y|x) = 0.1 is the most likely value for the standard deviation. Consequently, the final equation is E(y|x) = BCU| age = 0.5−0.1×z-score. Results could only be obtained if such "hypothetical" neuroprotective treatment were universally applied to the general population.
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