Elsevier

The Lancet Neurology

Volume 11, Issue 11, November 2012, Pages 1006-1012
The Lancet Neurology

Personal View
Cognitive reserve in ageing and Alzheimer's disease

https://doi.org/10.1016/S1474-4422(12)70191-6Get rights and content

Summary

The concept of cognitive reserve provides an explanation for differences between individuals in susceptibility to age-related brain changes or pathology related to Alzheimer's disease, whereby some people can tolerate more of these changes than others and maintain function. Epidemiological studies suggest that lifelong experiences, including educational and occupational attainment, and leisure activities in later life, can increase this reserve. For example, the risk of developing Alzheimer's disease is reduced in individuals with higher educational or occupational attainment. Reserve can conveniently be divided into two types: brain reserve, which refers to differences in the brain structure that may increase tolerance to pathology, and cognitive reserve, which refers to differences between individuals in how tasks are performed that might enable some people to be more resilient to brain changes than others. Greater understanding of the concept of cognitive reserve could lead to interventions to slow cognitive ageing or reduce the risk of dementia.

Introduction

The possibility of a connection between life experience and the prevalence of dementia has long been discussed. In 1981, Gurland1 wrote “It is still an open matter whether there is an important sociocultural contribution to the prevalence of Alzheimer's and other forms of dementia occurring in the senium, but evidence now available is sufficiently intriguing to warrant further study of the issue”. Kittner and colleagues2 suggested that adjustment should be made for level of education when screening for dementia to avoid ascertainment bias, whereas Berkman3 suggested that we must remain open to the view that “educational level and/or socioeconomic behavior correlated with it may be a genuine risk factor for senile dementia and are worthy of scientific exploration in their own right”. Zhang and colleagues4 reported that a low level of education was associated with increased prevalence of Alzheimer's disease and dementia in a probability sample survey of 5055 older people not admitted to care facilities in Shanghai, China. These observations sparked my interest in studying the association between aspects of life experience and dementia; subsequently I have undertaken a long-term research programme to investigate cognitive reserve. In this Personal View I present a theoretical account of cognitive reserve, summarise epidemiological research that has lent support to the concept, and describe imaging studies that have attempted to identify the neural substrates of cognitive reserve. I will also discuss the potential clinical implications of the concept of cognitive reserve. Although I discuss cognitive reserve in the context of Alzheimer's disease and normal ageing, it has also been reported to provide benefit in patients with vascular injury,5, 6, 7 Parkinson's disease,8 traumatic brain injury,9 HIV,10 neuropsychiatric disorders,11 and multiple sclerosis.12

Section snippets

Brain reserve and cognitive reserve

The concept of reserve has been put forward to account for differences between individuals in susceptibility to age-related brain changes and pathology, such as that seen in Alzheimer's disease. Reserve is purported to act as a moderator between pathology and clinical outcome, thus accounting for the discontinuity. A convenient, although somewhat artificial, way to view cognitive reserve is to separate it into two main features: brain reserve and cognitive reserve.

The original concept of brain

Epidemiological evidence for cognitive reserve

My colleagues and I first investigated the concept of cognitive reserve in a study of incident dementia, based on the assumption that Alzheimer's disease pathology slowly develops over time independently of cognitive reserve, and that the pathology begins to accumulate many years before the onset of clinically diagnosed Alzheimer's disease (figure 1).23 Because people with greater reserve should be able to tolerate more Alzheimer's disease pathology, the onset of clinical dementia in these

Resting regional cerebral blood flow

Epidemiological studies suggest that at any given level of clinical severity in Alzheimer's disease, the degree of pathology will be greater in individuals with higher cognitive reserve than in those with lower cognitive reserve (figure 2). This idea was tested by assessment of resting regional cerebral blood flow as a surrogate for Alzheimer's disease pathology.30, 31 In patients matched for clinical severity, an inverse relation was found between resting regional cerebral blood flow and years

Application of cognitive reserve in clinical assessment

When cognition is assessed as part of a diagnostic work-up, the most appropriate validated indicators of cognitive reserve for each patient—such as educational or occupational attainment—should be used. In the event that an individual's level of education is not believed to be a good representation of his or her optimum cognitive functioning, assessment of IQ or consideration of occupation might be useful.

Individuals with high cognitive reserve, by definition, will present with disease-related

Cognitive reserve in remediation and prevention

Epidemiological evidence suggests that experiences at all stages, even in later life, can contribute to cognitive reserve. Intervention might, therefore, be useful even in elderly patients to impart or maintain reserve, slow age-related cognitive decline, and prolong healthy ageing. The most successful remediation approach so far has been aerobic exercise. Controlled studies have shown that in elderly individuals with respiratory capacity below the median at baseline, aerobic exercise increases

Conclusions

The concept of cognitive reserve arose from epidemiological observations. Various life exposures seem to be associated with resilience against age-related or pathology-related impairment of cognitive function. The original observations indicated the involvement of easily measurable variables, such as education or occupational attainment, but other lifestyle factors, for instance behaviours that stimulate cognition, personality, and so on, also seem to be important. Overall contributions to

Search strategy and selection criteria

This Personal View focuses primarily on the work of the author and his group since 1992. It does not represent an exhaustive literature review on this topic. Other included articles were already known to the author and are intended to support points made in the discussion.

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