Why does memory decline differ so much between people of the same age, even among closely-related individuals? How do some brains resist the damage caused by aging, injury, or dementing diseases more successfully than others? Researchers looking at imaging studies or autopsy results have tried to understand how one person with mild evidence of brain damage can be severely disabled while another with extensive brain changes shows only mild cognitive impairment.
Even among people who have sustained a head injury or a stroke, cognitive symptoms and cognitive recovery differ greatly. Some brains just seem to be stronger and more resilient in the face of aging or destructive events. "Cognitive reserve" is an important idea that sheds some light on this mystery.
What is Cognitive Reserve?
The main idea of "cognitive reserve" is that some brains keep on working more successfully than others despite similar degrees of destruction or degeneration, and that this is the effect of innate and acquired brain characteristics. At birth, our brains already differ. Some are larger, some smaller. Some have greater specific or general intellectual potentials. But lifetime experience, education, occupation, nutrition, and medical health all exert game-changing influences during our lives.
These differences are believed to reflect the quality of the brains’ internal connections and health. A healthy, well-developed, well-nourished brain, and a medically healthy body work more efficiently. It also resists the effects of injury from trauma or stroke, or compromise associated with diseases such as diabetes, high blood pressure, or depression.
The Positive Effects of a Stimulating Environment
During childhood, a cognitively stimulating environment promotes the development of larger brain volume. Physical exercise and cognitive stimulation increase molecules that enhance the brain’s ability to change continuously throughout an individual's lifetime. This is called brain plasticity. In addition, these molecules also promote the development of structures that permit nerve cells to pass an electrical or chemical signal to other nerve cells, called the synapse.
A healthy brain in a stimulating environment is growing new cells and making new connections. The combined effects of intellectual endowment, education, experience, and occupation appear important influences on how a damaged brain will compensate and preserve functioning. The decline in memory, executive function, and language skills associated with normal aging is slower in people with greater literacy.
In one important study, for example, people with low education and low lifetime occupational attainment were nearly three times as likely to develop dementia when compared to their better educated and more accomplished peers. Even when pursued later in life, engagement in cognitively-stimulating leisure activities has been demonstrated to increase resistance to clinical dementia. The theory of cognitive reserve has led researchers to discover that a more highly-trained brain is able to use its resources more efficiently and to recruit additional brain areas more readily when needed.
It may seem paradoxical, but the idea of cognitive reserve may also help us understand why dementia in more highly-educated people can progress more quickly once it becomes apparent. There may be a threshold of damage that even the most highly-developed brain cannot overcome. Though a brain with greater reserve fights off dementia's effects longer, exhaustion of the cognitive reserve typically leads to more rapid deterioration because the underlying destruction has already been more extensive than the clinical appearance would have suggested. Even among healthy older adults, memory decline develops later but then progresses more quickly in those with higher education.
Helpful Advice for Developing and Maintaining Brain Health
What advice was there for Andrew as he looked ahead to his later years? One of the most important things about the theory of cognitive reserve is that it gives us hope for fighting the effects of brain aging and degenerative disorders even though we have not yet been able to discover medications that cure dementia.
Early education, cognitive stimulation, and physical activity set the stage for later brain health. During adulthood, continued learning and engagement in challenging leisure-time activities can strengthen resistance to cognitive decline.
Brain health is further supported by physical activity and good self-care, which includes adequate sleep and stress-reduction, good nutrition, and care of medical health.
Individual genetic factors that affect risk for dementia are as yet unmodifiable, but the progression and expression of brain aging and disease are strongly affected by how we live and how we use our brains. Andrew, young enough to increase his physical and cognitive activities, is in a position to improve the long-term outlook for his cognitive health in later years.
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References and additional selected readings:
- Shin M, Sohn M, Lee J, et al. Effect of cognitive reserve on risk of cognitive impairment and recovery after stroke. The KOSCO study. Stroke 2020;51:99-1-7.
- Stern Y. Cognitive reserve. Neuropsychologia 2009;47(10):2015-28.
- Stern Y, Gurland B, Tatemichi TK, et al. Influence of education and occupation on the incidence of Alzheimer's disease. JAMA 1994 ;271:1004-1010
- Hall CB, Derby C, LeValley A, et al. Education delays accelerated decline on a memory test in persons who develop dementia. Neurology 2007;69:1657-64.
- Meng X, D'Arcy C. Education and dementia in the context of the cognitive reserve hypothesis: A systematic review with meta-analyses and qualitative analyses. PLoS ONE 2012;7(6):1-16.
- Xu H, Yang R, Qi X, et al. Association of lifespan cognitive reserve indicator with dementia risk in the presence of brain pathologies. JAMA Neurol 2019;76(10):1184-1191.
This content was last updated on: June 8, 2020
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