Cognitive reserve: what it is and how it protects us from dementia

March 29, 2024

Brain damage often causes alterations in cognition that manifest themselves in very different ways. The cognitive reserve, which protects us from this type of symptoms , is defined as the resistance of our mind to injuries and deterioration.

In this article we will examine the concept of cognitive reserve, particularly in the framework in which it is most commonly used: dementia. We will also describe the factors that influence the presence of a greater cognitive reserve and the preservation of memory .

Related article: "Types of dementia: forms of cognition loss"

Defining the cognitive reserve

The concept "cognitive reserve" is used to refer to the ability to resist brain deterioration without presenting symptoms. Sometimes, even if there is objective damage in the central nervous system that would justify a diagnosis of dementia, in the neuropsychological evaluation no cognitive impairment of the person with deterioration is detected.

Once they begin to develop neurodegenerative diseases, people with a high cognitive reserve take longer to show symptoms than those with a lower reserve. These effects have been related to the presence of greater cognitive abilities that allow supplement the behavioral and neuropsychological deficits of dementia.

However, in these cases usually the symptoms appear abruptly , in contrast to the typical progression of this type of diseases. This has been associated with the joint failure of the strategies used to deal with the deterioration; Once a certain degree of brain damage has been achieved, the person will be unable to activate these compensatory skills.

Unlike the term "brain reserve", which emphasizes the resistance of the nervous system, the cognitive reserve refers rather to the optimization of brain resources through different strategies that allow the performance to decrease to a lesser extent in the presence of neurological damage. Thus, it is a functional concept, not just a structural one.

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Cognitive reserve and dementia

In a 1988 study, Katzman and his collaborators found that some people with Alzheimer disease they did not show symptoms of dementia, or they were very mild compared to the neurological damage they presented. These people also had a greater number of neurons and their brain weighed more than expected.

The results of this and other studies have been attributed to the existence of a cognitive reserve, that is, of a greater number of neurons and synapses before the development of the disease . It is believed that the cognitive reserve depends on the degree of physical and mental stimulation of the person; for example, education and employment reduce the risk of dementia.

The 25% of elderly people in whom no cognitive impairment is detected before their death meet the diagnostic criteria of Alzheimer's disease (Ince, 2001). In this way, even if someone presents a clinical picture of dementia at the neuroanatomical level, if their cognitive reserve is high, it is possible that the symptoms do not manifest themselves.

Although cognitive reserve is usually discussed in relation to dementia, it can actually be applied to any alteration of brain functions; for example, it has been found that a greater reserve prevents the cognitive manifestations of traumatic brain injuries, schizophrenia, bipolar disorder or depression .

Related article: "Alzheimer's: causes, symptoms, treatment and prevention"

Factors that prevent deterioration

There are different types of factors that contribute to the increase of cognitive reserve and, therefore, help to prevent the psychological symptoms of dementia and other disorders that affect the brain.

As we will see, these variables are fundamentally related to the level of activity and stimulation, both physically and mentally .

1. Cognitive stimulation

Several studies have found that continuous cognitive stimulation increases brain cognitive reserve. A very important factor in this regard is the educational level, which is associated with greater connectivity and neuronal growth throughout life, but especially at early ages.

On the other hand, professions that are more stimulating at the cognitive level are also very beneficial. These effects have been detected especially in jobs that require a complex use of language, mathematics and reasoning , and probably are related to a lower atrophy in the hippocampus, a structure involved in memory.

2. Physical activity

Research on the influence of physical activity on cognitive reserve is less conclusive than research on mental stimulation. It is believed that Aerobic exercise can improve cerebral blood flow , as well as the functioning of neurotransmitters and the growth of neurons.

3. Leisure and free time

This factor is related to the previous two, as well as to social interaction, which also stimulates brain functioning. Rodríguez-Álvarez and Sánchez-Rodríguez (2004) affirm that elderly people who perform more leisure activities show a 38% reduction in the likelihood of developing dementia symptoms .

However, correlational investigations carry a risk of reversal of causality; thus, it could simply happen that people with less cognitive impairment are involved in more leisure activities, and not that they prevent the progression of dementia.

4. Bilingualism

According to research by Bialystok, Craik and Freedman (2007), people who use at least two languages in a very normal way during their lives take an average of 4 years more than monolinguals to present symptoms of dementia, once the encephalon starts to deteriorate .

The hypothesis proposed by these authors is that competition between languages favors development of an attention control mechanism . This would not only explain the benefits of bilingualism for the cognitive reserve, but also the improvement in the cognitive functioning of children and adults who master several languages.

Bibliographic references:

Bialystok, E., Craik, E. I. & Freedman, M. (2007). Bilingualism as a protection against the onset of symptoms of dementia. Neuropsychology, 45: 459-464.

Ince, P. G (2001). Pathological correlates of late-onset dementia in a multicenter community-based population in England and Wales. Lancet, 357: 169-175.

Katzman, R., Terry, R., DeTeresa, R., Brown, T., Davies, P., Fuld, P., Renbing, X. & Peck, A. (1988). Clinical, pathological, and neurochemical changes in dementia: a subgroup with preserved mental status and numerous neocortical plaques. Annals of Neurology, 23 (2): 138-44.