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

Brain damage frequently causes alterations in cognition that manifest in many different ways. The cognitive reserve, which protects us from these types of symptoms, is defined as the resistance of our mind to injury and deterioration.

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

• Related article: "Types of dementias: forms of loss of cognition"

Defining 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 to the central nervous system that would warrant a diagnosis of dementia, in the neuropsychological evaluation no cognitive affectation of the person with deterioration.

Once they start to develop neurodegenerative diseases, people with high cognitive reserve take longer to show symptoms than those with lower reserve. These effects have been related to the presence of greater cognitive abilities that make it possible to replace the behavioral and neuropsychological deficits typical of dementia.

However, in these cases usually symptoms come on suddenly, in contrast to the typical progression of this type of disease. This has been associated with the joint failure of the strategies used to deal with deterioration; After reaching a certain degree of brain damage, the person would be unable to put these compensatory abilities into action.

Unlike the term “brain reserve”, which emphasizes the resistance of the nervous system, cognitive reserve refers more to the optimization of brain resources through various strategies that allow 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 colleagues found that some people with the Alzheimer disease they did not show symptoms of dementia, or these were very mild compared to the neurological damage they presented. These people also had a greater number of neurons and their brains 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 increased number of neurons and synapses before disease development. Cognitive reserve is believed to depend on the degree of physical and mental stimulation of the person; for example, education and employment reduce the risk of dementia.

Twenty-five percent of older people in whom cognitive impairment is not detected before death meet the diagnostic criteria for 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 talked about in relation to dementia, in reality it can be applied to any alteration of brain functions; for example, increased reserve has been found to prevent cognitive manifestations of traumatic brain injury, 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 in cognitive reserve and, therefore, Therefore, they help 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

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

On the other hand, professions that are more cognitively stimulating are also highly beneficial. These effects have been detected above all in jobs that require a complex use of language, mathematics and reasoning, and are probably related to less 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 that studying mental stimulation. It is believed that aerobic exercise can improve cerebral blood flow, as well as the operation of the 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 function. Rodríguez-Álvarez and Sánchez-Rodríguez (2004) state that older people who do more leisure activities show a 38% reduction in the likelihood of developing dementia symptoms.

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

4. Bilingualism

According to research by Bialystok, Craik and Freedman (2007), people who use at least two languages ​​on a very regular basis During their lives, it takes an average of 4 years longer than monolinguals to present symptoms of dementia, once their mental health begins to deteriorate. brain.

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

Bibliographic references:

• Bialystok, E., Craik, E. YO. & 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.

• Rodríguez-Álvarez, M. & Sanchez-Rodriguez, J. L. (2004). Cognitive reserve and dementia. Annals of Psychology, 20: 175-186.

• Stern, Y. (2009). Cognitive Reserve. Neuropsychology, 47(10): 2015-2028.