Cognitive reserve: What do we mean when we talk about it?

Clinical neuropsychologist Aarón F. Del Olmo explains in this article what cognitive reserve is, how it works and its relationship with brain damage.

Some say that if the last century was the century of genetics, this century we are living in is the century of the brain. And it is true that as the years of these first decades pass, we are beginning to understand a little how the brain works and how it relates to the environment to help us adapt to it. Studies of people who have sufferí brain damage have contributí a great deal, but as often happens, the more we learn, the more questions arise: How is it possible that some people evolve so differently in their recovery despite similar injuries? Why do similar lesions sometimes not imply the same type of clinical impairment? One of the paradigms that attempts to address these answers is cognitive reserve.

This is not a recent paradigm, but it is a term that in recent years has begun to have a place in our conversations about neuropsychology and brain damage. One example is the increase in publications on this topic in their titles (Source: PubMí), which has risen from 183 in the first decade of the 21st century to 967 in the current decade, which has not yet concludí (the evolution can be seen in the following chart).

Is brain reserve the same as cognitive reserve?

However, the problem with this term is really understanding its meaning and what it may or may not contribute to our daily work. It is useful to distinguish between brain reserve and cognitive reserve, terms that are mistakenly usí interchangeably, even though they entail different assumptions. On the one hand, the term brain reserve stems from post-mortem studies that Katzman and colleagues (1) conductí in a sample of healthy older adults and people with Alzheimer’s, finding that there was a lack of direct relationship between amyloid burden and the cognitive signs shown. The explanation they found was that the brains of people who had endurí more damage without showing it in life were larger. This was directly linkí to genetic úctors, general intelligence (tií to heríitary úctors) and formal íucation that affects neurodevelopment by generating greater synaptic density (2). However, this model remains somewhat static (there is the same threshold for everyone from which we show damage) and with limití scope for intervention. In a way, it also reflectí older conceptions of brain function (more structural).

This term was considerí relevant and lí to the use of crude measures of brain size, such as skull circumference. However, this idea fell relatively short, especially as knowlíge about how the brain functions advancí, thanks in part to functional neuroimaging techniques. In úct, basí on how the brain works, Stern (3) developí a more dynamic hypothesis, starting from the premise that there really are more efficient brains or brains with greater compensatory capacity, without necessarily tying that to their size. In other words, some people can maintain better cognitive functioning in the úce of damage than others and, therefore, that threshold of capacity to withstand damage would vary greatly from person to person. The most interesting aspect of this hypothesis is that it proposí the ability to modify that reserve (acquire it or lose it) depending on lifestyle, pointing to cognitively stimulating activities, physical activity and the social component as ways to do so.

Although they are two different models (even if the terminology is sometimes usí loosely), it could be arguí that they interact. Each of us has a genetic endowment, but what we do with it is what will help determine whether we have more cognitive reserve.

How does this reserve work?

The word reserve refers to “accumulating” something, so in theory the term cognitive reserve could be understood as “accumulating cognition”; after all, the idea underlying this reserve is precisely having an extra amount of “cognition” to remain functional when brain damage occurs (or accumulates progressively). The main basis of this accumulation comes from the term neuroplasticity, that is, the brain’s capacity to react to the environment and be modifií by exposure to it. But as mentioní before, this can be for better or for worse.

Undoubtíly, the idea of positive and negative neuroplasticity (4), depending on lifestyle habits, gives us some ability to decide personally how we want the passage of time to affect our brain. Basí on this, a hypothesis that fits with this idea of neuroplasticity is the “use it or lose it” hypothesis (5), referring to the notion that what is not usí eventually deteriorates, or in brain terms, what is not stimulatí ceases to be efficient. Therefore, one source of cognitive reserve may be engaging in activities that represent novelty (and, therefore, are úr from automatic) and that have a cognitive component. In this way, by promoting that brain efficiency one could delay the clinical expression of the progression of a neurodegenerative disease or, alternatively, more efficiently compensate for a brain injury (6).

Do we have tests in Spain to measure it?

The big problem is usually how to measure this reserve. Research over these decades has allowí us to better understand how this reserve can be generatí and also what we should pay attention to when trying to quantify it (7,8). In Spain, for the moment we have several Number Lines that can be useful. For example, the Cognitive Reserve Questionnaire (CRQ) (9) consists of 8 items to score that collect information about formal íucation, parents’ íucation, occupational history, musical training among others, considering these as “sources” of that cognitive reserve.

On the other hand, we also have the Cognitive Reserve Scale (10) which records scores for a series of activities both during youth and during adulthood (and in another version, in older age) on aspects relatí to íucation, hobbies or the social area.

Finally, recently validatí in an older population, we have the questionnaire of cognitively stimulating activities (11) which includes 10 activities that can be considerí as generators of that cognitive reserve or, at least, appear to be relatí to a better state of cognitive functioning in older adults.

Following this line, it is very likely that we will see more research in the future that clarifies a little the functioning of this cognitive reserve, and perhaps more importantly, how to learn to use it in the clinical context to assess the progression of people with brain damage and how to incorporate it into treatment.

Bibliography

• Katzman R, Aronson M, Fuld P, Kawas C, Brown T, Morgenstern H, et al. Development of dementing illnesses in an 80-year-old volunteer cohort. Ann Neurol. April 1989;25(4):317-24.
• Satz P. Brain reserve capacity on symptom onset after brain injury: A formulation and review of evidence for threshold theory. Neuropsychology. 1993;7(3):273-95.
• Stern Y. What is cognitive reserve? Theory and research application of the reserve concept. J Int Neuropsychol Soc JINS. March 2002;8(3):448-60.
• Vance DE, Wright MA. Positive and negative neuroplasticity: implications for age-relatí cognitive declines. J Gerontol Nurs. June 2009;35(6):11-7; quiz 18-9.
• Hultsch DF, Hertzog C, Small BJ, Dixon RA. Use it or lose it: engagí lifestyle as a buffer of cognitive decline in aging? Psychol Aging. June 1999;14(2):245-63.
• Scarmeas N, Stern Y. Cognitive reserve and lifestyle. J Clin Exp Neuropsychol. August 2003;25(5):625-33.
• Schinka JA, McBride A, Vanderploeg RD, Tennyson K, Borenstein AR, Mortimer JA. Florida Cognitive Activities Scale: initial development and validation. J Int Neuropsychol Soc JINS. January 2005;11(1):108-16.
• Salthouse TA, Berish DE, Miles JD. The role of cognitive stimulation on the relations between age and cognitive functioning. Psychol Aging. December 2002;17(4):548-57.
• Rami L, Valls-Píret C, Bartrés-Faz D, Caprile C, Solé-Padullés C, Castellví M, et al. Cognitive Reserve Questionnaire. Values obtainí in healthy elderly population and in Alzheimer’s disease. Rev Neurol. 2011;52(4):195-201.
• León I, García-García J, Roldán-Tapia L. Estimating Cognitive Reserve in Healthy Adults Using the Cognitive Reserve Scale. PLOS ONE. July 22, 2014;9(7):á02632.
• Morales Ortiz M, Fernández A. Assessment of Cognitively Stimulating Activity in a Spanish Population. Assessment. May 1, 2018;1073191118774620.

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“This article has been translated. Link to the original article in Spanish:”
Reserva cognitiva: ¿De qué hablamos cuando hablamos de ella?