The Cognitive reserve Is a system that tries to compensate for the losses and neuronal atrophies suffered that occur as the person grows older.
Cognitive reserve mechanisms work thanks to Neuronal plasticity And, thanks to them, the appearance of serious cognitive deficits can be delayed and, consequently, making our cognitive functions continue in correct operation thanks to the compensation.
What is cognitive reserve?
Cognitive reserve, also called cerebral reserve, is defined as the brain's ability to cope with brain damage caused by normal aging or disease.
In this way, the reserve would diminish the effects of this cerebral deterioration in the behavior, limiting the cognitive impact that this could provoke.
This concept arose to explain why some people with the same age and the same neuronal damages did not present the same cognitive deficits. Some of these people, with severe neural damage, characteristic of some neurological disease, did not even show symptoms of having any disease.
Therefore, it seems that there is no direct relationship between brain damage and symptoms, there is another variable that must be intervening.
One of the earliest studies attempting to demonstrate the existence of the reservation was carried out by Snowdon in 1997, a community of American nuns participated in this study and the results showed that the absence of cognitive deficits did not necessarily imply the absence of brain damage .
Since, in a brain analysis performed postmortem to one of the nuns, typical damages of the Alzheimer disease (Neurofibrillary tangles and senile plaques), however, this woman showed a correct cognitive performance until her death at age 101.
That is, although his brain was damaged, he did not show any symptoms of the disease, so the author concluded that there must be some mechanism to compensate for the cognitive decline that had to occur as a result of brain damage.
The reservation concept has changed a lot since the first time it was described. Currently the existence of two theoretical models for the study of the reserve is considered. The first model to be developed was the passive model, which talks about the cerebral reserve, focuses on studying anatomical characteristics of the brain (number of neurons, brain size...).
The second model most recently described, the active model, speaks of the cognitive reserve and understands that the reservation actively acts by recruiting and modifying the preexisting connections to overcome the connections lost by Brain damage .
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Passive model: cerebral reserve
According to this model the important thing is the anatomical potential of the brain (its size, the number of neurons and the density of the Synapses ). This potential would shape the person's brain reserve.
People who have more potential will have a greater reserve and tolerate better and longer brain damage before showing any cognitive deficit.
To understand it a little better, I will explain it by using Alzheimer's disease as an example and based on the following figure.
Image 1. Theoretical illustration of the reserve (Sampedro-Piquero & Begega, 2013).
Alzheimer's disease is neurodegenerative, which means that it progressively worsens over time. People with a greater brain reserve will start to notice Alzheimer's symptoms when the disease is more advanced and there is more brain damage, therefore, from the first onset of symptoms, the progression of the disease will be faster in the People with greater cognitive reserve.
Among the passive models we find the Threshold model (Satz, 1993), which revolves around the concept of Cerebral reserve capacity And supposes that there are individual differences in this capacity and that there is a critical threshold, after which the person would manifest clinical symptoms. It is governed by Three principles
- Increased cerebral reserve capacity acts as a protective factor.
- Lower cerebral reserve capacity acts as a vulnerability factor.
- Successive brain lesions have an additive character.
This model is usually studied with neuroimaging techniques, since in these can be observed if there are brain damages indicative of a disorder, although the person has not manifested symptoms.
The problem with this model is that it does not take into account the individual differences in cognitive processing, which is why Yaakov Stern developed another concept that took into account these factors: the active or cognitive reserve model.
Active model: cognitive reserve
According to this model, brain Is not a static entity but it would try to counteract the deterioration of the brain caused by aging or some disease.
The brain would alleviate these impairments thanks to its cognitive reserve which is described as the individual capacity to use cognitive processes and neuronal networks effectively, ie not only is it important that there are many connections, it is also vital that these connections are efficient .
Two mechanisms have been proposed through which our cognitive reserve would act:
- The neural reserve . This reservation refers to the preexisting cognitive strategies we use to cope with the demands of a given task. These strategies would translate into our brain in neural networks or specific forms of connection and would be flexible, so that they could adapt to brain damage and be less susceptible to it.
- Neural Compensation . This mechanism refers to our ability to use new neural networks to compensate for the impact that brain damage has had on other networks that previously functioned correctly to perform a given task. For this to happen brain plasticity is of vital importance.
Not all of us have the same neural reserve, it depends on multiple innate and environmental factors (eg type and level of education). The neural reserve is measured in terms of capacity and efficiency.
Capacity refers to the degree of activation of a specific network to perform a given task. The maximum capacity of a network would be shown when the difficulty of the task was so high that an increase of the difficulty would not increase the activation of the neural network, the neural network would have reached its maximum capacity. This point would be evidenced in the behavioral response of the person as it would decrease their effectiveness in the task.
There are times that effectiveness does not fall because other neural networks are recruited and these help the original network to perform the task. This phenomenon is more frequent in people with a greater cognitive reserve.
Efficiency refers to the ability to enhance a task with optimal performance using as few resources as possible. So if two people perform the same task optimally, the one with a greater cognitive reserve will use less resources for it than the one with the least reserve.
To summarize a little these models, which are not exclusive, I leave the following comparative table.
Reservation estimation
Given the importance of the reservation, the need to determine the cognitive reserve of patients before starting treatment or of people with a high probability of suffering from a neurological disorder, such as people with a family history, is evident. But how can we estimate a person's reservation?
Thanks to some studies, three types of techniques have been validated to measure the reserve:
- Clinical evaluations . These evaluations are done through tests or questionnaires and they measure variables such as education level, occupation, social and physical activities.
- Genetic studies . Some genetic factors have been associated with certain cognitive profiles.
- Neuroimaging studies . In them can be observed anatomical and functional characteristics of the brain that can serve as markers of the onset of some disease.
Variables that influence the reservation
At this point I guess you'll wonder how you can increase your booking. In this section I will expose the factures that can help you to increase it, therefore, it will not be spoken of innate variables if not acquired variables and, therefore, modifiable.
The following quotation illustrates very well what I want to convey in this section:
Education and premorbid intellectual quotient
Education is one of the variables that affects the most studied reserve. Many studies have shown that education is a protective factor for the onset of dementia and the cognitive deficits associated with aging.
In fact, low levels of education are considered a major risk factor for the development of neurodegenerative diseases such as Alzheimer's disease.
This variable is usually measured through clinical interviews and specific questionnaires such as Life Experiences Questionnaire (Questionnaire of Vital Experiences of M.J. Valenzuela) or the Cognitive Reserve Variable Questionnaire developed by Arenaza-Urquijo and Bartrés-Faz.
In addition to education, occupations are usually evaluated, measured through scales ranging from unskilled work to positions of high responsibility such as managers.
Often, both education and occupation depend on other variables such as the socioeconomic level, therefore, it is also necessary to investigate other factors that the individual can control to increase their cognitive reserve.
Another of the highly studied factors to evaluate to reserve is the IQ or IQ, standardized tests or questionnaires are used to measure it. Although CI has been proven to be highly heritable, it also depends on other acquired factors such as education and experience.
People with elevated IQ have been shown to have greater brain and cognitive reserve. These individuals present greater cerebral maturation during childhood and adolescence: greater cerebral size, cortical superspecializations and thinning of the dorsolateral prefrontal cortex.
But it seems that the assessment of IC with tests and questionnaires is more reliable to predict the development and cognitive decline of the person than the neuroimaging tests.
Cognitive and leisure activities
Activities that mentally stimulate us to read, write, play an instrument, and interact socially, have proved to be a protective factor against the development of dementias, even if they begin to occur when the person is already an adult.
Some studies have found that people who engage in this type of activity are 50% less likely to develop dementia. In addition, they protect the person against the decline of age, maintaining their cognitive performance for longer. Therefore, it is highly recommended to carry out this type of activities.
Physical activity
In addition to mental activity, physical activity Also seems to be important. Many studies suggest that physical activity is a potentially beneficial factor against the deterioration associated with old age and the development of dementias.
There are several mechanisms that could explain this effect, since physical exercise decreases some risk factors for dementias such as cardiovascular diseases And oxidative stress, also increases the production of trophic factors (maintenance and strengthening of neurons and their connections), neurogenesis (production of neurons) and functional plasticity.
These effects of the exercise have been proven with evidence of magnetic resonance . For example, one study compared two groups of older people, one group performed aerobic exercise routinely for 6 months and the other did not. In the first group we found an increase in brain volume, both of the white matter (connective material and Glial cells ) And gray (neurons).
Another study found that the effect of physical and social activities on protection against dementia and neural decline was similar to the effect of education. With this we can conclude that cognitive and physical stimulation are equally important.
So, as this famous quote tells us, the important thing is Mens sana in corpore sano.
If you want to know more about Lifestyles , Psychological aspects and risk factors that modulate the clinical presentation of Alzheimer's disease I recommend that you see the following documentary.
See the documentary: HBO: Documentaries: The Alzheimer's Project: Watch the Films: The Supplementary Series: Cognitive Reserve: What the Religious Orders Study is Revealing about Alzheimer's
References
- Arenaza-Urquijo, E., & Bartrés-Faz, D. (2014). Cognitive reserve. In D. Redolar, Cognitive Neuroscience (Pages 185-200). Madrid: Pan American Medical.
- Calero, M., & Navarro, E. (2006). Brain plasticity from the biological point of view. In M. Calero, & E. Navarro, Cognitive plasticity in old age. Evaluation and intervention techniques. (Pages 25-41). Barcelona: Octahedron.
- Castroviejo, P. (1996). Brain plasticity. Neurological Review , 1361-1366.
- Sampedro-Piquero, P., & Begega, A. (2013). Does physical and mental activity prevent cognitive impairment?: Evidence from animal research. Psychology Writings , 5-13. Doi: 10.5231 / psy.writ.2013.2607
- Snowdon, D. (s.f.). The Nun Study . Obtained from Alzheimer Association Monterrey.