Cognitive reserve is a little-known concept, but it is essential to protect our brain and maintain our well-being. In fact, did you know that more than 25% of elderly people meet the pathological criteria to be diagnosed with Alzheimer’s disease, but do not show signs of cognitive decline in their daily lives? How is it possible? The answer lies precisely in cognitive reserve.
The research that discovered the existence of cognitive reserve
In 1988, neuroscientist Robert Katzman of the University of California analyzed the brains of 137 people with an average age of 85, most of whom had been diagnosed with dementia while they were alive. After performing the post-mortem examination, he discovered that there were 10 people who showed the same brain lesions as those who suffered from Alzheimer’s. However, their relatives confirmed that they showed no signs of the disease while they were alive.
That discovery marked a before and after in the understanding of the brain. He revealed that, even if two people present similar brain alterations, one may present symptoms of the disease and another may not.
Katzman also noted that people who had pathological signs of the disease at the brain level (visible physiological lesions), but did not present symptoms and had maintained normal cognitive functioning, had larger brain sizes. This suggests that they probably had a higher neuronal density.
The neuroscientist also proposed that a larger cranial size could be a favorable factor that protects people from developing the clinical symptoms of a neurodegenerative disease. Later studies confirmed that approximately 25% of very old people meet the pathological criteria for Alzheimer’s, but do not show signs of the disease.
He called this ability to tolerate a greater degree of the disease brain reserve.
What is cognitive reserve exactly?
Cognitive reserve, as it is also known, is the ability to cope with the brain changes caused by normal aging or a neuropathological process without suffering major clinical symptoms. In other words, it contributes to limiting the impact of brain injuries and their manifestations on daily life, largely preserving normal cognitive functioning.
This capacity is not limited only to the morphological characteristics of the brain, but also includes the ability to perform cognitive tasks efficiently. Therefore, it is a sign of great brain plasticity. In practice, the person is capable of recruiting alternative neural networks to continue carrying out their activities with a certain normality.
The 2 pillars on which the brain reserve is based
At first, neuroscientists were inclined to think that brain reserve was due to anatomical potential. That is, it depended on the physiological characteristics of the brain, such as the greater number of neurons or the greater synaptic density. According to this model, a brain with more neurons or synapses would have an advantage because these characteristics would help it maintain normal functioning even in the face of injuries.
Over the years, new research has begun to outline an active model in which the person plays a more leading role. From this perspective, the brain itself tries to actively counteract the changes typical of aging or injury.
In order to compensate for these structural deficiencies, the brain optimizes its networks to process information more efficiently. In fact, our brain has some very powerful cards up its sleeve that it can resort to in these circumstances:
1. Neural reserve: it is the ability to use pre-existing cognitive strategies to face challenges. It means that the neural networks used are more efficient and flexible, so they are also less vulnerable to brain damage.
2. Neural compensation: it is the ability to use new neural networks aimed at compensating for those that we often used. It allows us to deal with day-to-day tasks in a similar way by establishing alternative neural pathways to those that have been affected or damaged.
In practice, every time we perform a cognitive task of normal difficulty, such as reading or solving a problem, a specific neural network in the brain is activated. That default network helps us deal with the task more efficiently.
However, thanks to neural reserve and compensation processes, our brain is able to reconstruct these damaged networks and even create different paths to achieve similar functioning.
In fact, cognitive reserve becomes more evident when the complexity of the task increases, as can be seen in the graph below. Greater cognitive reserve will help us function better for longer, especially when we have to deal with unexpected life events that challenge our conventional psychological resources.
How does cognitive reserve vary over the years?
Cognitive reserve is an unstable construct that changes. Regardless of the intrinsic plasticity of the nervous system, this usually decreases over the years, although it is maintained throughout life.
In fact, research has shown that cognitive reserve is a dynamic capacity of the brain that is maintained throughout life. However, it changes over time, depending largely on our habits.
It must also be taken into account that cognitive reserve is not a magic shield. People who have a high cognitive reserve are not exempt from suffering the symptoms of neurodegenerative diseases, but will manifest them years later.
These people reach the turning point when the brain damage is more severe and they begin to present signs at a delayed rate, compared to those who have a low cognitive reserve, as can be seen in the following graph.
How to increase cognitive reserve?
Beyond the innate characteristics of the brain and genetic variables, which are not modifiable, there are other aspects that we can influence to develop cognitive reserve. As Santiago Ramón y Cajal said, “Every man can be, if he sets his mind to it, the sculptor of his own brain.”
It is known that education is an essential pillar of cognitive reserve since it plays a protective role in the brain. It has also been proven that cognitively stimulating leisure activities reduce the risk of developing neurodegenerative diseases.
In different studies it has been found that high levels of mental activity reduce the risk of developing dementia by up to 50%. Therefore, there is no doubt that intellectual activities are essential to maintain cognitive functioning and protect the brain from decline. And we must not forget leisure activities. Distracting ourselves and spending quality time with other people reduces the risk of developing dementia by 38%, according to research carried out at the universities of Salamanca and Santiago de Compostela.
Learning new things at all stages of life is also particularly important for increasing cognitive reserve. In this way we continually generate new synaptic connections that maintain brain plasticity. In this sense, a study carried out at University College London found that people who continue learning throughout their lives are more likely to develop their cognitive reserves.
Anything goes, as long as it represents a challenge, from playing a new sport to learning a new language. In fact, research carried out at the University of York with 184 patients diagnosed with dementia, 51% of whom were bilingual, revealed that they showed symptoms 4.1 years later than those who only spoke one language.
It is also very convenient to change routines or introduce new elements into our lives. Routines are important to lead an organized life and reduce stress, especially in the elderly. However, automating tasks also decreases brain activation. For this reason, breaking habits from time to time or setting new goals implies a stimulus that promotes brain activation. In other words, it allows us to keep the brain active.
Last but not least, it has been appreciated that physical exercise also plays a protective role for the nervous system. It reduces the atrophy that usually occurs in the brain over the years and improves its functional plasticity. Physical activity promotes an increase in gray and white matter, in addition to promoting the growth of new neurons in the hippocampus, an essential structure for memory.
Exercising reduces inflammation, also at the brain level, in addition to increasing the production of trophic factors and neurogenesis. Physical exercise improves cerebral blood flow, which guarantees a greater supply of oxygen and nutrients to the brain for it to function better.
In summary, social activities such as physical exercise and intellectual challenges increase cognitive reserve because they promote neuroplasticity and resistance to neuronal death. Therefore, if we want to protect our brain, we must make sure we stay active, physically and mentally.
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