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The Puzzling Road to Fewer Alzheimer’s Patients: The Cognitive Reserve Hypothesis

In the IDA course "Dynamics of Individual Differences", students write a blog post on a topic of their interest that is related to an aspect that differs between individuals and changes across the lifespan. Enjoy reading the blog post of Anouk!

As I am sitting at my grandparents’ dining room table, my grandfather solves the newspapers’ daily crossword puzzle. ‘Doing these puzzles keeps his brain young’, my grandma says. It reminds me of an article I recently came across on my Facebook page. The headline read: ‘Study Finds Crossword Puzzles May Improve Memory Better Than Other Brain Games.’ My grandparents are relatively healthy 85-year-olds who live completely independent. Both socially and physically they live full lives with weekly golf- and Bridge games and regular visits with friends from all over the country. Cognitively, there are no noticeable problems. Why is that? Does my grandfather’s daily crossword puzzle have something to do with his retained cognitive abilities? Or does my grandparents’ busy weekly schedule keep them mentally sane? The cognitive reserve hypothesis suggests there could be something there.

First, let us dive into the aging of our brain for a little bit. Our brain contains about a 100 billion nerve cells called neurons. Each of those neurons is connected to many other neurons forming large networks of communication. Using electrical signals, messages are sent from neuron to neuron giving us the ability to think, remember, and learn. Most people are familiar with the fact that with age, changes take place in our body and brain. And as the body ages, it becomes more prone to developing diseases. Research has shown that in people over the age of 75, dementia is one of the most prevalent diseases (Marengoni et al., 2008). The most common form of dementia, that makes up 60-70% of cases, is Alzheimer’s disease (WHO, 2022). This disease, of which the symptoms include cognitive problems such as memory loss, confusion, and problems with speaking, is characterized by damage in the brain. It is believed that in Alzheimer’s disease the ability to send electrical signals from neuron to neuron is blocked. Scientists have yet to discover the exact way that Alzheimer’s develops, but most researchers agree that the accumulation of specific proteins in the brain (called beta-amyloid plaques and intracellular neurofibrillary tangles) probably results in problems in the brain’s communication system, leading to the various cognitive problems we see in Alzheimer’s disease (Wattamwar & Mathuranath, 2010). 

One of the difficulties with dementia, including Alzheimer’s disease, is that no cure is currently available. This lack of effective treatment combined with the overall aging of the population has led the World Health Organization (WHO) and Alzheimer’s Disease International to declare dementia a global public health priority (WHO, 2012). Besides ongoing efforts to develop effective treatment methods to combat Alzheimer’s disease, possibilities for prevention are widely explored as well. Research within this area has come up with important insights of how certain lifestyle factors can influence the chance of developing Alzheimer’s disease. Exercising regularly, refraining from smoking, and eating healthy throughout the lifespan have all shown to lower the risk of developing Alzheimer’s disease (Ko & Chye, 2020). 

But was my Facebook article right too? Should my grandparents and I solve crossword puzzles every day to lower our chances of developing Alzheimer’s disease?

Buffer for a broken brain

To evaluate the merit of activities like solving puzzles, we should first discuss some interesting differences observed between people in the symptoms resulting from Alzheimer’s related brain damage. As it turns out, there is no one-to-one relationship between the amount of damage in the brain and the severity of symptoms (Tucker & Stern, 2011). One study published in 1988 tracked the physical and cognitive health of 137 Swedish nursing home residents with yearly tests up until they passed away. After they passed away, their brains were examined. One thing the researchers did not expect to find was that ten of the elderly women with normal cognitive functioning, turned out to have severe Alzheimer’s related brain damage at autopsy (Katzman, 1988). In literature, many other similar examples demonstrating these individual differences can be found (Stern, 2002).

Based on these studies, scientists fostered the idea that people can have some sort of reserve against brain damage, which could explain these inconsistencies between the amount of damage and the severity of symptoms (Katzman et al., 1988). Generally, this reserve is split up into two categories: brain reserve and cognitive reserve. We speak of brain reserve when we talk about quantitative differences between people’s brains. Quantitative differences are things that we can directly measure and affect all people similarly, like the size of the brain and the number of neurons in it. As it turns out, when people have suffered similar amounts of brain damage, those with higher brain reserve tend to have fewer problems with cognitive functioning. Indeed, the brains of those ten cognitively fit women from the Swedish nursing home were full of Alzheimer’s related damage, which they could compensate with their bigger brains and higher number of neurons (Katzman et al., 1988).

But bigger is not always better. While the concept of brain reserve can explain a part of these individual differences, it is too simplistic to say that people with bigger brains will always have the biggest advantage (Stern, 2012). Additionally, how we use our brain reserve is of great importance too. This is where cognitive reserve comes in. If we would compare our brain to a computer, brain reserve would be the hardware, and cognitive reserve would be the software of our computer. With cognitive reserve, researchers refer to the amount of flexibility and efficiency with which people use their brain reserve (Stern, 2002). We can measure cognitive reserve by measuring factors that positively influence it like intelligence, level of education, work attainment, participation in recreational activities, and involvement in social relationships. The cognitive reserve hypothesis states that people with higher cognitive reserve will show higher cognitive performance at any level of Alzheimer’s related damage to the brain. This is even the case when we take the differences in brain reserve, like brain size and number of neurons, into account (Tucker & Stern, 2011). Numerous studies into the effect of brain damage on cognition provide support for the cognitive reserve hypothesis (Meng & D’Arcy, 2012).

A crossword a day keeps the doctor away…

If the way we use our brain is related to lower risks of showing signs of Alzheimer’s, could puzzles and games help us to lower our own risk on developing this disease? There are many Computerized Cognitive Training programs (or Brain-Training programs) that offer games to people who want to improve their cognitive abilities to lower their risk of developing Alzheimer’s. Scientists have not yet reached a consensus on the effect of games and puzzles on cognitive functioning and the risk of developing Alzheimer’s. In fact, there is a huge debate within the scientific community about this topic (Simons et al., 2016). This debate, although very interesting, is too extensive to go into in this blog. But if you do want to know more about the current status of this research, I would advise you to read this blog.

There are, however, studies that have specifically focused on the effects that crossword puzzles might have on cognitive functioning in elderly. Crossword puzzles are particularly interesting as a possible way to increase cognitive reserve because they are easily accessible to many people. In 2011, a study that followed elderly over multiple years concluded that crossword puzzle participation could delay the first signs of declining memory functioning by over two years (Pillai et al., 2011). Wow, that sounds promising. But wait! We should ask ourselves some questions when reading results like these. For example, aren’t people who solve the newspaper’s daily crossword puzzle very different from people who do not? Of course, they differ in their puzzle solving activities. But they might differ in other important ways too. For one, people who solve the newspaper’s daily crossword puzzle are all subscribed to the newspaper. This might seem like an unimportant detail, but it can in fact make a lot of difference. Why? People who are subscribed to a newspaper might on average be higher educated compared to people who are not. In turn, level of education has a positive influence on cognitive reserve. The difference that level of education makes is a fairly easy example, and the authors of this study did take it into account, but there could be many more ways in which the group of crossword puzzlers might differ from other people.

More recently, researchers compared the effect of Computerized Cognitive Training games to the effect of crossword puzzles on mild cognitive decline. The authors of this study did not rely on people who already had a subscription to the newspaper and did the crossword puzzle. They randomly assigned people to two groups: a group that had to solve crossword puzzles and a group that had to enroll in Computerized Cognitive Training. This study, of which the conclusion reached my Facebook page, showed that crossword puzzles were more effective in protecting against cognitive decline as opposed to Computerized Cognitive Training (Devanand et al., 2022). Using this random assignment to two different groups gives us some more confidence that crossword puzzles might have merit. However, before doctors start advising everyone to start doing crossword puzzles to prevent Alzheimer’s, it is probably best to wait if other researchers find similar results.

Steering the brain away from Alzheimer’s

In conclusion, higher cognitive reserve is associated with higher cognitive functioning and a lowered risk for Alzheimer’s related symptoms. Research suggests that we could be able to increase our own cognitive reserve by participating in recreational activities and retaining close social relationships.

Will my grandfather’s efforts to solve the daily crossword puzzle help him increase his cognitive reserve? Maybe. When it comes to brain training programs, some scientists have warned us not to get our hopes up. However, some studies looking specifically into crossword puzzles have provided some promising results. These studies are limited in number, however, so we should remain cautious when drawing conclusions. For now, I will advise my grandfather to keep on solving his puzzles, because if it makes him happy, there is certainly no harm done. And who knows, maybe it will help his brain a little bit too.

If you are interested in reading the articles mentioned in this post, references and links are provided here:

Devanand, D. P., Goldberg, T. E., Qian, M., Rushia, S. N., Sneed, J. R., Andrews, H. F., Nino, I., Phillips, J., Pence, S. T., Linares, A. R., Hellegers, C. A., Michael, A. M., Kerner, N. A., Petrella, J. R., & Doraiswamy, P. M. (2022). Computerized games versus crosswords training in mild cognitive impairment. NEJM Evidence, 1(12).

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), 138-144.

Ko, Y., & Chye, S. M. (2020). Lifestyle intervention to prevent Alzheimer’s disease. Reviews in the Neurosciences, 31(8), 817-824.

Marengoni, A., Winblad, B., Karp, A., & Fratiglioni, L. (2008). Prevalence of chronic diseases and multimorbidity among the elderly population in sweden. American Journal of Public Health, 98(7), 1198-1200.

Meng, X., & D’Arcy, C. (2012). Education and dementia in the context of the cognitive reserve hypothesis: A systematic review with meta-analyses and qualitative Analyses. Plos One, 7(6).

Pillai, J. A., Hall, C. B., Dickson, D. W., Buschke, H., Lipton, R. B., & Verghese, J. (2011). Association of crossword puzzle participation with memory decline in persons who develop dementia. Journal of the International Neuropsychological Society, 17(6), 1006-1013.

Simons, D. J., Boot, W. R., Charness, N., Gathercole, S. E., Chabris, C. F., Hambrick, D. Z., & Stine-Morrow, E. A. L. (2016). Do “Brain-Training” programs work? Psychological Science in the Public Interest, 17(3), 103-186.

Stern, Y. (2002). What is cognitive reserve? Theory and research application of the reserve concept. J Int Neuropsychol Soc, 8(3), 448-460.

Stern, Y. (2012). Cognitive reserve in ageing and Alzheimer’s disease. The Lancet Neurology, 11(11), 1006-1012.

Tucker, A. M., & Stern, Y. (2011). Cognitive reserve in aging. Current Alzheimer Research, 8(4), 354-360.

Wattamwar, P. R., & Mathuranath, P. S. (2010). An overview of biomarkers in Alzheimers disease. Annals of Indian Academy of Neurology, 13, 116-123.

Weg, A. (2022). Study finds crossword puzzles may improve memory better than other brain games.

World Health Organization. (2012). Dementia: A public health priority (ISBN: 978 92 4 156445 8). WHO Press.

World Health Organization. (2022). Dementia. WHO Press.

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