Use it or lose it: How a lifetime of challenging our brains may slow the onset of dementia symptoms

June 23rd, 2026

Written by Catrina Hacker

Most of us know an older adult living with dementia. In the United States, about one in nine adults aged 65 or older has Alzheimer’s disease, one of the most common forms of age-related dementia¹. To meet this challenge, in addition to doing research aimed at developing treatments, many researchers are also trying to understand what lifestyle choices might help protect us from experiencing symptoms of dementia as we age. One popular idea, called the cognitive reserve hypothesis, argues that a key factor is keeping our minds active. In this post I’ll explain what the cognitive reserve hypothesis is and unpack the evidence to support it.

The origins of the cognitive reserve hypothesis

The cognitive reserve hypothesis was developed to solve a mystery. Dementia is associated with slow brain changes that worsen over many years, referred to as its pathology³. Historically, researchers could only study Alzheimer’s pathology when patients donated their brains to science after death. The researchers could then compare how much pathology they observed in each patient’s brain with the symptoms documented by doctors during a patient’s life, like memory loss, inability to maintain attention, or difficulty reasoning². However, over time, researchers noticed something puzzling about these studies: the amount of pathology measured in a patient’s brain didn’t always predict how severe their symptoms were during their lives. Some patients had clear Alzheimer’s brain pathology but reported weak or no symptoms^4,5, leaving researchers puzzled as to why the degree of Alzheimer’s brain pathology did not predict the severity of a patient’s symptoms.

One hint came from a now-famous “Nun Study” that began in the 1980s. In this study, an epidemiologist followed a cohort of Catholic nuns who consented to annual neuropsychological testing and to have their brains studied after death. One particularly interesting data point came from autobiographical essays the nuns had written much earlier in their lives as part of their training⁶. The researchers focused on two features of the autobiographies: idea density, the number of ideas expressed in each essay, and grammatical complexity, how sophisticated each sentence was. They found that nuns whose autobiographical essays had higher idea density and grammatical complexity early in life were less likely to develop symptoms of dementia later in life. In one notable case, Sister Mary, an avid reader who was heavily engaged in her community, died at the age of 101 with typical cognitive ability despite clearly showing brain pathology associated with Alzheimer’s disease when her brain was examined after her death⁷.

These observations led many to speculate that people who use their brains more actively throughout their lives may be more robust to dementia-related brain changes, leading to fewer symptoms. The cognitive reserve hypothesis formalizes these ideas by making a distinction between when a patient’s brain begins to show the physical changes associated with dementia and when a patient reports experiencing symptoms. According to the hypothesis, challenging our brains throughout our lives through things like reading, learning about new things, solving complex problems at work, or engaging in rich social interactions, builds up a cognitive reserve that makes our brains more flexible and able to adapt to slow and persistent dementia-related brain changes⁵. The more we exercise and apply our brains to a variety of complex problems, the more adaptable our brains become, building up a bigger cognitive reserve. The bigger a patient’s cognitive reserve, the more disease progression they will experience in brain pathology before they begin to show symptoms. In other words, cognitive reserve delays and slows the onset of symptoms after physical dementia-related brain changes begin.

The brain changes that underlie cognitive reserve

The cognitive reserve hypothesis makes a surprising and counterintuitive prediction: an individual with higher cognitive reserve will show more brain pathology for the same severity of disease symptoms than someone with lower cognitive reserve. This is because their cognitive reserve can compensate for and thereby protect them from the effects of low levels of disease-related brain change. To demonstrate this directly, one group of researchers developed a way to approximate the degree of brain pathology in living patients by measuring the rate of blood flow to parts of the brain that are typically damaged by dementia⁸. They reasoned that weaker blood flow means more brain damage and thus stronger brain pathology. Consistent with the counterintuitive prediction made by the cognitive reserve hypothesis, they found that for similar levels of symptom severity patients with higher education levels had weaker blood flow in dementia-associated brain regions, suggesting stronger pathology. Further work found that the same trend was true when considering how complex and demanding an individual’s occupation was. Patients whose jobs required them to solve complicated problems and manage complex interpersonal relationships  had weaker blood flow in dementia-associated areas than those with less complex occupations, even after accounting for differences in level of education⁹. Since occupation typically occurs after education and spans most of a person’s lifetime, this suggests that it is truly a lifetime of experience that shapes an individual’s cognitive reserve.

If brain pathology needs to be stronger to produce the same symptoms in a patient with high cognitive reserve, then what other brain changes compensated for those related to the disease? The answer may lie in changes to the complicated web of connections between different parts of the brain called brain networks. People who have high cognitive reserve are thought to have more flexible brain networks that allow them to utilize a different connection to accomplish the same task when the one they usually use starts to break down¹⁰. To make sense of this, you can think about different brain areas like airports and the connections between them like flights. If you want to get from Philadelphia to Phoenix you might book a connection through Houston. However, if Houston airport stopped offering flights or the flight from Philadelphia to Houston was no longer available from your favorite carrier, you could still get to Phoenix by connecting through another city or using a different airline carrier who still flies to Houston. Dementia’s impact on the brain is like removing airports and flights from the list of possibilities. Individuals with higher cognitive reserve start with more options before the damage begins, so they are better able to compensate when a single flight or airport is removed from the map. Therefore, the damage has to be more extensive before a patient can no longer compensate for those changes.

Several recent studies have been able to test this directly using a modern method of measuring brain activity in living patients capable of capturing how connected different brain areas are to one another. One study found that patients with higher cognitive reserve had stronger connections between a part of the brain that is not typically impacted in early stages of dementia, called the frontal cortex, and other parts of the brain¹¹. Therefore, cognitive reserve may increase connections with frontal cortex, thereby allowing patients to utilize these numerous connections to compensate for and replace damaged connections in other parts of the brain impacted by dementia. Another study identified a whole network of brain regions, including parts of frontal cortex, that tended to be more strongly connected to one another in healthy adults with higher cognitive reserve¹². This further suggests that experience shapes brain networks that may be capable of compensating for slowly accumulating dementia-related damage.

Challenges to the cognitive reserve hypothesis

While there is ample support for the cognitive reserve hypothesis, there are several challenges to the interpretation of these findings worth noting. Experiments on cognitive reserve require scientists to gain measurements of both disease pathology and cognitive reserve. However, both pathology and cognitive reserve are difficult to measure directly¹³. For example, the study mentioned above that looked for brain networks associated with stronger cognitive reserve used IQ as a proxy for cognitive reserve. However, IQ itself is influenced by many other factors, like childhood environment and socioeconomic status, that may instead be responsible for the differences observed in the study. So, while IQ may be associated with these brain changes, it’s hard to say exactly what causes the brain changes.

Another challenge is that when it comes to measuring the impact of lifestyle on brain activity it is difficult to say whether any one factor causes the observed differences over others, since there are so many potentially influential factors at play¹⁴. Scientists get around this in the lab by looking at the impact of changing only one factor at a time while keeping all other factors the same. This allows them to say that the factor being changed has a given impact, since it is the only thing changing in the experiment. However, it is impossible to change only one factor at a time when considering a lifetime of experience for a group of patients. Therefore, it is difficult to say with certainty that any particular lifestyle choice can cause a positive or negative change in brain activity. This is partly why the Nun Study is so popular. Many nuns joined the convent early in their lives and lived very similar lifestyles in terms of factors like nutrition and environment. So, while still not as carefully designed as a lab study, there are shared environmental factors that make the Nun Study more like a lab experiment than most other studies looking at lifestyle.

Despite these challenges, research on cognitive reserve offers a promising window into what lifestyle choices and brain changes may help protect older individuals from the impact of dementia. These insights might in turn provide entry points toward developing new therapies to prevent or delay the onset of dementia. Beyond dementia, many of the behaviors associated with higher cognitive reserve, such as rich social interactions, are already known to be beneficial in supporting the health and mental well-being of individuals throughout their lifetimes. So, while diet and exercise tend to get most of the attention, cognitive reserve suggests how challenging your brain can be an equally important part of a happy and healthy lifetime.

References

1. 2026 Alzheimer’s disease facts and figures. Alzheimers Dement. 22, e71345 (2026).
2. CDC. Signs and Symptoms of Dementia. Alzheimer’s Disease and Dementia https://www.cdc.gov/alzheimers-dementia/signs-symptoms/index.html (2025).
3. Braak, H. & Braak, E. Neuropathological stageing of Alzheimer-related changes. Acta Neuropathol. (Berl.) 82, 239–259 (1991).
4. Pathological correlates of late-onset dementia in a multicentre, community-based population in England and Wales. The Lancet 357, 169–175 (2001).
5. Stern, Y. What is cognitive reserve? Theory and research application of the reserve concept. J. Int. Neuropsychol. Soc. 8, 448–460 (2002).
6. Snowdon, D. A., Greiner, H. & Wekstein, D. R. Linguistic Ability in Early Life and Cognitive Function and Alzheimer’s Disease in Late Life.
7. Snowdon, D. A. Aging and Alzheimer’s Disease: Lessons From the Nun Study. The Gerontologist 37, 150–156 (1997).
8. Stern, Y., Alexander, G. E., Prohovnik, I. & Mayeux, R. Inverse relationship between education and parietotemporal perfusion deficit in Alzheimer’s disease. Ann. Neurol. 32, 371–375 (1992).
9. Stern, Y. et al. Relationship between lifetime occupation and parietal flow: Implications for a reserve against Alzheimer’s disease pathology. Neurology 45, 55–60 (1995).
10. Stern, Y. Cognitive reserve. Neuropsychologia 47, 2015–2028 (2009).
11. Franzmeier, N. et al. Left frontal cortex connectivity underlies cognitive reserve in prodromal Alzheimer disease. Neurology 88, 1054–1061 (2017).
12. Stern, Y., Gazes, Y., Razlighi, Q., Steffener, J. & Habeck, C. A task-invariant cognitive reserve network. NeuroImage 178, 36–45 (2018).
13. Jones, R. N. et al. Conceptual and Measurement Challenges in Research on Cognitive Reserve. J. Int. Neuropsychol. Soc. 17, 593–601 (2011).
14. Satz, P., Cole, M. A., Hardy, D. J. & Rassovsky, Y. Brain and cognitive reserve: Mediator(s) and construct validity, a critique. J. Clin. Exp. Neuropsychol. 33, 121–130 (2011).

Cover photo by Vitaly Gariev on Unsplash.

Claude Sonnet 4.6 was used like an advanced search engine to identify key papers and to identify jargon/confusing ideas.