Dr. Yaakov Stern is the Division Leader of the Cognitive Neuroscience Division of the Sergievsky Center, and Professor of Clinical Neuropsychology, at the College of Physicians and Surgeons of Columbia University, New York. Alvaro Fernandez interviews him here as part of our research for The SharpBrains Guide to Brain Fitness book.
Dr. Stern is one of the leading proponents of the Cognitive reserve theory, which aims to explain why some individuals with full Alzheimer’s pathology (accumulation of plaques and tangles in their brains) can keep normal lives until they die, while others ‑with the same amount of plaques and tangles- display the severe symptoms we associate with Alzheimer’s Disease. He has published dozens of peer-reviewed scientific papers on the subject.
The concept of a Cognitive Reserve has been around since 1989, when a post mortem analysis of 137 people with Alzheimer’s Disease showed that some patients exhibited fewer clinical symptoms than their actual pathology suggested. These patients also showed higher brain weights and greater number of neurons when compared to age-matched controls. The investigators hypothesized that the patients had a larger “reserve” of neurons and abilities that enable them to offset the losses caused by Alzheimer’s. Since then, the concept of Cognitive Reserve has been defined as the ability of an individual to tolerate progressive brain pathology without demonstrating clinical cognitive symptoms.
- Lifetime experiences, like education, engaging occupation, and leisure activities, have been shown to have a major influence on how we age, specifically on whether we will develop Alzheimer’s symptoms or not.
- This is so because stimulating activities, ideally combining physical exercise, learning and social interaction, help us build a Cognitive Reserve to protect us.
- The earlier we start building our Reserve, the better; but it is never too late to start. And, the more activities, the better: the effect is cumulative.
The Cognitive Reserve
Alvaro Fernandez (AF): Dear Dr. Stern, it is a pleasure to have you here. Let me first ask you this: the implications of your research are pretty broad, presenting major implications across sectors and age groups. What has been the most unexpected reaction so far?
YS: well…I was pretty surprised when, years ago, a reporter from Seventeen magazine requested an interview. I was really curious to learn why she felt that her readers would be interested in studies about dementia. What she told me showed a deep understanding and insight: she wanted to motivate children to stay in school. She understood that early social interventions could be very powerful for building reserve and preventing dementia.
AF: Very insightful…let’s now fast forward, say, 60 years from our high-school years, and suppose that persons A and B both technically have Alzheimer’s (plaques and tangles appear in the brain), but only A is showing the disease symptoms. What may explain this discrepancy?
YS: Individuals who lead mentally stimulating lives, through education, occupation and leisure activities, have reduced risk of developing Alzheimer’s. Studies suggest that they have 35–40% less risk of manifesting the disease. The pathology will still occur, but they are able to cope with it better. Some won’t ever be diagnosed with Alzheimer’s because they don’t present any symptoms. In studies that follow healthy elders over time and then get autopsies, up to 20% of people who did not present any significant problem in the daily lives have full blown Alzheimer’s pathology in their brains.
AF: What exactly may be going on in the brain that provides that level of protection?
YS: There are two ideas that are complementary. One idea (called Brain Reserve by researchers) postulates that some individuals have a greater number of neurons and synapses, and that somehow those extra structures provide a level of protection. In a sense, we have more “hardware”, providing a passive protection against the attacks of Alzheimer’s. The other theory (called Cognitive Reserve) emphasizes the building of new capabilities, how people can perform tasks better through practice, and how these skills become so well learned that they are not too easy to unlearn. Like developing new and refined “software”.
AF: But, both seem to go hand in hand, correct? Neuroplasticity means that what you call “hardware” and “software” are two sides of the same coin and they influence each other, right?
YS: Correct. So these days we don’t make a sharp distinction, and are conducting more neuroimaging studies to better understand the relationship between both.
Building Your Cognitive Reserve
AF: So our goal is to build that Reserve of neurons, synapses, and skills. How can we do that? What defines “mentally stimulating activities” or good “brain exercise”?
YS: In summary, we could say that “stimulation” consists of engaging in activities. In our research almost all activities are seen to contribute to reserve. Some have challenging levels of cognitive complexity, and some have interpersonal or physical demands. In animal studies, exposure to an enriched environment or increased physical activity result in increased neurogenesis (the creation of new neurons). You can get that stimulation through education and/ or your occupation. There is clear research showing how those two elements reduce the risk. Now, what is very exciting is that, no matter one’s age, education and occupation, our level of participation in leisure activities has a significant and cumulative effect. A key message here is that different activities have independent, synergistic, contributions, which means the more things you do and the earlier you start, the better. But you are never stuck: better late than never.
AF: Can you give us some examples of those leisure activities that seem to have the most positive effects?
YS: For our 2001 study we evaluated the effect of 13 activities, combining intellectual, physical, and social elements. Some of the activities with the most effect were reading, visiting friends or relatives, going to movies or restaurants, and walking for pleasure or going on an excursion. As you can see, a variety. We saw that the group with high level of leisure activities presented 38% less risk (controlling for other factors) of developing Alzheimer’s symptoms. And that, for each additional type of activity, the risk got reduced by 8%. There is an additional element that we are starting to see more clearly. Physical exercise, by itself, also has a very beneficial impact on cognition. Only a few months ago researchers were able to show for the first time how physical activity promotes neurogenesis in the human brain. So, we need both mental and physical exercise. The not-so-good news is that, as of today, there no clear recipe for success. More research is needed before we prepare a systematic set of interventions that can help maximize our protection.
AF: We typically emphasize the importance of a good nutrition, physical exercise, stress management and mental exercise that presents novelty, variety and challenge. What do you think of the relatively recent appearance of so many computer-based cognitive training programs, some more science-based than others?
YS: Those elements you mention make sense. The problem is that, at least from the point of view of Alzheimer’s, we cannot be much more specific. We don’t know if learning a new language is more beneficial than learning a new musical instrument or using a computer-based program. A few of the cognitive training computer programs we have seen, like the one you discussed with Prof. Daniel Gopher to train the mental abilities of pilots, seem to have clear effects on cognition, generalizing beyond the training itself. But, for the most part, it is too early to tell the long-term effects. We need better designed clinical trials with clear controls. Right now, the most we can say is that those who lead mentally stimulating lives, through education, occupation and leisure activities seem to have the least risk of developing Alzheimer’s Disease.
AF: Tell us know a bit more about your current research
YS: We are studying a number of related areas, applying neuroimaging techniques to understand how exactly all these Cognitive Reserve concepts are implemented in the brain.
One, we want to understand individual differences in how people approach tasks. We want to measure their efficiency and capacity the brain networks that mediate tasks performance with the idea that those with greater efficiency and capacity might cope better with age-related problems. For example, we can all understand that a competitive swimmer is going to swim better than I would even if he has some weights in his legs, but we haven’t yet identified what exactly is the equivalent in the brain.
Second, we want to understand how old people compensate for the areas of decline. For example, do they begin to use new brain areas when the ones that are typically used start to fail.
Third, whether the Cognitive Reserve presents benefits beyond the prevention of Alzheimer’s symptoms. Does having a higher reserve result in better attention, better executive functions, more successful aging overall?
AF: All very important topics. Thank you for your time, and please keep us informed.
YS: My pleasure. Thank you for your great educational initiative.
Stern Y. Cognitive reserve and Alzheimer disease. Alzheimer Dis Assoc Disord. 2006, 20:112–117.
Scarmeas N, Albert SM, Manly J, Stern Y. Education and rates of cognitive decline in incident Alzheimer’s disease. Journal of Neurology, Neurosurgery, and Psychiatry, 2006;77:308–316.
Scarmeas N, Stern Y. Cognitive reserve and lifestyle. J Clin Exp Neuropsychol 2003;5:625–633.
Stern Y, Zarahn E, Hilton HJ, Flynn J, DeLa Paz R, Rakitin B. Exploring the neural basis of cognitive reserve. J Clin Exp Neuropsychol 2003;5:691–701.