Friday, December 05, 2008

Working Later in Life May Facilitate Neural Health

By: Denise C. Park Ph.D.

Evidence indicates that by continuing to perform difficult tasks and engage in new pursuits, the brain remains flexible over time—good not only for the individual but also for society. Denise C. Park theorizes that exercising the brain causes “scaffolding,” which creates new circuits to support pre-existing pathways.

Could working past age 65 prove beneficial to neural and cognitive health? Denise C. Park, director of the Productive Aging Laboratory at the University of Texas, suggests that continuing to engage in intellectual activities and new experiences keeps the brain running efficiently. Her theory of “scaffolding” holds that in such situations the aging brain develops new circuits that help people respond to cognitive challenges.

Wealthier countries are experiencing a rapid and significant increase in their aging populations, thanks to 1) increased longevity; 2) decreased birth rates and 3) the progression of the baby boomer population to older adulthood. Despite tremendous concern in American and other Western societies about the cost of health care and retirement benefits for this aging population, we too seldom ask what the consequences would be for both individuals and society if people continued to work well past 65 and retired at later ages. How would this affect individuals? Would the sustained social engagement and mental activity associated with many jobs and professions result in better cognitive health or would it lead to cognitive frailty? What about the effects upon society? Would a longer work life enhance social connectivity across generations, increase mental and physical health in older citizens and, accordingly, lower health care costs? We must learn more, but I believe that the answer to all of these questions is yes.

We know surprisingly little about the effects of continued engagement in work on neural and cognitive health. Cognitive frailty is almost certainly the most important age-associated health problem that we confront as a society.

We must learn how to slow cognitive aging. Work in my laboratory as well as many others has demonstrated that even healthy older adults show some decline in memory and in the speed at which they process information. Slowing down the process of cognitive aging would help individuals maintain the skills they need to live independently for their entire lives.

Cognitive Engagement May Maintain the Brain

Broad research into mental activity and engagement suggests that continuing employment might be a plus for individuals. Maintaining an active mind or staying deeply engaged in meaningful activities in late adulthood could help sustain a high level of cognitive function. Nearly all the available evidence suggests that an active, engaged lifestyle—both intellectual and social—across one’s life span is associated with enhanced cognitive health and a later age of onset of dementing illnesses; large-scale demographic studies suggest that engaging in reading and other intellectual activities is associated with delayed onset of Alzheimer’s disease.1 These findings have two possible explanations: One is that cognitively healthy individuals stay deeply engaged throughout their life span, and the association of engagement with good cognitive health occurs because those who are less healthy slowly disengage over many years. The other, more attractive, possibility is that actually staying active and engaged sustains cognitive health, maintains intellectual vitality and staves off Alzheimer’s disease and other dementing illnesses.

Teasing apart the relationship between lifetime mental engagement and cognitive health is not an easy task; scientists can’t conduct an experiment in which they randomly assign one group to retire at age 60 and another to retire at age 75. If sustained engagement in work promotes cognitive health, the later retirees should do better than the earlier retirees. Studies do hint at answers.

Evidence Emerges

Carmi Schooler at the National Institutes of Health, using a technique that allowed him to assess causal relationships, found that adults who performed intellectually challenging jobs across their life span showed more cognitive flexibility in late adulthood than those who performed less demanding jobs.2 

More recent work in the neurosciences also suggests that novel experiences may indeed increase cognitive health and even the size of parts of the brain, providing a neural reserve that could help us maintain function into old age. Animal studies clearly demonstrate that rats or dogs that experience an enriched and stimulating environment, even one introduced in old age, learn better and have greater brain volume than animals in less-enriched environments. Research in humans also suggests that stimulation and sustained learning may play a role in brain growth, even with age. One seminal study revealed that London taxicab drivers who had spent many years finding their way through the complex streets of London had larger hippocampi—a brain area active during way finding and navigation—than age-matched control subjects. Of particular relevance to the question of the impact of work on cognitive aging, the effect of cab driving on hippocampal size was more pronounced with more years of experience, suggesting that sustained work as the cab driver got older magnified the effect.

 Perhaps the most compelling evidence regarding the impact of novel experiences on brain volume and function comes from a study at the Max Planck Institute in Germany. Adults with a mean age of 59 spent three months learning to juggle three balls. Although only about half the participants were able to achieve competence in this complex skill, those who succeeded had increased volume in a mediotemporal area of the visual cortex as well as the nucleus accumbens and the hippocampus, suggesting that sustained novel experience can increase the sizes of neural structures. Notably, the changes in the nucleus accumbens and hippocampus were transient, disappearing three months after the juggling ceased. This intriguing study provides clear evidence that continued skill performance is necessary to maintain some gains from experience, and it strongly supports the “use it or lose it” adage.

Drawing meaning from these findings in the realm of work and everyday life in older adulthood is not an entirely straightforward exercise, however. Although structural increases in brain tissue based on novel experience are exciting, they do not mean that continued engagement in the workforce will maintain cognitive health into old age. Few jobs in late adulthood entail continuous challenge and the learning of complex new skills and behaviors, which the studies I’ve described suggest is important for neural health and growth. In fact, I have argued that most jobs that older adults hold are characterized by “maintenance functions,” tasks that rely on knowledge and well-practiced skills rather than active new learning.

Neural ‘Scaffolding’

The aging brain may be ripe for the latter—active learning is likely to have a significant cognitive payoff. Patricia Reuter-Lorenz and I have argued that the brain is remarkably adaptive in response to the neural challenges that are part of normal aging. Our Scaffolding Theory of Aging and Cognition (STAC) suggests that the aging brain, when confronted with the joint challenge of declining neural resources and a cognitively demanding task, develops “scaffolds”—new circuitry that helps maintain task performance.3 Evidence for neural scaffolding emerges from functional imaging studies showing that older adults typically engage more brain tissue than young adults when performing a demanding cognitive task. Most often, this additional activity is in a region in the opposite hemisphere from an area active in young adults as well (“bilateral recruitment”) or in an area larger than that seen in the young adults (“penumbral activation”). Evidence from my lab and others has provided clear documentation that this additional scaffolding is compensating for areas of the brain that are functioning somewhat less efficiently than in younger adults.

According to the STAC model, neural scaffolding that occurs with age is similar to the development of new circuitry when, at younger ages, we acquire a new skill or learn new information. As we age, scaffolding develops not just in the context of new learning but also to maintain a response when other neural structures or circuitry are no longer sufficiently healthy to meet the challenge of a cognitive task. We suggest that the defining feature of a healthy brain is the ability to continue the scaffolding process in response to challenge. A particularly important tenet of the STAC model is that cognitive activity promotes this ability. On the other hand, the collapse of the scaffolding process is characteristic of various forms of dementia (though the cause of the collapse will be different for different dementia types). With the STAC model as a guide, a critically important goal of late adulthood should be to maintain the ability of the brain to change and respond to cognitive challenge. To the extent that social structures can foster the maintenance of this ability with age, older people might have a higher quality of life and be more able to contribute to the vitality of the economy. Policies that encourage active participation in the workforce into late adulthood, such as providing corporate incentives for new training and incentives to individuals for training and accepting new challenges, would help.

Following the STAC model, let us explore the cognitive demands of a relatively routine job and the cognitive challenges it might represent. Consider a receptionist for a large medical practice. In order to be effective, a receptionist has to stay on top of scheduling, remember who’s who among patients and respond to different physicians’ individual preferences. Invariably, new software for patient management, new phone procedures, and new insurance forms will be introduced. These considerable memory demands will require scaffolding, and we can see how functioning in such a context might better stimulate one’s neural health than would a quiet life at home or even a retreat to the golf course, where events are highly routine and usually require little adaptation to circumstances.

At the same time, neither work nor leisure inherently requires ongoing cognitive challenges, and the demands of different types of jobs can be quite deceptive. One can imagine that something as mundane as being a Wal-Mart greeter could have a significant memory load (e.g., learning the names of repeat customers, keeping special sales in mind each day, etc.) or offer essentially no stimulation or opportunities for scaffolding (e.g., automatically welcoming each customer in a repetitive fashion). Similarly, a leisure-filled lifestyle is not inherently unhealthy—variety, challenge and stimulation are possible. Someone who volunteers as a museum guide and has several active hobbies may experience considerably more cognitive challenge than he or she did in the workforce. The STAC model posits that scaffold development occurs as a result not of work or leisure per se but of situations that are optimally challenging to the cognitive system and that engage many different domains of cognition, including attention, working memory, long-term memory, and activation of knowledge systems.

Testing the Scaffolding Theory

Although many aspects of the STAC model are broadly accepted, such as the notion that the aging brain expands areas of activation in response to cognitive challenge, other important facets are more speculative. The model suggests that continuous cognitive challenge and breadth of stimulation in a novel environment would promote more scaffolding and greater brain health. To test this hypothesis, I, along with my colleague Jennifer Lodi-Smith, have developed a learning environment that we call Synapse. We are enrolling research participants into the Synapse environment and providing them with a demanding program that will require 20 hours of their time per week for 14 weeks. Participants will be novices at quilting and digital photography and will be enrolled in a class that specializes in one, the other, or both. They will receive instruction and work on increasingly challenging projects that will stimulate cognitive, motor, and social function. We will compare their cognitive performance, brain structure, and neural function (as gauged by functional magnetic resonance imaging) to results in individuals who participate in exclusively social activities, in self-paced learning tasks at home, or in a control group that does not participate in activities. We hypothesize that the group that learns multiple skills with the combination training will develop the greatest number of scaffolds and will show enhanced attention and memory, as well as more selective recruitment of neural resources. We hope that the skills acquired by Synapse participants will provide continued benefits even after the participants leave the program and that these gains (or at least protection against cognitive loss) will endure.

If older people have jobs that include cognitive challenges similar to those we are creating, our research suggests that they may be able to maintain a healthier brain. Although we have much to learn about the aging mind and how to preserve its vitality, new imaging tools are allowing us to take giant steps as we examine these questions further. One of the premier challenges of the 21st century lies in determining what behaviors will protect neural health and then developing public health initiatives to encourage these behaviors in our communities. Sound social policies that encourage older people to keep working will have direct benefits to our economic system. It also could be neuroprotective, resulting in later onset of dementing illnesses, an outcome that offers gains for society thanks to reduced caregiving and health care costs, as well as extended time with beloved family members.

References

1. R. S. Wilson and D. A. Bennett. “Cognitive Activity and Risk of Alzheimer's Disease,” Current Directions in Psychological Science 12 (2003): 87.

2. C. Schooler, M. S. Mulatu, and G. Oates. “The Continuing Effects of Substantively Complex Work on the Intellectual Functioning of Older Workers,” Psychology and Aging 14 (1999): 483–506.

3. D. C. Park and P. Reuter-Lorenz. “The Adaptive Brain: Aging and Neurocognitive Scaffolding,” Annual Review of Psychology (forthcoming).



About Cerebrum

Bill Glovin, editor
Carolyn Asbury, Ph.D., consultant

Scientific Advisory Board
Joseph T. Coyle, M.D., Harvard Medical School
Kay Redfield Jamison, Ph.D., The Johns Hopkins University School of Medicine
Pierre J. Magistretti, M.D., Ph.D., University of Lausanne Medical School and Hospital
Robert Malenka, M.D., Ph.D., Stanford University School of Medicine
Bruce S. McEwen, Ph.D., The Rockefeller University
Donald Price, M.D., The Johns Hopkins University School of Medicine

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