Some 40 years ago the Beatles famously sang: “I get by with a little help from my friends.” Since then, neuroscience research has proved again and again that a strong network of friends and family can do more than help us get by; it can apparently help us live longer, recover from illness faster, function better, and keep our cognitive faculties intact longer.
New evidence even suggests that close contact with friends and relatives offers a protective effect against Alzheimer’s disease.
The latest research, published in Lancet Neurology in May by David Bennett and colleagues at Rush University, examined postmortem brain tissue from 89 donors participating in the larger Rush Memory and Aging Project. The researchers found plaques and tangles, the pathological hallmarks of Alzheimer’s, in many people who had no clinical signs of dementia or cognitive impairment.
By looking back at the social and lifestyle records of those people, the scientists determined that the relationship between cognitive performance and the amount of pathology changed with the size of one’s social network. When pathological changes were relatively minor, strong social integration did not make a difference in cognitive tests. But as pathology increased, the apparent protective effect of a vibrant social network on cognitive performance also increased.
Understanding the ‘How’
Bennett says the findings suggest that social networks may afford a “protective reserve” capacity that spares people the clinical manifestations of Alzheimer’s disease. This “reserve” theory, essentially a twist on the “use it or lose it” adage, has also been postulated as a reason why longer formal education is associated with a lower risk of Alzheimer’s.
The idea is that more learning—or more social engagement, which presumably involves social learning—results in more synaptic connections and richer neural pathways. These enable the brain to have greater flexibility, or plasticity—to access alternate pathways, for example, which may enable it to compensate for pathological changes caused by age or disease. Overt clinical signs may thus remain in check.
Another theory centers on a potential “stress-buffering” effect of social integration. A close, supportive social network may protect the brain by decreasing stress and sparing the brain from the damaging effects of glucocorticoids, the family of powerful stress hormones that are released when we are stressed.
Glucocorticoids alter synaptic plasticity and are toxic to neurons in the hippocampus, an important structure for learning and memory. Long-term exposure, as with chronic or repeated stress, impairs memory skills.
Marilyn Albert, a cognitive neuroscientist at Johns Hopkins University and an authority on brain aging, believes that psychosocial factors are important because they modulate stress hormones. She points to the original MacArthur Study of Successful Aging, which she and colleagues published in 1994. It was the first large epidemiological study to solidly link social engagement parameters to maintenance of cognitive function.
In the MacArthur Study, the researchers measured cortisol (a glucocorticoid) in participants’ urine and found a relation between lower cortisol levels and stronger social networks. Lower cortisol was in turn related to better cognitive performance in the same group of healthy 70- to 79-year-olds.
While scientists are still trying to sort out the “how,” the evidence that strong social connections are good for your brain has been building for two decades. Dozens of studies have correlated social connectedness with specific health outcomes, among them overall physical functioning, recovery from stroke or cardiovascular disease, and death by any cause. Several large studies have now looked at the impact of social factors on cognitive maintenance, using a variety of measures, and the positive association first revealed in the MacArthur Study has held up.
For example, a study funded by the National Institute on Aging and led by Claudia Kawas of the University of California, Irvine, has been following a group of 1,400 adults 90 and older since 1981 in an effort to identify lifestyle factors that influence healthy brain aging. Although the study is ongoing, Kawas says it is already clear that “people seem to do better if they get out of their houses and interact with other individuals.” The correlation is dose-dependent, Kawas adds: the more frequently study participants have contact with others, the better they do on cognitive tests.
“There is something about being involved with other people that makes a difference to brain health,” Albert says. “Whether the critical piece is knowing you have people you can turn to, or feeling that you are not isolated, or some other factor, we just don’t know yet. But it’s very tantalizing.”
The difficulty in studying social attributes in laboratory animals is one challenge that has hampered scientists’ ability to confirm the epidemiological findings, better understand what aspect of social engagement is most critical, and reveal the underlying physiological mechanisms. In contrast, physical activity, another lifestyle factor that has emerged as a fundamental tenet of brain health, has been extensively studied in laboratory animals, and these studies not only have solidified correlations but also have helped define the mechanisms at play.
Studies have examined animals that are caged in “enriched environments” that include social contact with other animals, but this model also affords the animal physical activity and exploratory learning, so it is difficult to know which factor is responsible for improvements in learning and memory.
Prospective, controlled clinical trials, the gold standard of medical research, also present a challenge because it would be unethical to restrict the social contact of human volunteers for any period of time. Still, a handful of researchers are finding ways to investigate social factors in a controlled way and track any change in cognitive performance (see sidebar).