All the Lonely People—What Do They All Think Of?

Paradoxically, people who are lonely may have more active social brains.

One of the loneliest years in living memory comes to a close tomorrow, and the announcement last week of the first reported cases of COVID-19 in Antarctica has driven home how far-reaching this pandemic really is—that even in the most lonely, socially isolated landscape in the world, people are not safe from the coronavirus.

But the pandemic has also laid bare the problems that arise from loneliness itself, which even in the most crowded metropolitan population centers of the world can have a crushing impact on human health.

Loneliness has made major headlines this year as social distancing measures have forced more people to stay indoors and away from in-person interactions. Loneliness has been a constant theme in the agonizing tales of people dying alone in hospital beds with loved ones unable to visit them. And the prevalence of loneliness during lockdown has been the subject of scientific debate as some research has pointed to an increase in loneliness during the pandemic while other earlier reports suggested steady levels of loneliness throughout the pandemic.

What nobody argues about is the fact that loneliness is linked to massive health problems, especially in older people. And in our modern era, in which the progress of science has helped people live longer than ever, there’s evidence that loneliness has been increasing for decades.

It comes at a cost. Perceived social isolation feeds despair, fuels depression, contributes to alcoholism, causes high blood pressure and insomnia, and leads to more rapid progression in Alzheimer’s disease. People who are lonely also take longer to recover from surgery. It affects our physical and mental health, impacts our cognitive performance, and decreases our overall life expectancy. Some experts even claim that being lonely is the equivalent of smoking 15 cigarettes a day.

But while we appreciate the massive and sometimes severe impact of loneliness on health, we don’t really understand the biology linking loneliness to poor health outcomes. Are people more sick because they are lonely, more lonely because they are sick, or a little of both?

“We know that loneliness is impacting the brain, but we don’t really know what the mechanisms are,” says Nathan Spreng, a researcher at McGill University who published a new study in Nature Communications with his colleagues this month that may have uncovered a portion of this mystery.

“Do you often feel lonely?”

Humans are social animals. Our social life is intense and complex, and scientists believe that over the course of evolution, the human brain evolved to develop an extremely powerful capacity for navigating sophisticated social interactions. We constantly track the words and deeds of other members of our social groups, decode their complex social meaning, recall past things our companions said or did, and relate those old memories to subtle new social cues to navigate any number of challenging social interactions every day of our lives.

There is no way to look at a brain scan and tell if someone is lonely the same way you might identify brain cancer or a stroke.

However the exact neurophysiology that lends itself to that ability has never been identified. There is no way to look at a brain scan, for instance, and tell if someone is lonely the same way you might identify brain cancer or a stroke.

So Spreng and his colleagues took a population-level approach to the problem, looking at fMRIs and other brain scans of 40,000 people 40–69 years old through the U.K. Biobank, a public resource that bundles together brain scans, full-sequence genomic data, and other information taken from half a million people who are part of Britain’s National Health Service.

They were able to segment those 40,000 people into two groups, lonely or not, because all the Biobank volunteers filled out a simple survey when they enrolled, which included the question, “Do you often feel lonely?” Some 13 percent of the Biobank participants responded “yes” (39 percent were men and 61 were women), which is consistent with overall reported estimates of the prevalence of loneliness in European countries.

Dividing the population into two groups based on an answer to a single, simple question may seem a somewhat unsophisticated way of defining loneliness, where shades of gray are likely more the reality than black and white, but it is nonetheless a valid and widely used approach, according to McGill University neurologist Leslie Fellows, an expert who was not involved in the research.

A striking result

Analyzing tens of thousands of brain scans helped researchers link loneliness to a set of regions across the brain known as the “default network,” which is involved in many higher-order cognitive processes, including memory and social cognition. It is also a key network implicated in human social behavior. 

“This network of regions has long been associated with reflecting on oneself and other minds, as well as remembering and anticipating the future,” says Andrea Courtney, a postdoc at the Stanford Social Neuroscience Lab who works in the same field but was not involved in the research.

Paradoxically, what the McGill study shows is that in the brains of the Eleanor Rigbys, Father McKenzies, and all the other lonely people in the world, the default networks are actually larger, more active, and more connected than in people who are not lonely.

“It was quite striking,” Spreng says. “We tended to see people who were lonelier had a higher integrity of that network.” In the absence of actual human interactions, he says, “There is stimulation or imagination of that feeling of social connection.’

Why should people who feel socially isolated have more activity or interconnectivity in the social parts of their brains?

“It’s like putting in a three-lane highway where you see single-lane traffic.”

What Spreng and his colleagues think is happening is that these changes are induced—the plastic brain’s way of compensating for the feeling of loneliness. People may be filling social voids by reminiscing more about past social experiences, imagining future social interactions, or anthropomorphizing their pets, talking to them as people and treating them as one would a human companion.

“This study provides another crucial link between the phenomenology of loneliness and individual differences in brain structure and function,” says Courtney, the Stanford postdoc.

It may also explain a well-known connection between loneliness and Alzheimer’s disease. People who are lonely and have Alzheimer’s progress more rapidly to dementia than people with Alzheimer’s who are not lonely, possibly because the greater integrity of connections in the brains of lonely people may allow the disease to spread more rapidly. “It’s like putting in a three-lane highway where you see single-lane traffic,” Spreng says. He was recently named recipient of a $2.7 million National Institutes of Health grant to study this connection.

“This work is a nice example of trying to better understand the biological mechanisms that underlie well-established social determinants of health, such as loneliness, stigma, poverty, and low education,” says Fellows, the McGill University neurologist.

“In the long run, this kind of interdisciplinary work may provide new ways of thinking about how individual neurobiology relates to the social environment, an environment which, of course, is created by lots of individual brains interacting together.”

Except, of course, during a pandemic.

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