Mar 30, 2021 9:00 AM

The Weird Science of Loneliness and Our Brains

Social isolation has been linked to poorer physical and mental health, but scientists are finally starting to understand its neurological impact.

Extreme isolation does strange things to the human mind. In late 1964 Josie Laures and Antoine Senni disappeared into two caves in the French Alps as part of an experiment to find out what effect isolation would have on their bodies and minds. When Senni emerged after 126 days in isolation—a record at the time—he thought that only a couple of months had passed. In 1972 Michel Siffre, a French caver who oversaw the pair’s experiment went even further, spending six months in a cave near Del Rio, Texas. “Physically it was not tiring, but mentally it was hell,” he told Der Spiegel four decades later.

Attempts to manufacture isolation in the laboratory are even more disturbing. In the 1950s, Canadian psychologist Donald Hebb paid graduate students at McGill University $20 a day to stay alone in tiny rooms. The volunteers’ hands were placed in cardboard tubes, their ears covered by thick U-shaped pillows to muffle any sounds, and opaque goggles were placed over their eyes. Soon enough their mental cognition deteriorated and they experienced extreme restlessness and vivid hallucinations. One student reported feeling that his body was in two places at once, and he was unable to decide which one was really him.

Humans rarely experience such extreme social isolation, but studies have shown that even in normal life, increased loneliness has a negative impact on physical and mental health. One review of the science of loneliness found that people with stronger social relationships have a 50 per cent increased likelihood of survival over a set period of time compared with those with weaker social connections. Other studies have linked loneliness to cardiovascular disease, inflammation, and depression.

We’ve known since the 1980s that people who are more socially isolated tend to have worse health, but we still don’t know why loneliness is so closely linked to our health. Is it that isolated people tend to have other risk factors for certain diseases, or is there something about loneliness itself that rearranges the wiring of our brains, slowly wearing away at our health? For loneliness researchers the pandemic has provided an unprecedented natural experiment in the impact that social isolation might have on our brains. As millions of people across the world emerge from months of reduced social contact, a new neuroscience of loneliness is starting to figure out why social relationships are so crucial to our health.

Although the link between loneliness and poor health is well-established, scientists have only recently been able to take the first glimpses of what social isolation looks like in our brains. It’s a discovery that started with a failed experiment. As part of her PhD at Imperial College London, Gillian Matthews was trying to find out how drug addiction affected the connections between specific neurons in a part of the brain called the dorsal raphe nucleus (DRN). Matthews divided the mice she was studying into two groups—one she injected with cocaine, and the other with a saltwater solution—but no matter what she tried, she kept seeing that the DRN neuron connections were growing stronger in both groups of mice.

These new neural connections, Matthews realized, had little to do with drugs. Both groups of mice had been isolated for 24 hours before the start of the experiment. What Matthews was seeing was the effect that social isolation had on the brains she was studying. This accidental discovery opened up a new way of thinking about loneliness—if we could see the traces of social isolation in the brains of mice, it meant that loneliness didn’t just describe a state in the outside world, it could also point to something on the inside too.

Matthews’ realization shunted her career in a new direction. Leaving her research on drug addiction to one side, in 2013 she went to the Massachusetts Institute of Technology to join Kay Tye’s laboratory. Tye is a neuroscientist focused on understanding the neural basis of emotion, and she’s also one of the pioneers of optogenetics—a technique that uses genetically engineered proteins inserted into brain cells to give researchers the ability to turn neurons on and off by shining light through fiber-optic cables into the brains of live animals. The approach lets scientists activate regions of the brain in real time and watch how the animals respond. “At the point I joined the lab, optogenetics was really exploding, and it opened up so much more potential for the studies that you could do,” Matthews says.

Armed with this new technique, Matthews and Tye wanted to figure out how DRN neurons influenced mice during social isolation. When the researchers stimulated the neurons, the animals were more likely to seek out other mice. When they suppressed the same neurons, even isolated animals lost the desire for social interaction. It was as if Matthews and Tye had located the neural switch that controlled the animals’ desire for social interaction—it turned on when they were isolated and turned back off again when their social cravings were satisfied.

Their discovery could radically change our understanding of loneliness. “Taking that idea suggests that there are mechanisms in place to help maintain social contact in the same way that there are mechanisms in place to make sure we maintain our food intake or our water intake,” Matthews says. It suggests that social contact isn’t just nice to have—it’s a fundamental need that our brains are hardwired to seek out. This is already borne out in studies on honeybees, ants, mice, and rats. “Without the full level of social contact, survival reduces in numerous species,” Matthews says.

In 2020 another MIT neuroscientist released a paper suggesting that human brains respond to social isolation in a way similar to Matthews’ mice. Livia Tomova recruited 40 volunteers and asked them to turn in their smartphones, tablets, and laptops and spend 10 hours in a room by themselves. The volunteers could occupy themselves with puzzle books and writing materials, but they weren’t allowed access to any fiction that might contain a hint of social contact that might take the edge off their isolation. If the volunteers needed to use the bathroom, they had to wear earplugs that prevented them from overhearing any conversations on the way. “We tried to create a scenario where people would really not have any sort of input,” says Tomova, who is now at the University of Cambridge.

Optogenetics is too invasive to use on humans, but instead Tomova took fMRI scans of her volunteers’ brains. When the isolated volunteers were shown photos of social cues, the regions of their brains associated with cravings lit up with activity in the same way that the brains of hungry people lit up when they were shown pictures of food. The area of the brain that Tomova focused on is rich in dopamine neurons, which drive our motivations and expectations of the world around us. When our brains anticipate a rewarding activity—like eating or social contact—these neurons activate in anticipation. But if we don’t get these interactions, then our brains experience a negative, craving-like feeling.

Tomova says that this might explain the negative consequences of long-term isolation. “If you are in a state of prolonged stress, the same adaptations that are in the first place healthy and necessary, will actually become detrimental because they’re not designed to be long-term states,” she says. “The idea of the cravings is that the goal should be to seek out others and reinstate social contact.”

These findings raise all kinds of questions for understanding of social isolation and its impact on health. Are there neurological differences between people who experience short-term isolation and those who have been isolated for long stretches of time? What kinds of social interactions satisfy our social cravings? Is a video call enough to quell our need for social contact, or do some people require an in-person connection to really feel satiated?

Despite knowing about the link between social isolation and health for decades, we don’t have satisfying answers to any of these questions yet. “There is this evidence that has been around a long time, but the unfortunate part is that it has been so underrecognized,” says Julianne Holt-Lunstad, a psychology professor at Brigham Young University in the US and the author of two major studies on social isolation and health. “We have a lot of data that very robustly shows that both isolation and loneliness put us at increased risk for premature mortality—and conversely, that being socially connected is protective and reduces our risk,” she says.

Holt-Lunstad thinks the pandemic could be a turning point in our understanding of loneliness. “I’m really hopeful that this is a huge wake-up call, you know, a point of reflection for us to learn from this,” she says. In 2018 the UK government launched its first loneliness strategy, and the NHS has already started directing people towards social clubs and other activities in an effort to reduce loneliness. “This is a public health issue, and it should be prioritized as such,” says Holt-Lunstad. “And as policies are being implemented, those policies should be evaluated and revised if needed.”

Solving the problem of loneliness—and understanding what helps and what doesn’t—will mean getting to grips with the different kinds of isolation people experience. We don’t know much about what happens when people go from a state of loneliness to one of social connection, says Andrew Steptoe, professor of psychology and epidemiology at University College London. He has been studying the health of people who go from living alone to living with someone else, but it’s hard to pinpoint which effects are down to changes in social isolation and which are caused by other factors.

“Trying to investigate isolation or loneliness is not as straightforward in humans. In humans, being lonely is not necessarily correlated with how many people are around you,” says Tomova. She is particularly interested in the impact that the pandemic might have had on young people whose cognitive and social skills are still developing. “I think we will see potentially some differences in how their social behavior developed or things like that,” she says. But as is always the case in the uncertain world of loneliness research, the opposite could be true. “It could also be that most people are fine, because maybe social media does fulfill our social needs really well.”

This story originally appeared on WIRED UK.