Those cravings aren’t just cabin fever—the human body hungers for companionship in much the way we hunger for food, according to a new study conducted at the Massachusetts Institute of Technology.

The study may just shed some light into the phenomenon of lockdown fatigue—that is, why, for example, so many Americans are willing to ignore guidelines from the Centers from Disease Control and Prevention to stay at home this holiday season, or why anti-lockdown protests continue to bloom from Berlin to Columbus, Ohio. One possible reason? Humans may have this innate biological need to see each other. And restrictions, no matter how well intentioned, are messing with it.

The MIT study, conducted mostly on college-age volunteers in 2018 and 2019—before the pandemic—found that 10 hours without any social contact, for many people, led to a kind of psychological and physical craving that’s on the same level of intensity as 10 waking hours without food.

“People who are forced to be isolated crave social interactions similarly to the way a hungry person craves food,” said Rebecca Saxe, a professor of brain and cognitive sciences at MIT, and the senior author of the study, said in a release.

“Our finding fits the intuitive idea that positive social interactions are a basic human need, and acute loneliness is an aversive state that motivates people to repair what is lacking, similar to hunger.”

Ten hours of hunger, ten hours alone

The study was inspired by previous research that showed that the function of a cluster of neurons in mice’s brains is linked to the need for social interaction. The researchers knew that humans get agitated when confronted with a lack of social contact—but the neurological basis for those emotions wasn’t well known before, they said.

The study got a group of volunteers to undergo two separate stretches of observation: 10 hours without any social contact—including through their phones—and, on another day, 10 hours without food. At the end of both periods, the volunteers underwent MRI scans and were simultaneously shown images: in the first case, photos of people happily interacting; in the second, plates of food. Each time, researchers measured the brain activity of the subjects.

If fasting for hours sounds unpleasant, the researchers made sure the experience of being alone was well and truly miserable.

“There were a whole bunch of interventions we used to make sure that it would really feel strange and different and isolated,” said Saxe. “They had to let us know when they were going to the bathroom so we could make sure it was empty. We delivered food to the door and then texted them when it was there so they could go get it. They really were not allowed to see people.”

As predicted, the area of the brain impacted—the substantia nigra—was the same when the subject was derived of food and derived of human contact. Both experiences also lit up other, different parts of the brain, the researchers said—an area for further study.

The social butterfly effect

The researchers also noted that, when it comes to loneliness, previous experience may make you less vulnerable to such feelings of craving.

People who reported feeling isolated long before the study showed a more limited reaction to the 10 hours completely on their own, while people who reported active social lives—the social butterflies—felt much more distressed.

“For people who reported that their lives were really full of satisfying social interactions, this intervention had a bigger effect on their brains and on their self-reports,” said Saxe.

Before the pandemic, of course, the study offered a chance to open a door to the long term affects of isolation and loneliness—which have been linked to lower health outcomes. But this year, the experience of at least physical isolation was suddenly broadly felt, across countries and cultures, often for months at a time through imposed COVID lockdown measures.

Global lockdowns have offered a further window into just how much we need each other. Although many of us long ago concluded the answer to that one: an awful lot.

As for further areas of research, the researchers pointed to the impact of isolation on behavior, the difference based on age—and whether all those endless video calls actually help.