The neuroscientists behind the study found that after a single day of total isolation, the sight of a group of people having fun together activates the same brain region that lights up when someone who hasn't eaten for a day sees a picture of food.
Measuring the impact of social isolation
Over the years, studies into human behavior have shown that being deprived of social contact can lead to emotional distress, but the neurological basis for these feelings has not been thoroughly examined.
"People who are forced to be isolated crave social interactions similarly to the way a hungry person craves food," Rebecca Saxe, the senior author of the study, explained in a press statement.
"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," she continued.
The research team collected the data for their study in 2018 and 2019, before the coronavirus pandemic and social isolation guidelines came into force.
Their new findings, detailed in Nature Neuroscience, form part of a larger research program focusing on the impact of social stress on people's behavior and motivation.
"We wanted to see if we could experimentally induce a certain kind of social stress, where we would have control over what the social stress was,” Saxe said. "It's a stronger intervention of social isolation than anyone had tried before."
The researchers enlisted healthy volunteers, mainly college students, and confined them to a windowless room on MIT's campus for 10 hours. They were not allowed to use their phones, though the room did have a computer the volunteers could use to contact the researchers if necessary.
"There were a whole bunch of interventions we used to make sure that it would really feel strange and different and isolated," Saxe said. "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."
Once the 10-hour isolation period finished, each of the volunteers was scanned in an MRI machine. Importantly, the researchers wanted to avoid any social interaction for the volunteers during the scanning process. Each volunteer, therefore, was trained before their isolation period, on how to get into the MRI scanner, so that they could do it while isolated.
Separately, each of the 40 volunteers underwent 10 hours of fasting on a different day. Following this fasting period, MRI scans were once again taken of all the volunteers.
'Craving signal' correlation
After both the isolation periods and the fasting, the participants had MRI scans taken while looking at images of people interacting, and food respectively, as well as neutral images of flowers as controls.
The researchers focused specifically on the part of the brain called the substantia nigra, which has previously been linked with hunger and drug cravings. The researchers found that when the volunteers saw photos of people enjoying social interactions, the "craving signal" in their substantia nigra was similar to the one produced when they saw food after fasting.
The brain signals also correlated with how strongly the patients rated their cravings for food or social interaction on a number scale.
The researchers say that, following on from their findings, they now hope to work towards a better understanding of how social isolation affects people's behavior and whether virtual contact via video calls effectively alleviates those cravings.
In a year marked by social isolation, the researchers also aim to look into the way each of the volunteers has reacted to isolation measures put in place due to COVID-19 in order to help further our understanding of the impact of the pandemic.