Since the coronavirus pandemic began in the spring, many people have only seen their close friends and loved ones, if at all, during video calls. A new study by MIT finds that the longing we feel during this kind of social isolation shares a neural basis with the hunger we feel when hungry.
The researchers found that after one day of complete isolation, seeing people having fun together activates the same brain region that lights up when someone who hasn’t eaten all day sees a picture of a plate of cheesy pasta.
“People who are forced into isolation crave social interactions in much the same way as a hungry person craves food. Our finding fits with the intuitive notion that positive social interaction a basic human need, and acute loneliness is an adversarial state that motivates people to repair what is rare, much like hunger, “said Rebecca Saxe, John W. Jarve Professor of Brain and Cognitive Sciences at MIT, a member of the Institute McGovern for MIT Brain Research, and senior author of the study.
The research team collected the data for this study in 2018 and 2019, well before the coronavirus pandemic and resultant locks. Their new findings, described today in Neuroscience of Nature, is part of a larger research program that focuses on how social stress affects people’s behavior and motivation.
Former MIT postdoc Livia Tomova, now a research associate at Cambridge University, is the lead author of the paper. Other authors include Kimberly Wang, research associate of the McGovern Foundation; Todd Thompson, a scientist from the McGovern Institute; Atsushi Takahashi, assistant director of the Martinos Imaging Center; Gillian Matthews, research scientist at the Salk Institute for Biological Studies; and Kay Tye, a professor at the Salk Institute.
The new study was inspired in part by a recent paper by Tye, a former member of MIT’s Picower Institute for Learning and Memory. In that 2016 study, she and Matthews, a MIT backpacker at the time, identified a cluster of neurons in the brain of mice that represent feelings of loneliness and generate a campaign for social interaction following isolation. Studies in humans have shown that being deprived of social contact can lead to emotional distress, but the neurological basis of these feelings is not well known.
“We wanted to see if we could experimentally induce a certain type of social stress, where we would have control over what the social stress was,” Saxe said. “It’s a stronger intrusion of social isolation than anyone had ever tried before.”
To create that isolation environment, the researchers enlisted healthy volunteers, mostly college students, and confined them to a windowless room on the MIT campus for 10 hours. They were not allowed to use their phones, but the room had a computer that they could use to contact the investigators if needed.
“There was a whole bunch of interventions we used to make it really feel weird and different and isolated,” Saxe said. “They had to let us know when they went 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 they were going to get it. They couldn’t do it. see people. “
After the 10-hour isolation was complete, all participants were scanned in an MRI machine. This posed additional challenges, as the researchers wanted to avoid any social contact during the scan. Before the isolation period began, each subject was trained on how to enter the machine, so that they could do it alone, without any assistance from the researcher.
“Getting someone into an MRI machine is usually a very social process. We take part in all kinds of social interactions to make sure people understand what we’re asking them, that they they feel safe, they know we are there, “Saxe said. “In this case, the subjects had to do it all on their own, while the researcher, who was sewn and hidden, just stood silent while watching.”
Each of the 40 participants also received 10 hours of fasting, on a different day. After the 10-hour isolation or fasting period, participants were scanned looking at images of food, images of people interacting, and neutral images such as flowers. The researchers focused on a part of the brain called the substantia nigra, a very small structure located in the mid-brain, previously linked to hunger and drug cravings. The substantia nigra is also thought to share evolutionary roots with a brain region in mice called the dorsal raphe nucleus, which is the area that Tye’s lab showed was active following social isolation in their 2016 study.
The researchers hypothesized that when socially isolated subjects would see pictures of people enjoying social interaction, the “craving signal” in their substantia nigra would be similar to the signal produced when viewing pictures of food after fasting. This was true. Furthermore, the degree of activation in the substantia nigra was correlated with how strongly patients rated their feelings of craving for either food or social interaction.
Degrees of loneliness
The researchers also found that people’s responses to loneliness vary depending on their normal levels of loneliness. People who reported feeling chronically isolated months before the study were shown showed weaker desires for social interaction after the 10-hour isolation period than people who reported a richer social life.
“For people who reported that their lives were truly filled with satisfying social interaction, this intervention had a greater impact on their brains and on their self-reports,” said Saxe.
The researchers also looked at activation patterns in other parts of the brain, including the striatum and cortex, and found that hunger and isolation each activate specific areas of those regions. That suggests that those areas are more specialized to respond to different types of nostalgia, while the substantia nigra produces a more general signal that represents a variety of cravings.
Now that the researchers have established that they can observe the effects of social isolation on brain activity, Saxe says they can now try to answer many additional questions. Those questions include how social isolation affects people’s behavior, whether virtual social connections like video calls help alleviate a craving for social interaction, and how isolation affects different age groups.
The researchers also hope to study whether the brain responses they saw in this study could be used to predict how the same participants responded to isolation during the locks set during the early stages of the coronavirus pandemic.
The research was funded by a SFARI Investigator Grant from the Simons Foundation, an MINT grant from the McGovern Foundation, the National Institutes of Health, including the NIH Innovator Award, Max Kade Foundation Fellowship, and the Austrian Science Fund Erwin Schroedinger Fellowship. .