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Since the onset of the coronavirus pandemic in the spring, many people have only seen their close friends and relatives on video calls, if at all. A new study from MIT reveals that the desires we feel during this type of social isolation share a neural basis with the food cravings we experience when we’re hungry.
The researchers found that after a day of total isolation, the sight of people having fun together activates the same region of the brain that lights up when someone who hasn’t eaten all day sees a picture of a plate of pasta with cheese.
“People forced to be isolated crave social interaction the same way a hungry person craves food. Our finding fits with the intuitive idea that positive social interactions are a basic human need, and acute loneliness is an aversive state that motivates people to fix what is lacking, like hunger, ”says Rebecca Saxe, John Brain Professor W. Jarve and Cognitive Sciences at MIT, Fellow of the McGovern Institute for Brain Research at MIT and lead author of the study.
The research team collected the data for this study in 2018 and 2019, well before the coronavirus pandemic and the resulting lockdowns. Their new findings, described today in Neuroscience of nature, are part of a larger research program focusing on how social stress affects people’s behavior and motivation.
Former MIT postdoctoral fellow Livia Tomova, now a research associate at the University of Cambridge, is the lead author of the article. Other authors include Kimberly Wang, a research associate at the McGovern Institute; Todd Thompson, a scientist from the McGovern Institute; Atsushi Takahashi, deputy director of the Martinos Imaging Center; Gillian Matthews, research scientist at the Salk Institute for Biological Studies; and Kay Tye, professor at the Salk Institute.
Social envy
The new study was in part inspired by a recent article by Tye, a former member of the Picower Institute for Learning and Memory at MIT. In this 2016 study, she and Matthews, then a postdoctoral fellow at MIT, identified a cluster of neurons in the brains of mice that represent feelings of loneliness and generate a need for social interaction after isolation. Studies in humans have shown that being deprived of social contact can lead to emotional distress, but the neurological basis for 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 social stress was,” says Saxe. “It’s a stronger social isolation intervention than anyone has attempted before.”
To create this isolated environment, the researchers recruited 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 did have a computer they could use to contact researchers if needed.
“There was a whole series of interventions that we used to make sure it would feel really weird, different, and isolated,” says 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 texted them when she was there so they could pick her up. They really weren’t allowed to see people.
After the 10 hour isolation was completed, each participant was scanned in an MRI machine. This posed additional challenges, as the researchers wanted to avoid any social contact when digitizing. Before the start of the isolation period, each subject was trained in how to enter the machine, so that they could do it on their own, without any help from the researcher.
“Normally getting someone into an MRI machine is actually a really social process. We engage in all kinds of social interactions to make sure people understand what we’re asking them, that they feel safe, that they know we’re there, ”says Saxe. “In this case, the subjects had to do everything on their own, while the researcher, who was dressed and masked, remained silent and observed.
Each of the 40 participants also underwent 10 hours of fasting on a different day. After the 10-hour isolation or fasting period, participants were scanned while viewing 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 tiny structure located in the midbrain that was previously linked to hunger and drug cravings. The substantia nigra is also believed to share evolutionary origins with a region of the brain in mice called the dorsal raphe nucleus, which is the area that Tye’s lab showed to be active after social isolation in their study of. 2016.
The researchers hypothesized that when socially isolated subjects saw pictures of people enjoying social interactions, the “withdrawal signal” in their substantia nigra would be similar to the signal produced when they saw pictures of food after fasting. It was indeed the case. Additionally, the amount of activation in substantia nigra correlated with how strongly patients rated their feelings of starvation or social interaction.
Degrees of loneliness
The researchers also found that people’s responses to seclusion varied depending on their normal level of loneliness. People who reported feeling chronically isolated months before the study ended showed lower urges for social interaction after the 10-hour isolation period than people who reported richer social lives.
“For people who reported that their lives were really filled with satisfying social interactions, this intervention had a greater effect on their brains and on their self-reports,” says 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 activated distinct areas of these regions. This suggests that these areas are more specialized in responding to different types of desires, while the substantia nigra produces a more general signal representing a variety of cravings.
Now that researchers have established that they can observe the effects of social isolation on brain activity, Saxe says they can now try to answer many more questions. These questions include how social isolation affects people’s behavior, whether virtual social contacts such as video calls help alleviate cravings for social interactions, 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 lockdowns imposed in the early stages of the coronavirus pandemic.
The research was funded by an SFARI Explorer grant from the Simons Foundation, a MINT grant from the McGovern Institute, the National Institutes of Health, including an NIH Pioneer Award, a Max Kade Foundation scholarship, and an Erwin Schroedinger scholarship from the Austrian Fund. for science. .
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