When was the last time you met a close friend, in real life, and not on a video call? When was the last time you were hungry? Chances are that both feelings -- of loneliness and of hunger -- spark the same kind of brain activity.
A new study by neuroscientists at the Massachusetts Institute of Technology (MIT) reveals that the longings we feel during social isolation share a neural basis with the food cravings we feel when we are hungry. The researchers found that after one day of total isolation, the sight of 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.
“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,” said Rebecca Saxe, the John W. Jarve Professor of Brain and Cognitive Sciences at MIT, a member of MIT’s McGovern Institute for Brain Research, and the senior author of the study. The research team collected the data for the study in 2018 and 2019, before the covid-19 pandemic and resulting lockdowns. Their findings, which were published in a paper in the Nature Neuroscience journal on 23 November, are part of a larger research programme that focuses on how social stress affects people’s behaviour and motivation.
MIT researchers enlisted the help of 40 healthy individuals, 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, but the room did have a computer that they could use to contact the researchers,” an MIT release explains. After the 10-hour isolation period, every individual was scanned using an MRI machine.
They also went through a 10-hour fasting session on a different day. They were then scanned while looking at images of food, 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, which has previously been linked with hunger cravings and drug cravings,” the release explains.
The researchers have hypothesized that the “craving signal” these 40 “socially isolated” subjects exhibited in their substantia nigra after looking at photos of people enjoying social interactions was similar to the signal produced when they saw pictures of food after fasting. This was not the only part of the brain that was analyzed for “activation patterns”. Researchers also looked at the striatum and the cortex, and found that hunger and isolation each activated distinct areas of those regions. “That suggests that those areas are more specialized to respond to different types of longings, while the substantia nigra produces a more general signal representing a variety of cravings,” the release says.
Saxe said that these new findings could help the researchers answer more questions, including how social isolation affects people’s behaviour, whether virtual social interactions, like video calls, help alleviate cravings for social interaction, and how isolation affects different age groups.
This new study has its origins in a paper based on a 2016 study on social isolation, which identified a cluster of neurons in the brains of mice that represent feelings of loneliness and generate a drive for social interaction following isolation. Gillian Matthews, a research scientist at the Salk Institute for Biological Studies and Kay Tye, a professor at the Salk Institute, were the authors of the 2016 study. The substantia nigra is believed to share evolutionary origins 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 release explains.
Both Tye and Matthews are also co-authors of the MIT study published on 23 November. Former MIT postdoc Livia Tomova, who is now a research associate at Cambridge University, is the lead author of the paper. Other authors include Kimberly Wang, a McGovern Institute research associate; Todd Thompson, a McGovern Institute scientist and Atsushi Takahashi, assistant director of the Martinos Imaging Center.
