Loneliness and hunger share a home in the brain


Loneliness and hunger share a home in the brain


A new study has discovered that the same part of the brain is involved in craving company and craving food. This supports the notion that socialising is a basic human need, much like eating.

Loneliness has been suggested to not only weaken the immune system, but also has links to dementia, mental illness, and diabetes. With the ongoing COVID-19 restrictions in place, it is vitally important to continue to look out for signs of loneliness and continue to socialise.

Research in social animals has also shown that social interaction is as necessary and rewarding as eating and sleeping, but little research has been done in socialising in humans.

A study team at Massachusetts Institute of Technology (MIT) in Cambridge, USA, compared the brain activity in participants after they fasted for 10 hours with the brain activity after being deprived of any social contact for 10 hours.

“It’s a stronger intervention of social isolation than anyone had tried before,” says the study’s senior author Rebecca Saxe.


Favorite food and social activities

The team used functional magnetic resonance imaging (fMRI) to examine any changes in the participants’ brain activity when they saw images of their favourite foods or people enjoying socialising.

They found that a very small part of the brain called the substantia nigra was activated when craving both food and human contact. This part of the brain, which contains dopamine neurons, has also previously been linked to addictive drug cravings.

The substantia nigra was activated both when hungry people looked at pictures of food and when socially isolated people looked at images of socialising, while neutral images of flowers did not activate the region.

“People who are forced to be isolated crave social interactions similar to the way a hungry person craves food,” says Saxe. “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.”

The research appears in Nature Neuroscience.


Personalized images

The study involved 40 participants aged between 18 and 40 years old, and were mostly college students. Each participant was asked to list their top 20 favourite foods and social activities, which the scientists used to find images to provoke cravings during the fMRI sessions.

When the participants who were socially isolated, they were asked to surrender their mobile phones and laptops, and then spent 10 hours alone in a windowless room without any access to email or social media.

“There were a whole bunch of interventions we used to make sure that it would really feel strange, different and isolated […] 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 get it. They really were not allowed to see people.”

The participants were allowed to solve puzzles, play simple computer games, or read pre-agreed written texts which did not contain any social content to amuse themselves. They periodically completed questionnaires which rated their loneliness, discomfort, happiness, social craving, and how much they disliked isolation.

fMRI was then used to scan their brains after 10 hours of being socially isolated. They were also scanned on a normal day, and after 10 hours of fasting.



Craving and the substantia nigra

The amount of activity in the substantia nigra correlated with how much they craved social interaction or food, according to their own answers.

After 10 hours of isolation, subjects who reported feeling chronically isolated months prior to the study had weaker social cravings during the isolation session, and had less activity in their substantia nigra while looking at people socialising.

“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,” says Saxe.

Comparatively, craving food or social contact was also associated with two patterns of activation elsewhere in the brain.

“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 authors write.

The team now hope to study how social isolation can affect behaviour, and whether virtual contact can satisfy cravings for social interaction.

One limitation of the current study was that the participants were primarily healthy young adults who were socially well-connected, and so the scientists also hope to investigate how isolation affects different age groups – chronic loneliness disproportionately affects older people and adolescents.

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