Social isolation triggers cravings in the brain similar to hunger
A study using fMRI scanners has found that just 10 hours of total isolation can leave the brain feeling starved.
Professor Rebecca Saxe is a professor of cognitive neuroscience and associate department head at the Department of Brain and Cognitive Sciences at MIT. In a recent study, her team found that the same area of the brain reacts to social isolation as to food cravings.
How do you study cravings, when they are so subjective?
A standard way is to study hunger. You have people fast for much longer than they typically would if they were hungry, then you show them pictures of the food they would like to eat, and you get a craving response in the brain.
Subjectively, people can tell you how they feel. But there is also a small, fine structure, deep in the brain, called the ‘substantia nigra’ which produces dopamine.
It seems to be the best measure we have as a source of that feeling of craving. What we wanted to do in this study was to see whether that same neural circuit would be involved if you’d been isolated and given a reminder of what you were missing.
How did you go about it?
Each volunteer agreed to do one day where they didn’t eat all day and one day where they didn’t see people or interact with people in any way – neither virtually nor live.
At the end of each day, we then showed them pictures of their favourite foods, and of their favourite social activities.
[Using an MRI scanner], we measured brain activity in the substantia nigra to see if we could reproduce what we already expected – that there would be a bigger response to food when the volunteers were hungry, and whether that same brain region would show a response to pictures of social interaction when they had spent a day being isolated.
Read more about social isolation:
- Hikikomori: identifying extreme social isolation around the globe
- Lockdown: why is social isolation so hard?
What did you find?
In the substantia nigra, the main area we were looking at, we found that both food cues when you’re hungry and social cues when you’re isolated evoke this basic craving response. This is incredibly interesting, that it worked in a straightforward, similar way [whether hungry for food or hungry for social interaction].
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Were you surprised that the effect was seen after just one day?
When we designed the study, one of the main things that we debated was whether 10 hours would be long enough. And also, would the volunteers still feel isolated if they knew exactly when it was going to end? We had to tell our participants what they were volunteering for, so they knew it was only a day.
We found that, for most of us, a day of isolation does produce cravings in the brain. But it affects different people to different degrees.
We found that both food cues when you’re hungry and social cues when you’re isolated evoke this craving response
Surely studying someone requires some degree of social interaction?
A whole puzzle was how do you get a person into an MRI machine without social interaction? Normally, participating in scientific research is a very social experience. We will talk to you about what we’re doing, why we’re doing it and what you should expect. We’ll then talk you through the process of getting into the MRI machine and will make sure that you’re okay.
Actually, figuring out how to get a person into an MRI scanner, without any social interaction, was the main challenge of the studies. We had to train the people in advance to get themselves into the scanner.
We had the minimum number of researchers involved and had them gowned and masked so that the volunteers couldn’t see them or see any social interaction between them.
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Can your experiment tell us anything about the current situation in which many people are self-isolating?
When we started out, we just couldn’t imagine that there would be a context in which people would become isolated in this way. But now here we are in this semi-isolated state that will go on for weeks and weeks.
However, the isolation that our participants experienced was much more acute. What we’re experiencing [with COVID-19] is a longer term, more mixed isolation where there are some people around and we have access to all forms of media, including our phones.
But for the 10 hours of isolation that our participants experienced, they didn’t have any interaction from anybody at all.
Are there any immediate implications to the findings?
We were inspired by a study that had done a similar thing in mice. And what we found in our study is that regions involved in craving social interaction is analogous to what our collaborators have found when they studied it in mice.
That result was a key part of our original motivation, because there are research labs all over the world that use mice as the main experimental animal to test new ideas about mental health treatments, especially drug treatments. For example, studying social motivation in mice is a way people can test potential treatments for autism.
Do you have plans for future studies?
The post-doc in my lab is moving to Cambridge University this summer to follow up on the research in a bunch of ways, including looking at how social media influences experiences of isolation. She will also look at the experiences of adolescents, because despite being wildly connected on social media, adolescents actually report really high levels of loneliness.
One of the things we said in the paper, which is really important, is that although we can objectively isolate people, subjective loneliness is very different.
Being alone doesn’t always mean being lonely, and being connected is not always enough to fulfil your social needs. She is particularly interested in the causes and predictors of loneliness in adolescents and that’s what she’s going to study next year.
Jason is the commissioning editor for BBC Science Focus. He holds an MSc in physics and was named Section Editor of the Year by the British Society of Magazine Editors in 2019. He has been reporting on science and technology for more than a decade. During this time, he's walked the tunnels of the Large Hadron Collider, watched Stephen Hawking deliver his Reith Lecture on Black Holes and reported on everything from simulation universes to dancing cockatoos. He looks after the magazine’s and website’s news sections and makes regular appearances on the Instant Genius Podcast.