When people are forced to isolate themselves from others, after a short period of time they experience an increased need for social interaction. When they see pictures of people talking, laughing together or interacting in some other way, they react in a similar way to hungry people who see a picture of their favorite food. As researchers have shown using MRI images, the same regions in the midbrain are activated in both cases. The focus of attention is narrowed to the object of desire, while other stimuli are less attractive.
In the course of the corona pandemic, many people significantly reduced their contacts in order to avoid infection. But those who are chronically lonely often suffer from numerous physical and psychological consequences. These can include tiredness, nervousness, sleep problems and depression, as studies show. Even a comparatively short social isolation is therefore noticeable in our brain activity. Studies on mice have already shown earlier that animals kept alone at times tend to be more addictive and are particularly keen to seek social contact. This behavior is mediated by dopaminergic neurons in the midbrain. These are part of the reward system that responds to both positive social contacts and addictive substances.
Uncomfortable isolation
A team led by Livia Tomova from the Massachusetts Institute of Technology (MIT) has now carried out experiments on how temporary social isolation affects people. To do this, they cut 40 test persons off from any interpersonal interaction for ten hours: Alone in a room, they were only allowed to engage in non-social activities such as Sudoku, puzzles and texts without social content. In addition to personal contacts, digital communication, games or fictional texts with a social component were also prohibited.
For comparison, the same subjects were asked to fast for ten hours on a different day and eat nothing but water. At the beginning of the study as well as after the isolation and fasting, the test subjects indicated how much they long for social contact or food. They also went through an MRI scan, during which they were presented with various visual stimuli: pictures of their favorite dishes, of social activities or as a comparison of flowers. To make the results as comparable as possible, the researchers used photos from picture agencies. The subjects depicted were therefore not known to the test persons. In a previous survey, however, they had stated that they found appropriate social activities – such as conversations or fooling around together – as pleasant.
Characteristic brain activity
As expected, all test subjects stated after the fast that they were hungry and therefore felt uncomfortable. After ten hours of isolation, 36 out of 40 test persons stated that they felt more lonely than before, longed for social contact and were dissatisfied with the isolation. “Both forms of withdrawal evoke a desire to satisfy the need that has not been fulfilled, accompanied by general malaise and reduced happiness,” the researchers conclude. In doing so, they point out that it is challenging to create a feeling of loneliness experimentally: “Loneliness is not simply a product of objective isolation. People can be alone without feeling lonely, or they can feel lonely in the midst of a crowd. “
During the MRI scans, the researchers focused particularly on the substantia nigra and the ventral tegmental area in the midbrain. These regions are rich in neurons that release the messenger substance dopamine and that play a role in addiction and desire. It is already known from mice that these brain regions are involved in the response to social withdrawal. As the brain scans showed, these areas also reacted in the test subjects: After fasting, the reactions to pictures of food were significantly stronger than to pictures of social activities. After isolation, however, the corresponding brain regions were activated more strongly by images of interacting people than by images of food. The response was all the more pronounced, the more lonely the subjects felt according to their answers in the questionnaire.
“Overall, these results suggest that the substantia nigra and the ventral tegmental area show an increased response to social stimuli after social isolation, with the spatial pattern being similar to the response to food stimuli in hungry people,” write Tomova and colleagues.
Interaction as a basic human need
To the surprise of the researchers, however, the brain reaction to the desired stimulus was only marginally stronger than in the initial scan, in which the test subjects neither had to forego food nor social contact. Instead, the difference between the stimuli resulted from the fact that the test subjects reacted weaker to all other stimuli afterwards. The researchers explain: “At the beginning of the study, the motivation of the participants may have been divided between several sources of reward. Specific acute withdrawal may result in narrowing and focusing the brain’s motivational response to the neglected need rather than amplifying the response itself. If a need is not met, this could reduce the motivation to pursue other needs. “
Only people who have a stable social network and are in regular contact with friends took part in the study. The more intense their usual social activities, the more they missed social contacts after isolation and the more pronounced their brain reactions were. The researchers therefore restrict the fact that the results may only be transferable to a limited extent to people who already have few social interactions, such as old people who are particularly prone to loneliness.
In view of the corona pandemic, which is leading to a restriction of their social contacts for large parts of the population, further research is therefore necessary – also with regard to the extent to which digital communication can replace face-to-face meetings. “Overall, our results fit the intuitive idea that positive social interactions are a basic human need and that acute loneliness is an uncomfortable situation that motivates people to regain what they lack, similar to hunger.”
Source: Livia Tomova (Massachusetts Institute of Technology, Cambridge) et al., Nature Neuroscience, doi: 10.1038 / s41593-020-00742-z