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Neuroscience has the power to invest familiar truths with excitement, presenting them as utterly new. So it is with a report published in the journal Nature Neuroscience last week, which shows how people who have been deprived of all social contact for one day crave contact with others in a way that is similar to the food cravings of those who are hungry. [1] Common experience tells us we need others, but the quirky and compelling findings of this study offer us an in-brain view of what we already know.
The study was inspired by the identification, a few years earlier, of neurons in the brains of mice that are activated by isolation and push mice to interact with others. [2] To explore whether these neural mechanisms play any part in humans, the researchers recruited 40 young, healthy adults, most of whom were college students, and kept them confined to a windowless room for 10 hours. During that time, they could not use their phones, and the bathroom had to be checked before they used it to make sure it was empty. Even the MRI procedure was conducted in as isolated an environment as possible, with a masked attendant silently standing by.
When, after the 10 hours of isolation, the participants were shown images of people who were smiling and socializing, the activity in a tiny midbrain structure—the substantia nigra—produced what is recognized from other studies on hunger and drug dependency as a craving signal. This neural signal also flared when, on a different day, the participants fasted for 10 hours and were then shown pictures of cheese-laden pizza. The intensity of the neural response was nicely correlated with how severely the students rated their subjective feelings. Those who reported, “I feel very lonely,” also showed a more intense craving signal.
Though the notion that the same brain area responded in the same way to hunger and to social need has been the headline in discussions of this study, there were important differences between the overall neural responses to hunger and to social isolation. Other brain areas also registered the cravings, but here (in the striatum and cortex), they were different for loneliness and for hunger.
It is not surprising that the response to social isolation is so basic, so primitive. Our human ancestors lived in social groups, dependent on one another for information, food, and protection. Isolation would have been synonymous with death. We can see the psychologically evolved effects in reports from people who have experienced solitary confinement. Shane Bauer, who was imprisoned in Iran in 2009, explained, “No part of my experience—not the uncertainty of when I would be free again, not the tortured screams of other prisoners—was worse than the four months I spent in solitary confinement... I needed human contact so badly that I woke every morning hoping to be interrogated.”
Similarly, Nelson Mandela, who spent 27 years in prison under the South African Apartheid regime, said, “Nothing is more dehumanizing than the absence of human companionship.” As Frans de Waal writes, “Second to the death penalty, solitary confinement is the most extreme punishment we can think of. It works this way only, of course, because we are not born as loners." [3]
Often in neuroscience studies, the brain activity revealed is intriguing because we already know how such neural activity feels. We should never lose sight of what we already know about humans when we assess such studies. Here, our broader experience of human responses might lead us to challenge the scope of the research.
Is this particular craving signal age-sensitive? Young college students who participated in the study are at a crucial age of social engagement, when they are exploring their identities vis-à-vis others. They are also learning how to function away from the families on which they have been intimately dependent since birth. Would older people respond in the same way?
There is another question raised by a special condition that the participants had to meet. “No social interaction” included a ban on “fiction.” In other words, humans' enduring attraction to stories about other people, their delight in novels, plays, films, soaps, and gossip, was denied during this 10 hour period. At some point, we need a study that varies the conditions so that we might discover whether imaginative engagement with other people provides some social nourishment. As the damage wrought by isolation is an increasing concern, so must we learn what might ease it.
The study was completed before so many young people were subjected to social isolation as a consequence of the pandemic and social distancing. The participants’ conditions—alone in a windowless room—reminds me of the conditions experienced by some students on college campuses, with food left outside their door, with the need to check any common area such as a bathroom or kitchen to ensure they would not come into contact with other people. The self-isolating college students may have been able to talk to others on their phones and even to wave to people outside their windows, but their isolation went on for much longer. For those who did not previously dwell on the real pain generated by such conditions, this study will persuade them to do so now.
References
1. L. Tomova, et.al. (2020). Acute social isolation evokes midbrain craving responses similar to hunger. Nature Neuroscience. 23:12. 1597.
2. G. Matthews, et.al. (2016). Dorsal Raphe Dopamine Nuerons Represent the Experience of Social Isolation. Cell. 164:4. 617-631.
3. F. de Waal. (2009). Primates and Philosophers: How morality evolved. S. Macedo &J.osiah Ober (Eds.). Princeton,NJ: Princeton University Press, p.5.
