In a world still grappling with the consequences of a global pandemic, social connections are not what they used to be. Mask mandates, social distancing, and virtual meetings left many with feelings of social isolation. Loneliness is on the rise, especially among young adults. This “loneliness epidemic” increases the vulnerability of individuals to a plethora of mental and physical ailments, including depression, anxiety, and cardiovascular disorders (1). 

Human well-being relies on intimate social connections. In a recent study published in Nature Neuroscience, a team of researchers led by Rebecca Saxe, a neuroscientist at the Massachusetts Institute of Technology, reported that social interaction is a basic human need, just like food and water (2). 

In their study, Saxe and her team subjected 40 healthy volunteers to 10 hours of either fasting or social isolation. After the mandated fasting or isolation period, the volunteers reported craving food and social contact, respectively. Using functional MRI, the scientists found that the midbrain, particularly the area associated with reward processing, became activated during these cravings. 

The anticipation of reward or punishment is a powerful modifier of behavior and drives humans to engage in activities with positive outcomes and avoid activities with negative outcomes (3). Positive social interactions serve as reward signals that activate reward processing circuits in the brain in the substantia nigra pars compacta and the ventral tegmental area (SN/VTA) (2, 4). Neurons in these regions release dopamine to stimulate feelings of pleasure (6). 

People experience dopamine release positively and it provides an impetus to fulfill an unmet need. Participants in the study experienced the lack of intimate connections, as a feeling of loneliness, which provoked them to seek social contact (2). However, other studies have implicated chronic loneliness in structural changes to the midbrain that correspond with a decreased dopamine response. These structural changes correlated with behavioral changes that led people to become inhibited, fearful, and less trusting of others, while simultaneously making them self-centered and avoidant (6). 

The findings from these studies highlight the importance of intimate social connections for a healthy brain and mental well-being. Digital technologies played a crucial role during the pandemic by virtually connecting individuals with their loved ones. Now, scientists are exploring whether or not digital social interactions stimulate the same reward circuits in the brain as physical interactions. Physical isolation sparked by the pandemic and the increasing loneliness epidemic suggest that physical social interaction may be simply irreplaceable. 

References

1. Weissbourd, R., Batanova, M., Lovison, V., Torres, E. Loneliness in America. How the pandemic has deepened an epidemic of loneliness and what we can do about it. Harvard Graduate School of Education. Making Caring Common Project https://mcc.gse.harvard.edu/reports/loneliness-in-america (2020). 
2. Tomova, L., et al. Acute social isolation evokes midbrain craving responses similar to hunger. Nat Neurosci  23(12), 1597-1605 (2020). 
3. Clark, A. M. Reward processing: a global brain phenomenon? J Neurophysiol  109(1), 1-4 (2013). 
4. Izuma, K., Saito, D. N., & Sadato, N. Processing of social and monetary rewards in the human striatum. Neuron  58(2), 284-294 (2008). 
5. Bressan, R. A., Crippa, J. A. The role of dopamine in reward and pleasure behaviour—review of data from preclinical research. Acta Psychiatr Scand Suppl  111(427), 14-21 (2005) 
6. Cacioppo, J. T., et al. In the eye of the beholder: individual differences in perceived social isolation predict regional brain activation to social stimuli. Journal of Cognitive Neuroscience  21(1), 83–92 (2009)