Bzdok, D., and Dunbar, R.
Nat Hum Behav 6, 1333–1343 (2022).https://doi.org/10.1038/s41562-022-01453-0
Abstract
Intense sociality has been a catalyst for human culture and civilization, and our social relationships at a personal level play a pivotal role in our health and well-being. These relationships are, however, sensitive to the time we invest in them. To understand how and why this should be, we first outline the evolutionary background in primate sociality from which our human social world has emerged. We then review defining features of that human sociality, putting forward a framework within which one can understand the consequences of mass social isolation during the COVID-19 pandemic, including mental health deterioration, stress, sleep disturbance and substance misuse. We outline recent research on the neural basis of prolonged social isolation, highlighting especially higher-order neural circuits such as the default mode network. Our survey of studies covers the negative effects of prolonged social deprivation and the multifaceted drivers of day-to-day pandemic experiences.
Conclusion
The human social world is deeply rooted in our primate ancestry. This social world is, however, extremely sensitive to the time we invest in it. Enforced social isolation can easily destabilize its delicate equilibrium. Many of the psychological sequalae of COVID-19 lockdowns are readily understood as resulting from the dislocation of these deeply rooted social processes. Indeed, many of these findings could have been anticipated long before the COVID-19 pandemic. For example, almost one in ten Europeans admitted never meeting friends or family outside of their own household in the course of an entire year, with direct consequences for their psychological and physical health. Solitary living made up >50% of households in a growing number of metropolitan cities worldwide and has long been thought to be the cause of increasing levels of depression and psychological dystopia. Indeed, aversive feelings of social isolation probably serve as a biological warning signal that alerts individuals to improve their social relationships.
Three key points emerge from our present assessment. One is that COVID-19 and associated public health restrictions to curb the spread of the virus are likely to have demonstrable mental health and psychosocial ramifications for years to come. This will inevitably place a significant burden on our health systems and societies. The impact may, however, be largely restricted to specific population strata. Older people, for example, are likely to face disproportionately adverse consequences. Worryingly, prolonged social isolation seems to invoke changes in the capacity to visualize internally centred thoughts, especially in younger sub-population. This may presage a switch from an outward to an inward focus that may exacerbate the experience of social isolation in susceptible individuals. The longer-term implications of this are, however, yet to be determined. Second, the experience of undergoing social isolation is known to have significant effects on the structure and function of the hippocampus and default network, long recognized as a primary neural pathway implicated in the pathophysiology of dementia and other major neurodegenerative diseases as well as in effective social function. The fact that these same brain regions turn up in the neuroanatomical consequences of COVID-19 infection is concerning. Our third key point is that social determinants that condition inequality in our societies have strong impacts on lived day-to-day pandemic experiences. This is highlighted by the negative outcomes from COVID-19 for families of lower socio-economic status, single-parent households, and those with racial and ethnic minority backgrounds.
As a note of caution, in our judgement, few datasets or methodological tools exist today to definitively establish causal directionality in many of the population effects we have surveyed in this review. For example, many of the correlative links do not allow us to infer whether loneliness directly causes depression and anxiety, as opposed to already depressed, anxious individuals being more prone to developing loneliness in times of adversity. Similarly, none of the reviewed findings can be used to tease apart whether changes in psychopathology during periods of mass social isolation are the chicken or the egg of the many biological manifestations. To fill knowledge gaps on mediating mechanisms for theoretical models, future research requires carefully designed and controlled longitudinal before-versus-after COVID-19 population investigations.
