COVID-19 and Mental Health: How Social Isolation Impacts Your Brain

Currently, we are facing one of the worst pandemics in human history. Since our means to fight the virus are still limited, social distancing has been the best way to contain the crisis. While in many countries this is still necessary, it is important to know that social isolation (SI) has many negative repercussions on mental health.

Human beings are social animals. Unlike other animals, we do not have sharp claws or fangs, we cannot run very fast, nor can we jump from tree to tree. Our survival largely depends on being part of a group. We have evolved to react to forced isolation from our peers as a threat to our survival. Our body reacts by activating its stress response.

When we feel lonely, our prefrontal cortex and limbic system send a cascade of signals to the hypothalamus. The paraventricular nucleus (PVN) of the hypothalamus answers by secreting corticotropin-releasing hormone, which in turn stimulates the secretion of adrenocorticotropic hormone by the anterior pituitary, the adrenal glands’ cortex answers by releasing cortisol. This is the hypothalamus-pituitary-adrenal (HPA) axis. Our sympathetic nervous system also becomes hyperactive and, through its nerves, stimulates the release of adrenaline and other similar compounds by the adrenal glands’ medulla. The result is high levels of cortisol and catecholamines in our blood, setting the whole body into a fight or flight response.

The stress response itself is a normal and healthy reaction to a threat. It becomes a problem, however, when it is sustained for weeks or months, as it may well be during a protracted, pandemic-enforced social isolation period. SI has already been linked to an increased risk of cardiovascular diseases, inflammatory conditions, immunodepression, and psychiatric disorders, amongst other health conditions. In fact, the increase in the mortality rate of socially isolated people can be as high as 32%, comparable to those of smokers and heavy drinkers.

Social isolation exerts its adverse effects through the development of affective disorders, such as depression and anxiety. In this context, one study in Singapore showed a correlation between loneliness and depression in adults. It is interesting to note that the biggest correlation was with the subjective experience of loneliness – not with indicators of SI, such as connectedness with relatives and friends. Another study in older adults in the USA revealed that SI is not only linked to the prevalence of depression and anxiety, but also to the severity of the symptoms. The occurrence of depression- and anxiety-like behaviours such as anhedonia (the lack of interest in positive stimuli), aggressiveness, and neophobia (the aversion to new stimuli) has also been shown in lab animals subjected to SI.

There are mechanisms that our body uses to control the damage caused by our stress responses. One of them is the release of a peptide called oxytocin by neurons in the PVN. There are many published studies on animal models showing that oxytocin can prevent SI-induced behavioral alterations, such as anhedonia, and aggression. It also reduces immobility in the forced swim test, which infers an animal motivation by measuring how long the rodent is willing to keep trying to scape a swimming pool with no exit. Some of the health impacts of SI can also be mitigated by oxytocin. An experiment on prairie voles revealed that oxytocin reduces SI-induced oxidative damage and telomere reduction. Another one showed that all the alterations caused by sympathetic hyperactivation, such as increased basal heart rate, reduced heart rate variability, and vagal regulation of the heart, are also prevented by oxytocin.

Unfortunately, oxytocin signaling itself is negatively impacted by SI. Indeed, oxytocin is known more for its role in the regulation of social affiliation than the regulation of stress. When an individual is separated from its peers, oxytocin’s gene expression in the PVN is diminished, and from that, we can infer that so is its production. What’s more, the expression of its receptor both in the brain and in other organs, such as the heart, is reduced. Thus, the effects of SI on health may not solely be attributed to an overactive HPA axis, but also to decreased oxytocin signaling.

Evidence for the pandemic’s impact on mental health is already emerging, urging the development of strategies to address the negative consequences of SI. Unfortunately, there is surprisingly little evidence to guide strategies to mitigate this problem, especially considering that increasing social connectedness is just not enough to address SI-related loneliness. On the other hand, SI is still necessary in many places for the containment of COVID-19. Thus, telecommunication technology is one possible tool we can turn to reduce the damage caused by SI. Research shows that, while not a substitute for real-life interactions, communication through the internet and telephone can still provide meaningful social support and help to reduce social isolation in the short term.

As social animals, our brains are not wired to live in isolation and trying to do so exposes us to physical and mental harm. In the long-term, SI activates our body stress response, making us susceptible to illness. To avoid this, people should do their best to remain connected to others until the virus is under control or until new strategies to tackle the negative effects of SI are developed.

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How have recent lockdown measures treated you? All of us in the Knowing Neurons team hope that everyone is well during these difficult times.

Interested in more Mental Health content, our interview with Dr. Shekhar Saxena, the Director of the Department of Mental Health and Substance Abuse at WHO, raises awareness on how Mental Health is part of health.

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— Written by Sophia La Banca. Illustrated by Sumana Shrestha.

References

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