Social isolation is a complex phenomenon to evaluate. Compared to other stimuli, it could be better understood as a lack thereof. Accordingly, evaluating the consequences of social isolation can be challenging but the importance of this task has arguably never been more evident with emerging negative health repercussions of COVID-19 protocols. Another complex phenomenon that has been tied to social isolation is addiction, which can be defined as a brain disorder characterised by patterns of compulsive behaviour such as drug seeking, and repeatedly engaged despite severe consequences. Addictive behaviours are estimated to have risen dramatically since the onset of the COVID-19 pandemic. The alignment of these trends highlights the need to further investigate how these two phenomena are mechanistically connected─an ongoing pursuit over the past half century.

In the mid 20th century, most of the research on how addictive substances affect behaviour involved studies with rats kept in small, solitary cages. The rats were given access to two drinking bottles: one laced with an addictive substance (usually cocaine), and one with just water. In this setting, rats would often neglect the clean water and begin to obsessively consume the drug-laced water until they eventually overdosed and died. This picture represents the accepted understanding at the time of how the “addictiveness” quality of a substance was considered to be the main and only factor that led to repeated self-administration despite the risk of overdose and overall detriment to health.

By 1979, Dr. Bruce Alexander—a psychologist from Vancouver—began to question this assumption and set out to change some key parameters to these experiments. He devised experiments where rats had access to two water sources where one was laced with cocaine and the other was clean; only now, he gave the rats expansive social environments with plenty of space, food, toys, and mates. These experiments gained the moniker “Rat Park” because it was similar to putting the rats in an amusement park where they could have anything they ever wanted. At the end of the experiments, the rats living in Rat Park had overdosed on the available substances at a significantly lower rate. Thus, a growing hypothesis emerged that social isolation may be a factor in the susceptibility to developing all kinds of addictive behaviours.

With more and more studies showing that isolated rodents became addicted to substances with greater frequency than rats with opportunities for social activity, the mechanism of exactly how social isolation influenced addiction vulnerability still remains largely unknown. Nevertheless, a 2023 physiology literature review conducted at the University of Toronto has put forward a potential mechanistic pathway by which these two complex phenomena are connected. By aggregating the literature on observed changes evoked by social isolation in the prefrontal cortex area of the brain and examining the patterns in these findings that coincide with a higher probability of exhibition of addictive behaviours, structural and functional patterns were found. Social isolation appears to reduce the opportunity for connections between a subtype of neurons in the medial [middle] prefrontal cortex due to a loss in surface area. Consequently, these neuron populations have a hindered ability to communicate with other neuron populations in the limbic region of the brain, an area critical for modulating behaviour related to motivation and reward. This type of dysfunction in these cells has been consistently connected to short-term reward-seeking behaviour, lower impulse control, and impaired decision making─all of which are established markers of addiction vulnerability.

While this mechanistic pathway represents a narrow portion of all the interacting structural and functional regions of the brain that are known to be implicated in social isolation and addiction, it remains a step in the direction of understanding how these factors interplay in the context of a real-world social issue. Furthermore, the exploration of the physical connection between social isolation and addiction can prompt future experiments that examine the causal relationship more directly, demonstrates the value of making use of primary research beyond the applications that were intended for it when it was originally published, and even then helps lead to the identification of potential physical targets for addiction therapy.

On a broader scale, pursuing an understanding of the physiological underpinnings of social isolation and addiction represents an opportunity to reckon with major world events in a new light. Ultimately, understanding the repercussions of social isolation can prompt us to take steps towards addressing the harm that addiction presents in people’s lives, and grow more cognizant of the wellness value associated with fostering community and togetherness.