Written By Sydnee A. Fry
An Overview of Loneliness
Throughout all historical and biological standards, humankind has always been known as a social species. From an evolutionary perspective, social relationships were vital to survival and reproduction; the worst-case scenario for neolithic humans was to lose shared predatory vigilance and access to resources such as food and mates (Vitale & Smith, 2022a). While these scenarios become irrelevant in the modern world, our evolved self-preservation processes continue to thrive--even under maladaptive conditions.
Loneliness is the brain's way of warning the self of possible social threats. In chronic cases, perceived social isolation can lead to poor physical health, including higher chances of cognitive decline, cardiovascular disease, and dementia, along with a heightened risk of mental health disorders like anxiety and depression. It is essential to note the difference between objective social isolation, following the number of friends and the frequency of social meetings, and subjective social isolation, including unmet social needs and perceived social disconnectedness. In fact, "subjective and objective measures of social isolation are only weakly correlated at about r=0.20" (Finley & Schaefer, 2022, para. 3). Although an objective isolation issue can be solved analytically, the cure for subjective levels of loneliness delves deep into neuroscientific theories and how the human mind interprets social interactions.
Neurobiological Theories
Reactional Theories
In psychology, two significant theories cover neurobiological reactions and loneliness: John Cacioppo’s Evolutionary Theory of Loneliness and George Slavich’s Social Safety Theory. Cacioppo proposes a conserved biological process focusing on self-preservation and social threat sensitivity. His theory views loneliness as an adaptive signal for our ancestors to promote social connectedness, leading to higher chances of survival. On the other hand, Slavich's Social Safety Theory highlights the body's stress response when one perceives social detachment. Under such conditions, an individual undergoes an immune response to prepare for physical injuries, decreasing the body's preparedness for any viral infections (Finley & Schaefer, 2022).
While both biological processes would be helpful in a hunter-gatherer situation, these become maladaptive in the long term. Following Cacioppo's mechanism, a vicious cycle where the lonely individual begins to interpret all social contexts negatively develops, leading to higher feelings of loneliness and defensiveness. In a study performed at the University of Chicago's Center for Cognitive and Social Neuroscience, lonely individuals observed hypervigilance towards social threats and a higher chance to mislabel emotional expressions as unfavorable, along with faster identification of negative emotional faces (Cacioppo et al., 2015). Under the malicious cycle, perceived social isolation becomes a more prominent issue to solve, as our prediction of a negative outcome to every interaction cannot be changed by objective means.
Insular Cortex Theory
Other research explores the relationship between the insular cortex and the interpretation of social interactions. Barrett and Simmon's (2015) interoceptive predictions in the brain view the insular cortex as the newfound hub for processing social interactions; it theorizes that the brain uses previous knowledge in "prediction neurons" found in the angular insular cortex to create what the body considers the best reaction. However, as the insular cortex controls processes of exteroception (incoming sensory information) and interoception (internal knowledge), previous bias from social relations and our perceived connectedness can lead to discrepancies between reality and personal belief. The agranular insular cortex transmits predictions in chemical signals to dysgranular and granular insular layers, which leads to the reduction and amplification of the firing rate of neurons in anticipation of contrasting sensory information to previous bias (Vitale & Smith, 2022a). Ultimately, our mind's predictions that all attempts at social connection will end badly drive our negation of present sensory information.
Figure 1
Schematic of proposed insular cortex activity in lonely individuals
Note. Prediction neurons (pictured in green) remain inflexible against incoming sensory signals to dysgranular and granular insular cortexes. Simultaneously, negative valence in stimuli is addressed more intensely than positive valence, leading to a lower chance of recognizing the error in the prediction neurons (Vitale & Smith, 2022b).
Adverse Physical and Mental Effects
Hypothalamic-Pituitary-Adrenal Axis
The hypothalamic-pituitary-adrenal (HPA) axis plays a significant role in the harmful effects of social isolation. Neuropeptides such as glucocorticoids and corticotrophin-releasing hormones often increase during social ostracization, leading to high levels of anxiety and depressive behaviors. As the HPA axis is critically involved in regulating glucocorticoids (such as cortisol), activation of the axis during social isolation can alter the mental state (Vitale & Smith, 2022a). Furthermore, overactivation can occur when combined with the maladaptive cycle proposed by Capcioppo's evolutionary theory, leading to overreactions of stress compared to reality.
fMRI Findings
When consulting fMRI findings comparing brain activities between lonely and non-lonely individuals, significant reaction disparities convey the previous concepts of prediction and self-preservatory actions. In a study conducted at the University of Chicago's Center for Cognitive and Social Neuroscience, 23 undergraduate females were monitored while viewing a series of pictures tied to a variety of emotions along with social/nonsocial content. They found that lonely individuals show less fMRI activity when viewing social images of strangers but more when viewing close others. Theoretically, this is an adaptive process signaling the individual to preserve the existing social relationship, furthering the maladaptive hypervigilance and defensiveness. Additionally, lonely individuals report decreased fMRI activity in regions involved in emotional processing, such as the amygdala and nucleus accumbens, during an interpersonal trust game (Cacioppo et al., 2009). The detrimental effects on trust and empathy further harmful effects on the lonely individual's social life, ultimately leading to damaged self-esteem and other altered perceptions.
When it comes to an intervention of perceived loneliness, the best course of action should include explaining the maladaptive cognitive processes that lead one to feel that way. Due to the individual's previous bias towards other strategies, such as support and helping them improve objective social elements, talking through the neurobiology behind their actions can often bring a self-reflectiveness to the individual that can enhance their understanding of social interactions. Learning about loneliness, both the signs in others and oneself can create a safer and less stigmatized mental health environment that can be applied in every community.
References
Barrett, L. F., & Simmons, W. K. (2015). Interoceptive predictions in the brain. Nature reviews. Neuroscience, 16(7), 419–429. https://doi.org/10.1038/nrn3950
Cacioppo, J. T., Norris, C. J., Decety, J., Monteleone, G., & Nusbaum, H. (2009). 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. https://doi.org/10.1162/jocn.2009.21007
Cacioppo, S., Balogh, S., & Cacioppo, J. T. (2015). Implicit attention to negative social, in contrast to nonsocial, words in the Stroop task differs between individuals high and low in loneliness: Evidence from event-related brain microstates. Cortex; a journal devoted to the study of the nervous system and behavior, 70, 213–233. https://doi.org/10.1016/j.cortex.2015.05.032
Finley, A. J., & Schaefer, S. M. (2022). Affective Neuroscience of Loneliness: Potential Mechanisms underlying the Association between Perceived Social Isolation, Health, and Well-Being. Journal of psychiatry and brain science, 7(6), e220011. https://doi.org/10.20900/jpbs.20220011
Vitale, E. M., & Smith, A. S. (2022). Neurobiology of Loneliness, Isolation, and Loss: Integrating Human and Animal Perspectives. Frontiers in behavioral neuroscience, 16, 846315. https://doi.org/10.3389/fnbeh.2022.846315
Vitale, E. M., & Smith, A. S. (2022b). Schematic of proposed insular cortex activity in lonely individuals [Online Image]. Frontiers in behavioral neuroscience. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9029604/figure/F1/
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