We have a basic need to experience intimate social connection, warm care, and social comfort from our first to final days. Despite widespread appreciation for the importance of social connection, scientists lack a complete understanding of how people fulfill and maintain their social connection needs and the pathways that link social connection with health. We approach our research from the theoretical perspective that fulfilled social connection is fundamental to everyday functioning. Therefore, experiences of social connection may be supported by the same systems that regulate other fundamental body functions. Specifically, feelings of social connection arise from pathways that bring the physiological condition of the body to the brain. Feelings of connection then feedback to the body to ultimately affect health. Using methods derived from pharmacology, neuroscience, psychophysiology, and experimental social psychology, we test these bidirectional body-to-mind pathways to further understanding of our most critical social experiences - those we share with family, close friends, and other loved ones.

Opioids and Social Connection:Endogenous opioids, best known for their role in pleasure and pain, are also proposed to influence social connection with close others (Inagaki, 2018,Current Direction in Psychological Science). Despite a long-standing, well-characterized animal literature supporting this possibility, the causal role of opioids to social connection with close others had never been tested in humans. Using a pharmacological challenge to causally manipulate endogenous opioids, my colleagues and I were the first to show that blocking natural opioid processing via naltrexone (vs. placebo) leads to reduced feelings of social connection toward close others both in the lab and in daily reports collected outside of the lab (Inagaki et al., 2015; Inagaki et al., 2016, Ross et al., 2021). Further, we showed that the effects of naltrexone causally affect the brain (Inagaki, et al., 2019a; Inagaki et al., 2019b). Thus, naltrexone (vs. placebo) reduced social connection-related neural activity to close others, and disrupted the link between subjective experience and the brain. Naltrexone did not, however, affect neural responses to strangers, suggesting opioids are particularly relevant for our close social relationships. Findings from this line of work are uncovering one of the basic pathways that mediate close social connections and informs a larger neurobiological model of social connection.

This line of work is generously supported by the Brain & Behavior Research Foundation and the National Institute on Drug Abuse (NIDA).

Social Warmth:Experiences of social connection with others are commonly described as warm. Indeed, terms such as 'warm feelings,' 'warm hearted,' 'warmly received,' and the like abound in writings about social connection dating back to Confucius and the ancient Greeks through to modern day writing. Beyond language, our line of work on 'social warmth' shows that experiences of social connection share similar mechanisms as those that support thermoregulation, the process by which the body monitors and regulates its relatively warm internal temperature (Inagaki & Eisenberger, 2013; Inagaki et al., 2015; Inagaki et al., 2016; Inagaki, Hazlett, & Andreescu, 2019; Inagaki & Human, 2019; Inagaki & Ross, 2020). Together, our research on the overlap between social and physical warmth suggests another route by which we maintain our social connections and fulfill this social need is via warmth.

Brain and body at rest and Social Connection:The body is constantly working to sustain life - the heart beats, blood continues to flow to the brain, and so on. Might these moments of 'rest' where there is no explicit experimental manipulation or task contribute to social connection? Our newest line of work assesses the body and brain at rest as a potential contributor to social connection. Thus, resting (tonic) blood pressure (Inagaki & Gianaros, 2022; Umeda, Leutze, & Inagaki, 2021; Inagaki et al., 2018), normotensive variation in body temperature (Inagaki & Human, 2019), and connectivity of a subsystem of the brain at rest (Inagaki & Meyer, 2019; Inagaki, Brietzke, & Meyer, 2021) predict sensitivity to social connection. This line of work extends our theoretical perspective from experimental manipulations of the body (opioids; warmth) to resting, tonic body responses as potential contributors to social connection.

Giving Social Support:A number of theoretical perspectives highlight the importance of giving to and caring for others for continued relationship maintenance, intimacy, and health. Even so, most research on social support has focused on the benefits of receiving support; largely ignoring effects that come from the support wegiveto others on the individual giving. My theoretical perspective suggests that the neurobiological mechanisms that originally supported the care of infants extend to other forms of support-giving and ultimately, lead to health (Inagaki, 2018,Annals of the NY Academy of Sciences; Inagaki & Orehek, 2017Current Directions in Psychological Science). From this perspective, caring for others is not just the "right thing to do" but is critical to our species' survival. We have proposed that mechanisms are therefore in place to (a) reinforce and motivate support-giving behavior and (b) reduce social withdrawal or stress-related responding to facilitate effective care during times of need. Collectively, this line of research suggests that a benefit of giving may be reducing the giver's own stress and highlights support-giving as an overlooked contributor to how social support can benefit health.

This line of work is generously supported by the National Science Foundation.

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