Our need to experience intimate social connection, warm care, and social comfort persists throughout life: from our first to final days. Despite widespread appreciation for the importance of social connection for health and well-being, we lack a complete understanding of how we fulfill our social connection needs and the neurobiological pathways that link social connection with health. My program of research, therefore, tackles two interrelated questions: (1) what neurobiological pathways contribute to social connection with the people with whom we are closest? (2) how does social connection, or a lack thereof, affect physical and mental health? I test these questions from the theoretical perspective that social connection is fundamental to our everyday functioning. Therefore, the affective experience from connecting with others may be supported by the same ‘basic’ biological systems that also keep the body functioning. We approach our research from the perspective that emotional experience arises from physical, bodily experience. Specifically, feelings of social connection arise from afferent connections that bring the physiological condition of the body to the brain (i.e., a ‘bottom-up’ process). Feelings of connection then feedback ‘down’ to the body to ultimately affect health. Therefore, we utilize methods from pharmacology, neuroscience, psychophysiology, and experimental social psychology to assess how changes to the body causally affect the mind and conversely, how changes to the mind causally affect the body.

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). 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 mediates 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.

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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). 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 et al., 2018), normal variation in body temperature (Inagaki & Human, 2019), and connectivity of a subsystem of the brain at rest (Inagaki & Meyer, 2019) 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 we give to 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, 2017 Current 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 giving support behavior and also (b) reduce social withdrawal or stress-related responding to facilitate effective care during times of need.

In support of our theoretical model, we have shown that giving support to others activates brain regions associated with maternal caregiving behavior in animals that also serve to reinforce such behavior (Inagaki & Eisenberger, 2012; Inagaki et al., 2016; Inagaki & Ross, 2018, all published in Psychosomatic Medicine). Further, we have shown that giving support to others (vs. a neutral control condition) leads to reduced sympathetic nervous system responding to a social stressor (Inagaki & Eisenberger, 2016, Psychophysiology) and is associated with reduced stress-related neural responding. Collectively, this line of research suggests that an unintended 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.