UCLA

Social connection, the affectively pleasant experience of being close to and bonded with others, is a ubiquitous and critical experience for continued social bonding, immediate and long- term health, and overall well-being. However, for such an important experience, few have experimentally examined the mechanisms by which we connect with others. The strongest insights into social affiliation and bonding come from work in animals showing that the maintenance and monitoring of social relationships rely on many of the same systems that support basic sensory and motivational circuits. With this literature as a starting foundation, the following dissertation aims to examine the neurobiological mechanisms underlying social connection in humans with an emphasis on the specific contributions of thermoregulatory and reward-related systems. To begin, paper 1 examines the potential shared neural mechanisms that contribute to social connection and physical warmth with a sample of 20 participants who read positive, loving messages written by their friends and family and separately, held a warm pack (to increase physical warmth) while lying in the fMRI scanner. Paper 1 revealed, for the first time, that an experience of social connection shares overlapping neural activity with an experience of physical warmth lending support to the description of social affiliation as "heartwarming." Next, in one of the first tests of the brain opioid theory of social attachment in humans, paper 2 pharmacologically manipulated the endogenous opioid system with an opioid- antagonist, naltrexone, to uncover the importance of opioids to feelings of connection both in the laboratory and in the real-world using daily diary assessments. Finally, paper 3 follows up on the results from paper 1 to show that opioids are also involved in the feelings of connection from physical warmth. Collectively, the results from this dissertation add to existing models of social bonding as a basic need on its own and provide a basis for understanding how to help those lacking social connections.