Opioids and social bonding: Effect of naltrexone on feelings of social connection and ventral striatum activity to close others

Inagaki, T. K., Hazlett, L. I., & Andreescu, C. (2019). Opioids and social bonding: Effect of naltrexone on feelings of social connection and ventral striatum activity to close others. Journal of Experimental Psychology: General; http://dx.doi.org/10.1037/xge0000674

Abstract: Close social bonds are critical to immediate and long-term well-being. However, the neurochemical mechanisms by which we remain connected to our closest loved ones are not well understood. Opioids have long been theorized to contribute to social bonding via their actions on the brain. But feelings of social connection toward one’s own close others and direct comparisons of ventral striatum (VS) activity in response to close others and strangers, a neural correlate of social bonding, have not been explored. Therefore, the current clinical trial examined whether opioids causally affect neural and experiential signatures of social bonding. Eighty participants were administered naltrexone (n = 40), an opioid antagonist that blocks natural opioid processing, or placebo (n = 40) before completing a functional MRI scan where they viewed images of their close others and individuals they had not seen before (i.e., strangers). Feelings of social connection to the close others and physical symptoms commonly experienced when taking naltrexone were also collected. In support of hypotheses, naltrexone (vs. placebo) reduced feelings of social connection toward the close others (e.g., family, friends, romantic partners). Furthermore, naltrexone (vs. placebo) reduced left VS activity in response to images of the same close others, but did not alter left VS activity to strangers. Finally, the positive correlation between feelings of connection and VS activity to close others present in the placebo condition was erased by naltrexone. Effects remained after adjusting for physical symptoms. Together, results lend support to theories suggesting that opioids contribute to social bonding, especially with our closest loved ones.