Endogenous opioid receptor system mediates costly altruism in the human brain

Abstract

Functional neuroimaging studies suggest that a large-scale brain network transforms others pain into its vicarious representation in the observer, potentially modulating helping behaviour. The neuromolecular basis of individual differences in vicarious pain and helping, however, have remain poorly understood. Here we investigated the role of the endogenous -opioid receptor (MOR) system - known for its role in analgesia and sociability - in altruistic costly helping. MOR density was measured with high-affinity agonist radioligand [11C]carfentanil. In a separate fMRI experiment, participants could choose to donate money to reduce the pain of the confederate who was subjected to electric shocks of varying intensity. We found that subjects were in general willing to engage in costly helping, and haemodynamic activity in amydala, anterior insula, anterior cingulate cortex, striatum, primary motor cortex, primary somatosensory cortex, and thalamus increased when participants witnessed the pain of others. These haemodynamic responses were negatively associated with MORs availability in the striatolimbic and cortical emotion circuits. In turn, haemodynamic responses during helping were positively associated with MOR availability in the anterior cingulate cortex and hippocampus. Altogether these data suggest that the endogenous MOR system modulates the processing of altruistic behaviour and costly helping in the human brain.