Neural mechanisms of costly helping in the general population and mirror-pain synesthetes

Abstract

Helping others often comes with a cost to ourselves. It has been argued that experiencing the pain of others motivates helping. Here we investigate how individuals that report somatically feeling the pain of others (mirror-pain synesthetes) differ from those that do not, when deciding to help and reduce someones pain conveyed through different modalities. Mirror-pain synesthetes and participants who do not report such everyday life experiences witnessed a confederate expressing pain and could decide to reduce the intensity by donating money. Measuring brain activity using fMRI confirmed our initial hypothesis: self-reported mirror-pain synesthetes increased their donation more steeply, as the intensity of the observed pain increased, and their somatosensory brain activity (in SII and the adjacent IPL) activity was more tightly associated with donation when the pain of other was conveyed by the reactions of the pain-receiving hand. For all participants, in a condition where the pain was conveyed by facial expressions, activation in insula, SII and MCC correlated with the trial by trial donation made, while SI and MTG activation was correlated with the donation in the Hand condition. These results further inform us about the role of empathy in costly helping, the underlying neural mechanism, and individual variability.