This paper is part of the Research Priority Program ‘Foundations of Human Social Behaviour—Altruism versus Egoism’ at the University of Zurich. We also acknowledge support by the National Center of Competence in Affective Sciences, the Neurochoice Project of SystemsX, and the Swiss National Science Foundation. We thank F. Heusi for her research assistance during the conduct of the experiments.

Author Contributions C.E, E.F., M.H. and M.N. designed research; C.E. and R.S. conducted the experiment; C.E., E.F. and M.N. planned the data analysis; C.E. and M.N. performed data analysis; C.E., E.F., M.H. and M.N. wrote the paper.