(a) First, we informed the participants that we would send them money for the next 4 weeks (25 Swiss francs per week). We asked half of the participants to commit to spending this money on other people (experimental group) and half of the participants to commit to spending the money on themselves (control group). In addition, we assessed the participants’ subjective happiness upon their arrival at the laboratory (T1), that is, before they had made the commitment, and after scanning, that is, at the end of the experiment (T2). (b) After the participants had made the commitment, they were asked to select one person to whom they wanted to give a present. Then they performed an independent decision-making task in the MRI scanner. In each trial, the participants were presented with an option that they could accept or reject. Each option was a combination of the benefits for the other person and the participants’ own costs. The magnitude of the benefits and costs varied independently and pseudorandomly from 3 to 25 Swiss francs. Each option was displayed for 4 s, which was the maximum response time. The selected response and the option were displayed together until the jittered ITI began. The participants responded by pressing the left or right arrow button, which corresponded to the ‘yes’ (accept) or ‘no’ (reject) displayed on the screen. The mapping between ‘yes’ or ‘no’ and left or right arrow buttons was randomized across trials.