Oxytocin Task

We adapted an iterative version of the Trust Game (King-Casas et al., 2005). During each scan (OT and PL), the subject (“Investor”) played 20 rounds with the same opponent (“Trustee”). At the start of each round, the subject was given 20 monetary units (MU) and told to invest any amount between 0 and 20 with the Trustee. This invested amount was then tripled. The Trustee then repaid some portion of the total (0–60 MU) back to the Investor. While, in reality, the ‘Trustee’ was a computer-generated algorithm, subjects were told they were playing with a human; the deception was revealed following completion of the study. During our debriefing, prior to revealing the deception, we asked subjects about their perception of the game. None of the subjects showed evidence of questioning the cover story. To ensure that the ‘Trustee’ algorithm mimicked human behavior, parameters were estimated from data (N ¼ 48) obtained from a previous study (King-Casas et al., 2005); randomness was set at 10%. Each round consisted of a cue to invest (I1), investment period (I2), delay, investment reveal (I3), delay, cue to repay (R1), repayment period (R2), delay, repayment reveal (R3), delay, totals reveal, and inter-round delay. Delay periods were jittered between 2 and 7 seconds.