To investigate the effect of intranasal Oxytocin and L-DOPA's effect on vicarious optimism.

The current study adopted a double-blind, double-dummy, placebo-controlled mixed design, with Treatment (oxytocin, dopamine, and placebo) as a between-subjects factor, and Target (self, friend, and an identifiable stranger) and Feedback (desirable vs. undesirable) as within-subjects factors. Upon arrival, participants first completed a set of questionnaires, including mood measurements and other questionnaires related to optimistic or prosocial tendency. Participants then self-administered with the pharmacological challenge 40 min before the main task, i.e., the belief updating task where participants indicated and updated their beliefs about the future of oneself, a gender-matched best friend, and a gender-matched identifiable stranger. At the end, participants completed the mood measurement again, as well the debriefing questionnaires which designed to measure their beliefs about the experimental process.

For the vicarious optimism task, participants completed three blocks of the two-session belief updating task where they were asked to estimate the likelihood of adverse life events happening to three targets: themselves (referred as Self), a gender-matched best friend (referred as Friend), and an identifiable stranger (whose name, brief description and picture were presented to the participants to get familiar with before the estimation, such as "The stranger is Zhexing, a 25-year-old male, Chinese"; referred as Stranger).

Participants completed two estimation sessions for one target before beginning with the next target, and the order of targets was counterbalanced across participants within each group. For the first session of each target block, participants were first presented with 30 different adverse life events (in a random order) and estimated the likelihood of each event happening to the target in the future (the 1st estimation, referred to as E1) on a self-paced basis. Participants were then presented with the probability of each event occurring to an average person in a similar environment (Feedback) for 2s. In the second session, participants estimated the likelihood of the same 30 events (in a random order) happening to the target person again without receiving feedback (the 2nd estimation, referred to as E2).

Inclusion Criteria:

• healthy subjects without past or current psychiatric or neurological disorders

Exclusion Criteria:

• subjects with past or current psychiatric or neurological disorders

we opted to recruit only males for the present study.