Psilocybin and MDMA reduce costly punishment in the Ultimatum Game

Abstract

Disruptions in social decision-making are becoming evident in many psychiatric conditions. These are studied using paradigms investigating the psychological mechanisms underlying interpersonal interactions, such as the Ultimatum Game (UG). Rejection behaviour in the UG represents altruistic punishment – the costly punishment of norm violators – but the mechanisms underlying it require clarification. To investigate the psychopharmacology of UG behaviour, we carried out two studies with healthy participants, employing serotonergic agonists: psilocybin (open-label, within-participant design, N = 19) and 3,4-methylenedioxymethamphetamine (MDMA; placebo-controlled, double-blind, crossover design, N = 20). We found that both MDMA and psilocybin reduced rejection of unfair offers (odds ratio: 0.57 and 0.42, respectively). The reduction in rejection rate following MDMA was associated with increased prosociality (R2 = 0.26, p = 0.025). In the MDMA study, we investigated third-party decision-making and proposer behaviour. MDMA did not reduce rejection in the third-party condition, but produced an increase in the amount offered to others (Cohen’s d = 0.82). We argue that these compounds altered participants’ conceptualisation of ‘social reward’, placing more emphasis on the direct relationship with interacting partners. With these compounds showing efficacy in drug-assisted psychotherapy, these studies are an important step in the further characterisation of their psychological effects.

MDMA Increases Cooperation and Recruitment of Social Brain Areas When Playing Trustworthy Players in an Iterated Prisoner's Dilemma

“…Emotion recognition and empathy tasks. The Affective Bias task was taken from the EMOTICOM cognitive test battery (Bland et al, 2016) and administered ϳ195 min after dose. In this task, participants see a face appear on the screen for ϳ500 ms and are asked to indicate which emotion the face was expressing from a choice of happy, sad, fear, or anger.…”

“…The outcome measure for affective bias task was the percentage correct for each emotion (fear, anger, happy, sad) and the control condition. Additionally, one can calculate an "affective bias," defined by Bland et al (2016) as the difference between happy and sad emotion accuracy. These outcome measures were compared across experimental sessions using repeated-measures ANOVA, followed by post hoc pairwise comparisons where appropriate.…”

“…Emerging evidence suggests that manipulation of the serotoninergic system affects social decision-making (Wood et al, 2006;Crockett et al, 2010). However, specific assessment of serotonergic manipulation on trust and cooperation in the PD is lacking, with the exception of Wood et al (2006) who reported that acute tryptophan depletion reduced cooperative responses compared with a placebo control condition.…”

“…PD studies have implicated brain regions during feedback, which have been shown to be involved in social processing, including the superior temporal sulcus, temporal-parietal junction, and posterior cingulate gyrus Suzuki et al, 2011). Oxytocin administration altered neural activity when receiving feedback about other players' decisions, with the insula, amygdala, and caudate nucleus being implicated (Rilling et al, 2012;Chen et al, 2017).…”

Foraging Optimally in Social Neuroscience: Computations and Methodological considerations

“…The dACC is often recruited when making social decisions (Gabay et al, 2014;Ruff and Fehr, 2014), and the serotonergic and dopaminergic systems have putatively distinct effects on social behaviours (Crockett et al, 2015;Gabay et al, 2019Gabay et al, , 2018). Yet, the mechanisms underlying these processes have to date still not been fully understood.…”