The Ultimatum Game and the brain: A meta-analysis of neuroimaging studies

Abstract

Social decision-making tasks involve psychological processes key to effective functioning in a complex, social world. The Ultimatum Game (UG) is a widely studied social decision-making task, which models responses to fairness. A number of neuroimaging studies have investigated the UG to identify neural correlates of unfairness and decisions to reject versus accept an offer. We present the first quantitative summary of neuroimaging studies in social decision-making with a meta-analysis of 11 fMRI studies of the UG, including data from 282 participants. Effect-Size Signed Differential Mapping was used to estimate effect sizes from statistical parametric maps and reported peak information before meta-analysing them. Consistent activations were seen in the anterior insula, anterior cingulate cortex (ACC), supplementary motor area (SMA) and cerebellum in response to unfair offers. Robust activations in the ACC, SMA and putamen were seen when deciding to reject rather than accept UG offers. These are consistent with models of motivational conflict during the UG decision-making process, a response to norm violations, with a possible role for the reward system.

Not on my team: Medial prefrontal cortex responses to ingroup fusion and unfair monetary divisions

“…This contrast revealed a cluster that extended over a large portion of the mPFC (Figure 2), including both the DMPFC (areas 8 and 9) and VMPFC (area 32), in the same region as recently identified within a meta‐analysis of UG studies (Feng et al., 2015; Gabay et al., 2014). This large cluster survived whole brain cluster correction ( p <  0.001 uncorrected voxel‐wise; p  <   0.05 FWE cluster‐correction) at the level recommended in recent analyses of corrections for multiple comparisons (Eklund et al., 2016; Woo et al., 2014).…”

“…Recent meta‐analyses have highlighted that the DMPFC and the Insula are key regions that respond differentially to equitable and inequitable offers in the UG (Feng et al., 2015; Gabay et al., 2014). Similarly, a large number of different paradigms have shown that several regions including both the DMPFC and VMPFC respond to ingroup and outgroup members differently (Cikara & Van Bavel, 2014; Cikara et al., 2014; Harris & Fiske, 2006; Hein et al., 2010; Molenberghs et al., 2016).…”

“…Intriguingly, previous studies have identified that activity in the regions of the DMPFC and VMPFC is increased in response to unfair offers relative to fair offers (Feng et al., 2015; Gabay et al., 2014). Surprisingly, we identified this pattern of activity in these regions but only for offers from ingroup members, not for outgroup or neutral individuals.…”

“…(2015) and Gabay et al. (2014). The peak coordinates from these studies for signaling fairness lie within the masks of areas 8, 9, 32, and 24.…”

“…Studies using such approaches also implicate the mPFC in processing the fairness of other individuals, including when interacting during economic games such as the ultimatum game (UG) (Feng, Luo, & Krueger, 2015; Gabay, Radua, Kempton, & Mehta, 2014; Güth, Schmittberger, & Schwarze, 1982; Koenigs & Tranel, 2007; Sanfey, Rilling, Aronson, Nystrom, & Cohen, 2003). In the UG there are two players – the ‘proposer’ who makes an offer of how to split a pot of money with a ‘responder’.…”