Biology subjects

Numano, S.

Publications and source records attributed to Numano, S..

2 recordsLinked to original sources

bioRxiv2025

Overcoming pride via the dorsal ACC underlies acceptance of unfair offers

Bargaining is a fundamental social behavior in which individuals often accept unfair offers. Traditional behavioral models, based solely on choice data, typically interpret this acceptance as simple reward-maximization. However, the suppression of emotions such as inequity aversion or pride may also play a critical role in this decision. Incorporating response time alongside choice data provides a means to quantify participants internal conflict in suppressing these emotions and deciding to accept unfair offers. In this study, we conducted functional magnetic resonance imaging (fMRI) of the ultimatum game, where participants decided within 10 seconds whether to accept or reject monetary distribution offers from a proposer. Using the drift diffusion model (DDM), we quantified decision-making dynamics based on both choice and response time. Participants who suppressed disadvantageous inequity (DI)-driven rejection (reflected by a lower DDM weight for DI) exhibited heightened dorsal anterior cingulate cortex (dACC) activity in response to DI. Functional connectivity analysis revealed a negative correlation between the dACC and the ventrolateral prefrontal cortex (vlPFC) when DI was large, which encoded both the rejection rates, and the response times associated with accepting DI offers. Furthermore, vlPFC activity was significantly correlated with amygdala activity during high DI conditions, specifically encoding response time for accepting DI offers but not rejection rates. Importantly, these findings could not be captured using standard value-based models that rely solely on choice data. Our results underscore the dACCs critical role in mediating the suppression of emotional responses to DI, enabling the acceptance of unfair offers in a dynamic bargaining process.

neuroscience↗

bioRxiv2024

Selfish behavior requires top-down control of prosocial motivation

Individuals must regularly choose between prosocial and proself behaviors. While past neuroscience research has revealed the neural foundations for prosocial behaviors, many studies have oversimplified proself behaviors, viewing them merely as a reward-maximization process. However, recent behavioral evidence suggests that response times for proself behaviors are often slower than those for prosocial behaviors, suggesting a more complex interdependence between prosocial and proself neural computations. To address this issue, we conducted an fMRI experiment with the ultimatum game, where participants were requested to accept (money distributed as proposed) or reject (both sides receive none) offers of money distribution. In the decisions, the participants could maximize self-interest by accepting the offer (i.e., proself), while by rejecting it, they could punish unfair proposers and promote the "equity" social norm (i.e., prosocial). We constructed a drift diffusion model (DDM) that considers both behavioral choices and response times and used the DDM parameters in our fMRI analysis. We observed that participants who suppressed inequity-driven rejection behaviors displayed heightened dACC activity in response to disadvantageous inequity. Importantly, our functional connectivity analysis demonstrated that the dACC exhibited negative functional connectivity with the amygdala when unfair offers were presented. Furthermore, the PPI connectivity encoded the average reaction time for accepting unfair offers (i.e., proself behaviors). Considering that the amygdala also responded to disadvantageous inequity in these experiments and previous studies, these results show that the top-down control of prosocial motives (i.e., aversion to disadvantageous inequity) plays a key role in implementing proself behaviors.

neuroscience↗