Liu Chao’s research group published a paper in PLOS Biology to reveal the neural computational mechanism of acute stress reversal of third-party intervention in altruistic behavior

On May 16, 2024, Liu Chao’s group at the State Key Laboratory of Cognitive Neuroscience and Learning, Beijing Normal University, IDG/McGovern Institute for Brain Science, published their research in PLOS Biology, “Acute stress during witnessing injustice shifts third-party interventions from punishing the perpetrator to helping the victim”. The study used MRI technology to elucidate the brain and computational mechanism of reversing third-party interventions of altruistic behavior from punishing the transgressor to helping the victim during acute stress, and the research results can help to understand how human beings adopt pro-social behaviors.

Fairness and equity are the basis for building social trust and cooperation. However, inequity affects social harmony and sustainable development. A sense of fairness is an evolutionary achievement, and humans and other primates have evolved to understand the benefits of controlling self-interest and reputation building in the context of resource allocation, and to actively defend fairness and resist unfairness, thereby satisfying the need for continued cooperation and maintaining good social order. When faced with social injustice, even from a third-party perspective, there is still a strong tendency to sacrifice self-interest in order to restore social justice, so-called “heroic” behavior, and among these courageous choices, third-party punishment and third-party helping behavior have been emphasized. However, the choice of behavior and the intensity of participation depends on the situation, and the individual’s acute stress reaction is an important factor, as resistance to injustice is often accompanied by a strong individual acute stress reaction.

Over the past two decades, it has become widely accepted in the neuroscience community that fairness motivation may involve two complementary pathways, a fast, heuristic pathway, often with emotional arousal, and a slower, reasoning-based pathway characterized by cognitive thinking. In contrast, research suggests that exposure to uncontrollable stressful events early on may shift brain functioning from a thoughtful mode to a more rapid, reflexive response mode regulated by primitive neural circuits, but later in the stress period this mode gradually reverts to a state dominated by higher cognitive functions. This stress-sensitive neural system partially overlaps with functional brain networks involved in decision-making related to equitable recovery processes, for example, those related to third-party punishment or helping decisions. However, there is no consensus on the ways in which acute stress intervenes in people’s response to unfair events. For example, previous research has found that people subjected to acute physical stress are more likely to choose third-party punishment when confronted with a moderate degree of unfairness between two other parties unrelated to them, when third-party punishment is in conflict with helping behavior (i.e., when participants can only practically impose one option for restoring fairness in a single interaction) (Wang Huagen et al., 2020). However, in the next study, it was found that when subjected to acute social stress, in the same single interaction, participants exhibited a higher propensity for third-party help in the extreme unfairness condition (Zhen Zhen et al., 2021). However, the intensity of the physiological response resulting from different types of stress elicitation varies, and it was found that acute social stress triggered a greater degree of slow HPA axis response, manifested by higher levels of cortisol release. Cortisol is able to cross the blood-brain barrier and enter the brain, where it further affects brain function by binding to glucocorticoid receptors and salocorticoid receptors (mainly located in the prefrontal cortex and limbic system). However, social stress itself, because of its “social” nature, can also have an impact on further social tasks. Therefore, keeping participants under physical stress conditions for longer periods of time with higher cortisol levels to complete decision-making processes is one of the better options for studying the effects of stress on third-party interventions. Understanding these context-dependent behavioral patterns is a central issue in many fields, including law and politics, economics, and psychology.

Based on this, the researchers induced higher negative emotions, heart rate levels, and higher cortisol responses in participants through a cold pressor paradigm (CPT). Participants witnessed the unfair distribution event of the other two parties multiple times in the MRI environment and provided their own choice preference and intervention intensity (how many tokens were sacrificed to punish or help, respectively) among three choices: third-party punishment, third-party helping, and not participating. The researcher then parsed the participants’ mental computational mechanisms during the decision-making process through a computational modeling approach.

It was found that, at the behavioral level, stress caused third parties to decrease their willingness to punish the transgressor and the severity of the punishment during multiple rounds of interaction, but increased their willingness to help the victim. These findings support tend & befriend theory, suggesting that stressed individuals have stronger altruistic and other-oriented tendencies. Using computational modeling, we further simulated the process of how participants integrate value utilities when making fair recoveries and assign different psychological weights and subjective preferences when allocating amounts to punish transgressors and help victims. We found that when people performed subjective value utility calculations in stressful situations, they used their psychological preferences more for deciding how to help victims than how to punish transgressors.

At the neural level, stress-induced shifts in third-party tendencies from punishing to helping are mediated by influencing emotional salience, central executive, and theory of mind networks. It is characterized by stress-induced increases in amygdala activity and connections to the ventral medial prefrontal, and the need to call for higher activity in dorsolateral prefrontal, temporoparietal coalition, and posterior cingulate regions during punishment, whereas the choice of helping behaviors in multiple rounds of interactions may initiate an “energy-saving mode”.

In general, the study uses computational modeling and neuroimaging techniques to elucidate the mechanisms behind stress reshaping third-party decision-making behavior by redistributing value calculations and neural resources in emotional, executive, and psychological networks to suppress punishment bias.

Dr. Wang Huagen, a PhD student of Chao Liu’s group, was the first author of this study, and Prof. Chao Liu and Prof. Shaozheng Qin were the co-corresponding authors. This research was supported by the National Natural Science Foundation of China (32271092, 32130045), the Science and Technology Innovation 2030 – “Brain Science and Brain-like Research” Major Program (2021ZD0200500), and the National Social Science Foundation of China Major Program (19ZDA363).

Link to paper

Wang H, Wu X, Xu J, Zhu R, Zhang S, Xu Z, et al. (2024) Acute stress during witnessing injustice shifts third-party interventions from punishing the perpetrator to helping the victim. PLoS Biol 22(4): e3002195. https://doi.org/ 10.1371/journal.pbio.3002195

Lab Links

Liu Chao’lab: https://liuchaolab.bnu.edu.cn/ 

Previous Related Papers

Jin K, Wu J, Zhang R, Zhang S, Wu X, Wu T, Gu R, Liu C. Observing heroic behavior and its influencing factors in immersive virtual environments. Proc Natl Acad Sci U S A. 2024 Apr 23;121(17):e2314590121.

Wang, H., Zhen, Z., Zhu, R., Yu, B., Qin, S., & Liu, C. (2022). Help or punishment: acute stress moderates basal testosterone’s association with prosocial behavior. Stress, 25(1), 179-188.

Zhen, Z, Wang, H., Zhu, R., Zhang, S, Jin T, Qin, S., Liu, C. (2021). Acute psychosocial stress increases third-party helping but not punishing behavior. Stress 24 (4), 430-441.

Wang, H., Zhen, Z., Liu, C., & Qin, S. (2020). Punishing or helping: The influence of acute stress on third-party decision-making. Chinese Science Bulletin, 65, 1975-1984.

ZHEN Zhen; QIN Shaozheng; ZHU Ruida; FENG Chunliang; LIU Chao. Neural mechanism of stress and social decision making under acute stress[J]. Journal of Beijing Normal University(Natural Science), 2017, 53(3): 372-378. DOI: 10.16360/ j.cnki.jbnuns.2017.03.020