Feeling grateful fosters cooperation by synchronizing brain activity between partners

A new study reports that the emotion of gratitude can foster widespread cooperation between individuals, even when it involves a personal cost. The research also reveals that this enhanced cooperation is linked to increased synchronization of brain activity between partners, an effect that appears to grow over time. These results, published in Social Cognitive and Affective Neuroscience, help explain the powerful social function of gratitude in human relationships.

Gratitude is often understood as a positive feeling that arises when one benefits from the kindness of another person. Beyond this personal experience, many researchers consider it an emotion that evolved to help people manage social relationships and work together effectively. It is thought to motivate individuals to reciprocate kind actions and navigate the challenges of cooperation.

A team of researchers from several institutions in Shanghai, China, led by Yangzhuo Li, Junlong Luo, and Xianchun Li, sought to expand on this idea. They noted that past research often examined gratitude in the context of simple, one-time exchanges. The team wanted to explore whether gratitude’s influence extends to different kinds of cooperation and how it might shape interactions as they unfold over time.

To do this, they designed experiments to test cooperation in two distinct scenarios. One scenario involved a “costly” decision, where cooperating with a partner meant giving up a chance for a larger personal gain. The other was a “costless” scenario that depended on precise behavioral coordination, where success was a shared outcome with no temptation to betray the other person.

To observe the neural underpinnings of these interactions, the researchers used a technology called functional near-infrared spectroscopy. This non-invasive method involves wearing a cap with sensors to measure blood flow changes in the brain, allowing the team to track brain activity in both participants simultaneously and look for patterns of inter-brain synchronization, a state where two individuals’ brain activity becomes coupled during an interaction.

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The study recruited 93 pairs of female university students who were strangers to one another. Using only female participants helped control for potential gender-based differences in cooperation and emotional expression that have been documented in other studies. The pairs were randomly assigned to one of three groups: gratitude, joy, or neutral. Each pair first participated in an activity designed to induce the target emotion.

In this task, participants allocated a small amount of money over two rounds. In the gratitude group, a participant was led to believe their partner had generously given them a larger share in the second round, accompanied by a kind message. In the joy group, a computer program provided the same monetary benefit, creating a positive feeling without attributing it to the partner. In the neutral group, the computer allocated the money evenly.

After the emotion induction, the pairs played two different cooperation games while their brain activity was recorded. The first game was a version of the Prisoner’s Dilemma, which models costly cooperation. In each of 30 trials, split into two blocks, participants had to privately choose to either “cooperate” with or “defect” against their partner. Cooperating was best for the pair jointly, but defecting offered a larger individual payoff if the partner cooperated.

After the first block of trials, participants received feedback that was manipulated to show that their partner had defected slightly more often than they had. This created a test of whether grateful participants would be more forgiving of a partner’s apparent selfishness.

The behavioral results from this game showed a clear effect of gratitude. Overall, pairs in the gratitude group achieved mutual cooperation more often and had fewer instances of mutual defection compared to the joy and neutral groups. The dynamic nature of this effect became apparent after the manipulated feedback was given. In the second block of trials, participants in the joy and neutral groups became less cooperative.

In contrast, the cooperation rate in the gratitude group remained stable. This suggests that the feeling of gratitude made participants more resilient to their partner’s slight defection and more willing to continue a cooperative relationship. Psychological questionnaires confirmed that participants in the gratitude group reported higher levels of gratitude and trust toward their partner, feelings that were correlated with higher rates of mutual cooperation.

The second game was a button-press task designed to measure costless cooperation through action coordination. In this game, the two participants had to press a button at the exact same time to score points together. Success depended on their ability to synchronize their actions based on feedback from previous trials.

Here again, gratitude appeared to promote better performance. The gratitude group showed a higher rate of effective adjustment, meaning they were more successful at using feedback to coordinate their timing with their partner. Their overall success rate at winning points also improved significantly from the first block of trials to the second. While the joy group also showed improvement over time, the gratitude group’s performance was generally higher, especially in the second block.

The brain imaging data offered a potential explanation for these behavioral patterns. During the Prisoner’s Dilemma game, the gratitude group showed higher inter-brain synchronization than the joy group in a brain region known as the right middle frontal gyrus, particularly during the second block of trials after the negative feedback. This region is associated with understanding others’ perspectives and adapting one’s behavior in social contexts. The effect was even more pronounced during the button-press coordination game.

The gratitude group exhibited significantly higher brain synchronization in several areas, including the left and right middle frontal gyrus and the right sensorimotor cortex, a region involved in planning and executing physical actions.

A dynamic pattern also emerged in the brain data. For the gratitude group playing the coordination game, inter-brain synchronization in several key areas, including the frontal and temporal regions of the brain, increased from the first block to the second. This progressive neural coupling mirrored their improving behavioral performance.

This connection between brain and behavior was also evident in the finding that higher synchronization in the right middle frontal gyrus was associated with a greater rate of effective adjustment in the button-press game. The brain synchronization was confirmed to be a result of the live interaction, as it was significantly higher in real pairs compared to randomly generated “pseudo-pairs” of participants who did not interact.

The researchers note some limitations of their work. The study involved only young female adults, so the findings may not apply to men, mixed-gender pairs, or people of different ages. The experiments were also conducted using computer-based tasks in a controlled laboratory setting, which may not fully capture the complexity of cooperation in real-world scenarios.

Future research could explore these dynamics in different demographic groups and more naturalistic settings. It could also examine the opposite of gratitude to understand how ingratitude might disrupt cooperative relationships.

The study, “Gratitude enhances widespread dynamic cooperation and inter-brain synchronization in females,” was authored by Yangzhuo Li, Xinyu Cheng, Wanqiu Na, Junlong Luo, and Xianchun Li.