Research: Gut bacteria affect our social behavior and perception of justice

-
The gut microbiota, a diverse ecosystem of bacteria, viruses and fungi within the digestive tract, plays a crucial role in our health, affecting more than just digestion.

Recent research has revealed the significant impact of our microbiome on cognitive functions, emotions, sense of justice, and even our social behaviors.

According to animal studies, researchers found that mice raised in sterile conditions, devoid of microbial life, show difficulties in social interactions. This finding suggests a deep and fundamental link between gut microbes and social behavior.

However, applying these animal-based findings to human health is complex. Researchers are still exploring the specific neural, immune and hormonal pathways that enable gut microbes to communicate with the brain.

Although a relationship has been observed between gut microbiota composition and fairness, the exact mechanisms remain unclear, leaving scientists to further unravel this complex relationship.

Understanding the relationship between the gut and the brain

Helke Plassmann of the Sorbonne University and INSEAD, who leads the research team at the Paris Brain Institute, sheds light on the possible pathways of this interaction.

“The intestinal ecosystem communicates with the central nervous system through various pathways, including the vagus nerve,” Plassman points out.

This connection may also include biochemical signals that stimulate the release of neurotransmitters such as dopamine and serotonin, which is critical for brain health.

Justice and decision making from the gut

To explore whether the human gut microbiota directly influences decision-making, Plassman and her team turned to the “ultimatum game,” a behavioral test that measures responses to fairness.

In this game, one player splits a sum of money between himself and another player, who can reject the offer if he feels it is unfair, leaving both players with nothing.

This scenario tests “altruistic punishment,” where rejecting an unfair offer promotes equality at the expense of personal gain.

The study included 101 participants, and they were divided into two groups over a period of seven weeks. One group received supplements containing probiotics and prebiotics, while the other group received a placebo. Both groups played an “ultimatum game” at the beginning and end of the study period.

At the conclusion of the study, the supplemented group rejected significantly more inequitable offers, demonstrating enhanced sensitivity to fairness, compared to the placebo group, which showed no change in behavior.

Participants who initially had a bacterial imbalance showed the most pronounced changes in their gut microbiota and higher sensitivity to gut after supplementation.

It is worth noting that these participants also showed decreased levels of tyrosine, a precursor to dopamine, suggesting a possible biological mechanism.

“These new findings highlight the biological pathways we should be looking at,” Plassman says.

The full study was published in the journal PNAS Nexus.