Skip to main content

Or 34,00 After 66% tax deduction

I make a monthly donation I make an IFI donation
Research, science & health

The composition of the gut microbiota could influence decision-making

Published on: 16/05/2024 Reading time: 1 min
Population de bactéries commensales (en rouge) dans un intestin grêle de souris. Crédit : University of Chicago

The way we make decisions in a social context can be explained by psychological, social, and political factors. But what if other forces were at work? Hilke Plassmann and her colleagues from the Paris Brain Institute and the University of Bonn show that changes in gut microbiota can influence our sensitivity to fairness and how we treat others. Their findings are published in the journal PNAS Nexus.

The intestinal microbiota—i.e. all the bacteria, viruses and fungi that inhabit our digestive tract—plays a pivotal role in our bodies, well beyond digestive function. Recent research underscores its impact on cognition, stress, anxiety, depressive symptoms, and behaviour; mice raised in a sterile environment, for example, have difficulty interacting with other individuals.

While these findings are promising, most of this research is carried out on animals and cannot be extrapolated to humans. Nor does it allow us to understand what neuronal, immune, or hormonal mechanisms are at work in this fascinating dialogue between brain and intestine: researchers observe a link between the composition of the microbiota and social skills but do not know precisely how one controls the other.

The available data suggests that the intestinal ecosystem communicates with the central nervous system via various pathways,including the vagus nerve. It might also use biochemical signals that trigger the release of neurotransmitters, such as dopamine and serotonin, which are essential for proper brain function.

Hilke Plassmann (Sorbonne University, Insead), head of the Control-Interoception-Attention Team at the Paris Brain Institute, and professor at Insead.

Studying altruistic punishment


To determine whether the composition of the human gut microbiota could influence decision-making in a social setting, the researcher and her colleagues used behavioural tests— including the famous “ultimatum game” in which one player is given a sum of money he must split (fairly or unfairly) with a second player, who is free to decline the offer if she deems it insufficient. In that case, neither player receives any money.

Refusing the sum of money is equivalent to what we call “altruistic punishment,” i.e. the impulse to punish others when a situation is perceived as unfair: for the second player, restoring equality (no one receives any money) sometimes feels more important than obtaining a reward. The ultimatum game is then used as an experimental way of measuring sensitivity to fairness.

To fully exploit this effect, the researchers recruited 101 participants. For seven weeks, 51 took dietary supplements containing probiotics (beneficial bacteria) and prebiotics (nutrients that promote the colonization of bacteria in the gut), while 50 others received a placebo. They all participated in an ultimatum game during two sessions at the beginning and end of the supplementation period.

 

Are bacteria pulling the strings?


The study’s results indicate that the group that received the supplements was much more inclined to reject unequal offers at the end of the seven weeks, even when the money split was slightly unbalanced. Conversely, the placebo group behaved similarly during the first and second test sessions.

Moreover, the behavioural change in the supplemented group was accompanied by biological changes: the participants who, at the start of the study, had the greatest imbalance between the two types of bacteria that dominate the gut flora (Firmicutes and Bacteroidetes) experienced the most significant change in the composition of their gut microbiota with the intake of supplements. In addition, they also showed the greatest sensitivity to fairness during the tests.

The researchers also observed a sharp drop in their levels of tyrosine, a dopamine precursor, after the seven-week intervention. For the first time, a causal mechanism is emerging: the composition of the gut microbiota could influence social behaviour through the precursors of dopamine, a neurotransmitter involved in brain reward mechanisms.

It’s too early to say that gut bacteria can make us less rational and more receptive to social considerations. However, these new results clarify which biological pathways we must look at. The prospect of modulating the gut microbiota through diet to positively influence decision-making is fascinating! We need to explore this avenue very carefully.”

Hilke Plassmann

Funding

The study was funded by the French National Research Agency (ANR), the Health Economics Initiative of the Sorbonne University Alliance, the German Federal Ministry of Education and Research, and the European Research Council (ERC).

Sources

Falkenstein, M. et al. Impact of the Gut Microbiome Composition on Social Decision-Making. PNAS Nexus, May 2024. DOI : 10.1093/pnasnexus/pgae166.

Our news on the subject

Interneurones. Crédit : UCLA Broad Stem Cell Research Center.
Stimulating specific neurons in the striatum stops compulsive behaviour
What if we could resist compulsions? These irrational behaviours, particularly common in obsessive-compulsive disorder (OCD), are hard to suppress. At Paris Brain Institute, Éric Burguière's team shows that we can anticipate them and block them ...
09.10.2024 Research, science & health
Les nerfs moteurs présents dans la moelle épinière se projettent vers la périphérie, où ils entrent en contact avec les muscles, formant des connexions appelées jonctions neuromusculaires. Crédit : James N. Sleigh.
Ultrasound show unexpected effects on motor neuron disease
Over the past fifteen years, neurosurgeons have been perfecting a fascinating technique: using ultrasound to temporarily open the blood-brain barrier to facilitate the action of therapeutic molecules in the central nervous system. At Paris Brain ...
09.05.2024 Research, science & health
Un neurone
Rett syndrome: a new gene therapy on the way
Gene therapy could be our best chance of treating Rett syndrome, a neurological disorder that causes severe intellectual and motor impairments. At Paris Brain Institute, Françoise Piguet and her colleagues have looked closely at brain cholesterol ...
07.16.2024 Research, science & health
Lésions d’un patient à l’inclusion dans le protocole (M0) disparues après 2 ans de traitement à la Leriglitazone (M24)
The dual effect of leriglitazone in X-linked Adrenoleukodystrophy (X-ALD)
In 2023, the team led by Professor Fanny Mochel (AP-HP, Sorbonne University), a Paris brain Institute researcher, showed that daily dose of leriglitazone slow down the progression of myelopathy in patients with X-linked adrenoleukodystrophy, and ...
06.28.2024 Research, science & health
Une tête de statue de l'île de Pâques sur laquelle sont posées des éléctrodes
A multimodal approach to better predict recovery in patients with disorders of consciousness
When a patient is admitted to intensive care due to a disorder of consciousness—such as a coma—establishing their neurological prognosis is a crucial yet challenging task. To reduce the uncertainty that precedes the medical decision, a group of ...
05.30.2024 Research, science & health
Leucodystrophie
New gene therapy for metachromatic leukodystrophy proves effective in mice
Metachromatic leukodystrophy is a rare genetic disorder that mainly affects young children and results in severe neurological symptoms accompanied by a loss of motor and intellectual capacities. At Paris Brain Institute, Françoise Piguet and her ...
04.22.2024 Research, science & health
See all our news