For generations, humans have associated gut sensations with instincts and moods. Now, a growing body of science is investigating whether the trillions of microorganisms, like the bacteria that live in our gut, are ultimately linked to how we feel.
A new study by scientists in Ireland and Finland found that mice that received microbiome transplants from active human infants became more exploratory.
Scientists from the University of Turku, Finland, and the University of Cork, Ireland, focused on studying signs of vitality to see if the composition of a person’s gut microbiome could affect the way they react to things. Vitality has been defined as reacting positively to something and being less likely to withdraw from new or challenging situations.
Fecal samples from energetic infants were transferred to young rats and the rats were subjected to a series of tests.
Testing included introducing the rats to a new social area, allowing them to explore a board with many holes, and performing a forced swim test. Mice with the microbiomes of vibrant infants seemed more willing to explore new areas, such as poking their heads through more holes in the board.
The authors concluded: “Research has shown that gut microbiome composition can be associated with specific temperament traits, defined as biologically based differences in emotional reactivity and self-regulation.”
Over the past few decades, researchers have been uncovering links between gut microbes and our thoughts and behavior.
A 2024 study found that rats and mice without microbiota because they were raised in germ-free environments felt more anxious and were less sociable than those with microbiota.
Additionally, “germ-free” mice have been found to be hyperactive and prone to risky behavior.
In the Finland-Ireland study, researchers wrote: “Animal studies have shown that altering the composition of the gut microbiota with antibiotic or probiotic treatment can lead to differences in behavioral profiles.”
There have also been human successes in this field. In one experiment, stool was collected from a healthy donor and transferred into the patient’s gastrointestinal tract, according to a report published in the scientific journal Nature.
The treatment was intended to relieve symptoms of depression and was successful for some participants.
