For generations, humans have linked sensations in our gut to our instinct and mood. Now a growing body of science is looking at whether the trillions of microbes, such as bacteria, that live in the gut might be connected to how we feel after all.
A new study, from scientists in Ireland and Finland, has shown that rats who are given microbiome transplants from exuberant human toddlers become more explorative.
Scientists from the University of Turku in Finland and the University of Cork in Ireland focused on studying signs of exuberance to see if the composition of someone’s gut microbiome might impact how they react to things. Exuberance was defined as reacting positively to something and being less likely to withdraw from new or challenging situations.
Faeces samples from exuberant toddlers were transferred to young rats, and the rats were then subjected to a series of tests.
The tests included introducing the rats to new social arenas, allowing them to explore a board with lots of holes in, and a forced swim test. The rats with microbiome from exuberant toddlers seemed more willing to explore new areas, such as poking their heads through more heads on the board.
The authors concluded: “Studies indicate that the gut microbiota composition may be linked to certain temperament traits, defined as biologically-based differences in emotional reactivity and self-regulation.”
Over the past few decades, researchers have been uncovering links between the gut microbiota and our thoughts and behaviour.
One study from 2024 found that rats and mice that had no microbiota, due to being reared in sterile conditions, were more prone to anxiousness and were less sociable than those with microbiota.
“Germ-free” mice have also been found to be more hyperactive and prone to risky behaviour.
In the Finnish-Irish study, researchers wrote: “Animal studies have shown that altering gut microbiota composition by antibiotic or probiotic treatment may result in differences in behavioural profiles”.
There has also been some success in this field on humans. One trial took stool from a healthy donor and transferred it into a patient’s gastrointestinal tract, according to a report in science journal Nature.
The treatment was to try and lessen symptoms of depression, and was successful with some participants.
