The gut microbiome may play a role in shaping our personality

The rats were given guts microbiome transplants from energetic human babies appear to be more willing to explore their environment. This discovery hints that the bacteria that inhabit our gut during childhood play a role in shaping our personality.

“This suggests that our microbes are active participants in emotional development, rather than just passive passengers,” says Harriet Schellekens at University College Cork in Ireland, who was not involved in the study.

There is a growing body of research linking the microbial communities that live in our gut to our bodies. health, emotions and mood. For example, people who lack certain types of gut bacteria are at higher risk depression or anxiety.

It's not entirely clear whether bacteria are causing these changes or whether the microbial community is changing as a result of behavior, but there are some indications that changing microbiome composition may influence mood. For example, transplanting feces from depressed people into rats. seems to cause depressive behavior in rodents and depressed humans receiving fecal transplants, their symptoms have improved in preliminary tests.

To shed more light on how the gut microbiome may be linked to temperament, Anna Aatsinki from the University of Turku in Finland and her colleagues transplanted feces from babies into young rats.

The team first assessed the personalities of 27 2.5-year-olds using a standard temperament assessment and an exercise in which the children played with a bubble gun.

“We couldn't really study things like anxiety disorders in two-year-olds, but we thought there might be differences in behavior that we could look at; for example, if they are behaviorally inhibited compared to those who are very outgoing and extroverted,” says Aatsinki.

Based on these ratings, the researchers rated 10 of the kids as energetic and eight as inhibited and introverted. From these groups, they selected four energetic and four slow kids—half boys, half girls—and collected samples of their feces.

Glycerol-supplemented fecal samples or glycerol control samples were transferred to 53 22- or 23-day-old rats that had already undergone intestinal cleansing.

Aatsinki and her colleagues then subjected the rats to a series of behavioral tests in different situations. They found that rats with microbiomes of babies high in abundance traits exhibited more exploratory behavior than rats with a control transplant or rats fed feces from inhibited babies.

To study how gut microbes might exert their influence on the brain, the researchers also analyzed rat brain tissue, looking for changes in gene activity. It showed that rats that received transplants from inhibited toddlers had less activity in neurons that produce dopamine, a brain chemical associated with reward for risky behavior.

“This study provides excellent insight into how the gut microbiome may contribute to behavioral tendencies early in life,” says Schellekens. “By transferring microbiota from children to rodents, researchers are creating a rare translational link between microbes, human temperament and brain function.”

“This points to a gut-brain connection that influences curiosity, reward and motivation through the dopamine system,” says Schellekens.

However, the impact should not be overestimated, says Aatsinki. “In general, adult temperamental traits are relatively highly correlated with genetics, but environmental factors, potentially including the microbiome, may influence variation in some behaviors.”

Whether germs are responsible for differences in children's behavior remains an open question, Aatsinki adds. It's also possible that children who develop rambunctious phenotypes interact differently with their environment and new foods and thus develop a different microbiome, she says.