The human microbiome does not only affect our health, but also our behavior. A recent study carried out by a US research team, and published in the latest issue of the journal Nature Communication, suggests that this impact goes back to our earliest moments.
Scientists from Michigan have found that even the fear response in infants could be partially determined by the makeup of bacteria living inside the human gut. They found babies with less balanced gut microbiomes – reflecting greater abundances of certain bacteria in the gut – tended to show increased fear behavior in an experiment, as compared to infants whose gut bacteria were more balanced overall.
In the experiment, a group of over 30 babies (each aged about one year old) had their fear response analyzed when a researcher wore a series of Halloween-style masks in front of them, including a horse mask, a monkey mask, and an alien mask. For each child, their facial fear, vocal distress, bodily fear, escape behavior, and startle response were rated. Interestingly, after the analysis of the infants' stool samples, a link was found between the makeup of their gut microbiome and their fear levels in the mask experiment.
"Not that there's anything necessarily wrong with the fear response of these very young study participants. Fear reactions are a normal part of child development. Children should be aware of threats in their environment and be ready to respond to them. But if they can't dampen that response when they're safe, they may be at heightened risk to develop anxiety and depression later on in life," explains senior author and neuroscientist Rebecca Knickmeyer from Michigan State University, in a report posted on the Science Alert website.
As for how and why gut microbiome distribution might affect levels of fear response like this, the researchers say they need further research.
A former study offered some support evidence to suggest that the volume of the amygdala (which processes fear in the brain, in addition to other emotional responses) at one year of age might also be tied to microbiome composition.