The human digestive system is home to a vast community of microorganisms known as the gut microbiome .
According to new research from Michigan State University and the University of North Carolina, Chapel Hill, the gut microbiome was different in babies with strong fear responses and in babies with milder reactions .
To determine whether the gut microbiome was connected to the fear response in humans, a pilot study with approximately 30 babies was designed. The researchers exhaustively selected the cohort to maintain as many factors as possible that impact the gut microbiome. For example, all the children were breastfed and none received antibiotics .
The researchers then characterized the children’s microbiome by analyzing stool samples and assessed a child’s response to fear using a simple test: observing how a child reacted when someone entered the room while wearing a Halloween mask .
Collecting all the data, the researchers observed significant associations between specific characteristics of the gut microbiome and the strength of the babies’ fear responses.
For example, children with uneven microbiomes at one month of age were more fearful at one year of age . Uneven microbiomes are dominated by a small set of bacteria, while even microbiomes are more balanced.
The researchers also found that the content of the microbial community at one year of age was related to responses to fear. Compared with less fearful children, infants with strong responses had more of some types of bacteria and fewer of others.
However, the team did not observe a connection between the children’s gut microbiome and how the children reacted to strangers who did not wear masks.
As part of the study, the team also took pictures of the children’s brains using MRI technology . They thus discovered that the content of the microbial community at one year of age was associated with the size of the amygdala, which is part of the brain involved in making quick decisions about potential threats.