When it comes to fear, babies trust their gut instincts, researchers prove
Why do some babies react to perceived danger more than others? According to new research from Michigan State University (MSU) and the University of North Carolina, Chapel Hill, part of the answer may be found in a surprising place: an infant’s digestive system.
Gut microbiomes in infants could contain clues to help monitor and support healthy neurological development, the researchers said, after their research supported them to learn that the gut microbiome was different in infants with strong fear responses and infants with milder reactions.
Fear responses in early life can be indicators of future mental health, and there is a growing body of research which links neurological well-being to the microbiome in the gut.
The new findings suggest that the gut microbiome could one day provide researchers and physicians with a new tool to monitor and support healthy neurological development.
“This early developmental period is a time of tremendous opportunity for promoting healthy brain development,” said MSU’s Rebecca Knickmeyer, leader of the new study. “The microbiome is an exciting new target that can be potentially used for that.”
Studies of this connection and its role in fear response in animals led Associate Professor Knickmeyer and her team to look for something similar in humans.
“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,” she explained. “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.”
In contrast those children with “exceptionally muted” fear responses may go on to develop callous, unemotional traits associated with antisocial behavior, the Associate Professor added.
To determine whether the gut microbiome was connected to fear response in humans, researchers designed a pilot study with about 30 infants. The researchers selected the cohort carefully to keep as many factors impacting the gut microbiome as consistent as possible. For example, all of the children were breastfed and none was on antibiotics.
Researchers then characterized the children’s microbiome by analyzing stool samples and assessed a child’s fear response using a simple test: observing how a child reacted to someone entering the room while wearing a Halloween mask.
Compiling all the data, the researchers saw significant associations between specific features of the gut microbiome and the strength of infant 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, whereas even microbiomes are more balanced.
The researchers also discovered that the content of the microbial community at one year of age related to fear responses. Compared with less fearful children, infants with heightened responses had more of some types of bacteria and less of others.
The team, however, did not observe a connection between the children’s gut microbiome and how the children reacted to strangers who weren’t wearing masks. Associate Professor Knickmeyer said this is likely due to the different parts of the brain involved with processing potentially frightening situations.
“With strangers, there is a social element. So children may have a social wariness, but they don’t see strangers as immediate threats,” she explained. “When children see a mask, they don’t see it as social. It goes into that quick-and-dirty assessment part of the brain.”
As part of the study, the team also imaged the children’s brains using MRI technology. They found that the content of the microbial community at one year was associated with the size of the amygdala, which is part of the brain involved in making quick decisions about potential threats.
Connecting the dots suggests that the microbiome may influence how the amygdala develops and operates. That’s one of many interesting possibilities uncovered by this new study, which the team is currently working to replicate. Associate Professor Knickmeyer is also preparing to start up new lines of inquiry with new collaborations at IQ, asking new questions that she’s excited to answer.
“We have a great opportunity to support neurological health early on,” she said. “Our long-term goal is that we’ll learn what we can do to foster healthy growth and development.”
The study was recently published in the journal Nature Communications and may be accessed here.