Abstract

Infant Gut Microbiome Associated with Cortisol Reactivity and Fear Behavior

Most of the existing research on relationships between the microbiome and hormonal and behavioral responses to painful or frightening stimuli have been carried out in animals. These studies reveal that the gut microbiome causally impacts cortisol reactivity, fear behavior, and the development of fear-related structures in the brain including the amygdala, hippocampus, and medial prefrontal cortex. This presentation will focus on a study which examined similar relationships in human infants using robust, laboratory-based tests and state-of-the-art neuroimaging. Participants include 34 healthy infants from central North Carolina, carefully selected to control for common confounding variables in infant microbiome studies. We found that α-diversity at 1 month of age was strongly associated with concurrent HPA axis reactivity to a heel prick and with greater fear reactivity when viewing Halloween masks at 12 months of age. Features of the 12-month microbiome were also associated with concurrent fear reactivity. Specifically, infants with high levels of Bacteroides and low levels of Veillonella, Dialister, Bifidobacterium, Lactobacillus, and an unnamed genus of Clostridiales showed decreased fear reactivity during the mask task. We also found nominally significant associations between β-diversity measures and volumes of amygdala and medial prefrontal cortex. Our study suggests that the human gut microbiome influences an amygdala-based system which responds to immediate threats, mirroring earlier studies in experimental animals.