<p>by Kyu-Chan Cho, Won-Jae Lee</p> Microbes are increasingly recognized as modulators of host behavior, but the underlying mechanisms are poorly understood. A new PLOS Biology study reveals a microbiome-to-gut-to-neuron pathway linking developmental microbial exposure to later food avoidance. Microbes are increasingly recognized as modulators of host behavior, but the underlying mechanisms are poorly understood. This Primer discusses a new PLOS Biology study that reveals a microbiome-to-gut-to-neuron pathway linking developmental microbial exposure to later food avoidance.