Beneath the brain's outermost membrane, it turns out, the gut has been quietly posting sentinels. A study in Nature Neuroscience reveals that intestinal infections dispatch specialized immune cells to the dura mater, where they settle as long-lived memory populations capable of recognizing and responding to pathogens that later threaten the central nervous system. This gut-to-brain immune relay, governed by a precise molecular signaling axis, suggests that the body's defenses are more geographically coordinated than previously understood — and that the history of what the gut has survived may