You’re in a crowded train. Someone nearby sneezes, eyes watery, nose red. You take a step back. That reaction seems to be social conditioning and a learned experience. But it may run deeper than behavior. Now, we know that there may be more going on, according to a new study in Nature Neuroscience. Responses to visible signs of sickness may not be purely behavioral. They may extend to your immune system too.

Researchers in Switzerland and Italy found that simply seeing someone who looks contagious can trigger your brain’s threat circuits and mobilize your immune cells. No actual pathogen is needed to trigger a response, just a visual cue. The team tested this using virtual reality (VR), creating digital avatars that looked sick and watching how people’s bodies responded.

This work is fascinating and so simple that one wonders why no one had thought to do it before. In a series of VR trials, 248 healthy participants watched digital avatars approach their faces. Some looked neutral, some fearful, some showed clear signs of illness like rashes or coughing. Participants responded to mild facial touches faster when a “sick” avatar was nearby, even at a distance. Their brains were already on high alert, subtly expanding the monitored space around the body in response to infection threats.

Brain imaging revealed........

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