Contrary to how most zombie movies play out, the human brain, while apparently delicious, is actually aces at subconsciously detecting the subtle traces of disease and sickness in others.
Researchers from the Karolinska Institute in Sweden recently discovered that our vision and sense of smell is adequate enough to suss out any sickies around us. The study, which appeared in the journal Proceedings of the National Academy of Sciences, gave participants injections of harmless bacteria that activated their immune systems, which gave them the usual symptoms of sickness like fatigue, aches, and fever; while doing so, the scientists collected some samples, pictures, and videos of their scent.
Then some other people were exposed to the smells and sights, along with some scents and images of healthy controls, and then asked which people looked sick, which they found attractive, and which would they hang out with—all while their brains were scanned by an MRI machine. What they found was that the brain acted different when they smelled or saw the ill people, essentially subtly alerting us to stay away.
"Our study shows a significant difference in how people tend to prefer and be more willing to socialize with healthy people than those who are sick and whose immune system we artificially activated," said lead study author Mats J. Olsson, Ph.D., a professor of psychology at the institute. "We can also see that the brain is good at adding weak signals from multiple senses relating to a person's state of health."
The researchers believe that this shows a biological verification of the argument that in order to survive we will instinctively avoid those who are infected. "Common sense tells us that there should be a basic behavioral repertoire that assists the immune system,” said Olsson. “With this study, we demonstrate that the brain is more sensitive to those signals than we once thought."