Posted on Jun 05, 2017, 10 a.m.
A team of researchers has found evidence suggesting that our sense of smell and vision create awareness of disease in others before it even breaks out.
A new study conducted by the researchers at Karolinska Institutet in Sweden has concluded that the human brain is much better at discovering and avoiding diseases in their early stages than previously believed. The study was motivated by the theory that people tend to have more positive reactions to people who are healthy than to those who are unwell.
Volunteer participants were selected to prove the feasibility of this study. They were injected with harmless sections of bacteria. These injections stimulated the systemic immune response to the invasion of foreign substances to the body. The participants started to exhibit symptoms of the particular disease which include fatigue, fever and mild levels of pain. During this period of time body odor samples were taken from them and they were photographed and videotaped. The symptoms were only set to manifest for a few hours after the injection, after which point the injected substances disappeared.
A second group of participants were then exposed to the images and smells of these volunteers as well as for those of participants. They were asked to rate how much they liked the study subjects while an MR scanner measured their brain activities. They were also required to make evaluations, based purely by looking at the imagery, declaring which particular participants appeared to be sick, which they deemed to be attractive and which they would consider socializing with. They were less likely to state that they wanted to socialize with those who were sick. The odors from the sick people appeared to cause them to be even less likable to the participants.
The study went ahead to prove that the brain does actually harbor more favorable reactions towards people who are healthy. “Our study shows a significant difference in how people tend to prefer and be more willing to socialise with healthy people than those who are sick and whose immune system we artificially activated,” said Professor Olsson. “We can also see that the brain is good at adding weak signals from multiple senses relating to a person's state of health”. This appears to be biological confirmation that survival naturally involves avoiding infection.
One interesting factor that emerged is that the opposite was witnessed in people who had close relations. "Avoidance, however, does not necessarily apply if you have a close relationship with the person who is ill,” says Professor Olsson. “For instance, there are few people other than your children who you’d kiss when they have a runny nose. In other words, a disease signal can enhance caring behaviour in close relationships. With this study, we demonstrate that the brain is more sensitive to those signals than we once thought.”
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Christina Regenbogen, John Axelsson, Julie Lasselin, Danja K. Porada, Tina Sundelin, Moa G. Peter, Mats Lekander, Johan N. Lundström, Mats J. Olsson. Behavioral and neural correlates to multisensory detection of sick humans. Proceedings of the National Academy of Sciences, 2017; 201617357 DOI: 10.1073/pnas.1617357114