The human brain can detect diseases in other people even before they manifest—individuals can, thus, better avoid infection, suggests a new study published in the Proceedings of the National Academy of Sciences.
Humans are endowed with a brain that comes with great faculties. The organ now appears to be even better at detecting and avoiding disease than scientists have previously assumed. A new study conducted by researchers from Karolinska Institutet, Sweden, shows how our vision and smell can help us sense that someone is sick even before the disease manifests itself—this information is then used to avoid those who are ill.
We already have an advanced immune system that helps us fight diseases effectively. However, this means that a fair amount of energy has to be spent to do the job, and prevention is always better than cure. Therefore, avoiding disease in the first place is preferable—and, this is actually what the human brain does when it identifies people with early-stage diseases.
“The study shows us that the human brain is actually very good at discovering this and that this discovery motivates avoidance behaviour,” says lead researcher, Mats Olsson.
Olsson and his team stimulated the immune system of participants with harmless bacteria. This led to the typical symptoms of disease, such as fatigue, pain, and fever. When the disease was developing, the researchers took smell samples from the volunteers who were also photographed and filmed. After a few hours, the injected bacterial substance wore off, and the symptoms disappeared.
The smell samples and images were brought to another group of participants. The latter were also exposed to similar samples coming from healthy people. They, then, had to rate how much they liked the different people, and they also had to identify anyone who appeared to be sick, and which ones they considered attractive, and which ones they would want be open to socialise with; their brain activities were monitored meanwhile.
The findings show that people would prefer socialising with healthy people instead of those who are sick with an artificially-activated immune system—a difference deemed significant, explains Olsson. Furthermore, the brain was found to be good at understanding signals from the senses pertaining to the health of others. The authors, thus, conclude that survival and avoiding infection are naturally linked.
So, the immune system does not work alone. Rather, the brain has its own way of keeping diseases at bay—and, when this works, the immune system does not even need to be activated, given that contact with diseased people is avoided, and no infection occurs. However, this behaviour will not always be triggered. Consider a parent whose child has the flu: the former will, instead, care for the sick person even more.
“Common sense tells us that there should be a basic behavioural repertoire that assists the immune system. 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.”