31-07-2025
Just Seeing A (Fake) Sick Person Can Activate Your Immune System
We have all experienced the phenomena of seeing a disturbing or disgusting image that makes us feel physically ill. When the human brain processes certain types of visual images, it can send neural signals to our bodies that result in us feeling nauseated, light-headed, or shaky.
Scientists have now learned that certain types of visual imagery can also turn on our immune systems, even without being physically exposed to an infectious agent.
A team of scientists based in Switzerland performed an experiment with 248 healthy adults, in which the subjects were exposed to avatar images of people walking towards them. Some looked healthy with neutral facial expressions, others looked healthy but with fearful expressions, and some looked like they had a contagious illness (indicated by coughing and skin rashes). The subjects wore gaming headsets that created an immersive 3-D virtual reality environment, in which the simulated avatars walked towards them.
When the subjects were approached by avatars who looked sick and appeared ready to invade their personal space, the researcher found that subjects activated their innate lymphoid cells, which is part of the 'first responder' arm of the immune system. This was measured by blood sampling of the subjects. In contrast, this cellular response did not occur when the subjects were approached by fearful-looking but non-infected avatars, or by avatars with neutral expressions.
In other words, although the test subjects were not exposed to any actual infectious agents, the possibility of a simulated contact with an infected person was enough to trigger a real-world immune response. The fact that this response was elicted only by the 'infected' avatars but not the 'fearful' avatars, suggests that this is a specific response to potential infection, as opposed to a generalized response to a generic threat.
The researchers also showed that innate lymphoid cell response caused by simulated exposure to the infected avatars was the same as the response to real-world exposure to flu vaccine (which works by triggering an immune response).
The researchers also used functional MRI (fMRI) analysis of brain activation during the simulated exposures, to determine how the brain processed this simulated threat. They found that the simulated exposure increased blood flow in specific portions of the brain known as the 'salience network' which is 'an ensemble of interconnected brain regions whose major role is detecting and filtering salient stimuli, including threats.'
The exact mechanism by which the brain then activated the immune system is not fully understood, but likely related to stimulation of the hypothalamic–pituitary–adrenal cortex (HPA) axis.
From an evolutionary perspective, these results make sense. Being able to anticipate an imminent threat of infection (and act accordingly) would be a pro-survival trait. And if avoidance of an imminent infection isn't always possible, being able to proactively stimulate the immune system before actual contact with a pathogen could offer a survival advantage vs. activating the immune system only after physical contact.
The authors also noted that this is an example of the 'smoke detector principle' in biological defenses, which is tuned to be mildly oversensitive to threats. In many contexts, an overly sensitive smoke detector that generated a few occasional false-positives (even if there was no actual fire) might save more lives than an insufficiently sensitive smoke detector that generated too many false negatives (failing to respond to actual fires.) The same applies to biological defenses.
This work is very preliminary. But this innovative research sheds light on hitherto unrecognized connections between the brain and the immune system, which could be helpful in developing new treatments against various pathogens. Could appropriate visual imagery help activate the immune system against infections in a way that supplements standard antibiotic therapy? Or stimulate the appropriate immune response to fight cancer cells? I look forward to further investigations along these lines.
