Visual cues of respiratory contagion: Their impact on neuroimmune activation and mucosal immune responses in humans

Abstract

This study investigated the neural correlates of perceiving visual contagion cues characteristic of respiratory infections through functional magnetic resonance imaging (fMRI). Sixty-two participants (32f/ 30 m; ∼25 years on average) watched short videos depicting either contagious or non-contagious everyday situations, while their brain activation was continuously measured. We further measured the release of secretory immunoglobulin A (sIgA) in saliva to examine the first-line defensive response of the mucosal immune system. Perceiving sneezing and sick individuals compared to non-contagious individuals triggered increased activation in the anterior insula and other regions of the neuroimmune axis, that have been implicated in the somatosensory representation of the respiratory tract, and further led to increased release of sIgA. In line with predictions, this contagion cue-related activation of the insula was positively correlated with both perceived contagiousness and disgust evoked by the videos, as well as with the mucosal sIgA response. In contrast, the amygdala exhibited heightened activation to all videos featuring humans, regardless of explicit signs of contagion, indicating a nonspecific alertness to human presence. Nevertheless, amygdala activation was also correlated with the disgust ratings of each video. Collectively, these findings outline a neuroimmune mechanism for the processing of respiratory contagion cues. While the insula coordinates central and peripheral immune activation to match the perceived contagion threat, supposedly by triggering both increased sIgA release and contagion-related cognitions, the amygdala may rather act as an alerting system for social situations with a heightened transmission risk. This proactive neuroimmune response may help humans to manage contagion risks, that are difficult to avoid, by activating physiological and cognitive countermeasures in reaction to typical symptoms of respiratory infection, which prepares the organism for subsequent pathogen exposure.