Julie Lasselin

The question of how emotions are triggered remains obscure. A recent influential theory is built on predicting coding, which states that the brain makes predictions and constantly compares these predictions with the actual incoming sensory information. The active inference theory of emotions posits that emotions arise when there is a mismatch between the bodily (interoceptive) sensations and what was predicted by the brain, i.e. when interoceptive prediction errors occur. This theory is extremely relevant for emotional disorders linked with infections (e.g. post-COVID), since infections can trigger various and intense interoceptive signals that can be difficult to predict by the brain. In this project, we will apply the active inference theory of emotions in an ecologically relevant model of infection, using an innovative experimental approach. We will go beyond the existing correlational designs by applying a causal intervention eliciting real sickness symptoms, and manipulating interoceptive prediction errors directly, in 240 participants. We hypothesize that emotional responses will arise during sickness when interoceptive prediction errors occur, i.e. when interoceptive sensations violate predictions. This project will therefore provide critical information to understand how individuals' predictions shape sickness behavior, and how emotions are generated in infection-related conditions, which could open new therapies for mood disorders associated with immune activation.

Infectious diseases have always been and still are a major cause of human death, causing fatal epidemics worldwide. This project aims to resolve the paradox that while the most effective defense strategy would be to avoid every sick individual, humans do not

instead, some sick individuals are approached for caregiving purposes. In fact, most care needs are met by family members, suggesting that kin selection strongly affects human responses to sickness cues. This interdisciplinary project will be the first to address whether early facial cues of sickness influence humans’ decisions to avoid or approach (i.e. care for) sick individuals and to what degree kinship moderates such decisions. In study 1, we will establish whether facial photographs of sick individuals induce spatial and social avoidance by using novel methods from experimental psychology and economics. In study 2, we will use cutting-edge digital morphing techniques to experimentally increase facial resemblance, and establish whether this cue of kinship suppresses avoidance of sick kin or even induces an approach behavior. In study 3, we will investigate whether the mere sight of early sickness cues activates the immune system, a mechanism that may enable approach, especially caregiving, by preparing the human body for an infectious attack. This project will answer fundamental questions of human behavioral immunity, a field that will benefit a world whose inhabitants are increasingly at risk from pandemics.