How Stress Can Change Our Deepest Preferences: Stress Habituation Explained Using the Free Energy Principle

Abstract

People who habituate to stress show a repetition-induced response attenuation—neuroendocrine, cardiovascular, neuroenergetic, and emotional—when exposed to a threatening environment. But the exact dynamics underlying stress habituation remain obscure. The free energy principle offers a unifying account of self-organising systems such as the human brain. In this paper, we elaborate on how stress habituation can be explained and modelled using the free energy principle. We introduce habituation priors that encode the agent’s tendency for stress habituation and incorporate them in the agent’s decision-making process. Using differently shaped goal priors—that encode the agent’s goal preferences—we illustrate, in two examples, the optimising (and thus habituating) behaviour of agents. We show that habituation minimises free energy by reducing the precision (inverse variance) of goal preferences. Reducing the precision of goal priors means that the agent accepts adverse (previously unconscionable) states (e.g., lower social status and poverty). Acceptance or tolerance of adverse outcomes may explain why habituation causes people to exhibit an attenuation of the stress response. Given that stress habituation occurs in brain regions where goal priors are encoded, i.e., in the ventromedial prefrontal cortex and that these priors are encoded as sufficient statistics of probability distributions, our approach seems plausible from an anatomical-functional and neuro-statistical point of view. The ensuing formal and generalisable account—based on the free energy principle—further motivate our novel treatment of stress habituation. Our analysis suggests that stress habituation has far-reaching consequences, protecting against the harmful effects of toxic stress, but on the other hand making the acceptability of precarious living conditions and the development of the obese type 2 diabetes mellitus phenotype more likely.

Obesity and Type 2 Diabetes Mellitus Explained by the Free Energy Principle

“…If our goal beliefs cannot be met, then as a last resort, the goal itself may be changed. It has been shown that changing goal priors can indeed reduce uncertainty (Hartwig et al, 2022). However, changing goal priors comes at a significant cost, as we have to sacrifice our deepest preferences.…”

“…Those people who are uncertain in answering this question experience stress. Uncertainty is used here as 'entropy' in terms of information theory (Shannon, 1948) and means, in the context of stress, that even when people choose their most promising policy, they expect surprises, i.e., they remain uncertain about what will happen next (Hartwig et al, 2022).…”

“…So far, the free energy principle has been successfully applied to explain various brain processes such as perception, action, attention, learning, decision making, exploration, and social cooperation (Hohwy, 2013;Schwartenbeck et al, 2013;Clark, 2016;Hartwig and Peters, 2021). Here we apply the free energy principle to stress, it being a state where all available policies of the agent display a heightened expected free energy (Hartwig et al, 2022).…”

“…Tolerable stress occurs in people who habituated to stress. Toxic stress occurs in people for whom stress habituation was not a free-energy-optimal solution and who therefore did not habituate (Hartwig et al, 2022). Compared to people who experience good stress, people with tolerable or toxic stress can develop prolonged changes in cerebral energy metabolism.…”

“…After stress habituation, people typically tend to develop the corpulent-but-waisted phenotype and, under toxic stress, the lean-but-narrow-waisted phenotype, the latter being associated with a high risk of cardio-and cerebrovascular complications. Both phenotypes have a high risk for type 2 diabetes mellitus (Peters and McEwen, 2015;Peters et al, 2017;Hartwig et al, 2022).…”