10 11 A growing body of evidence highlights the intricate linkage of exteroceptive perception to 12 the rhythmic activity of the visceral body. In parallel, interoceptive inference theories of 13 emotion and self-consciousness are on the rise in cognitive science. However, thus far no 14 formal theory has emerged to integrate these twin domains; instead most extant work is 15 conceptual in nature. Here, we introduce a formal model of cardiac active inference, which 16 explains how ascending cardiac signals entrain exteroceptive sensory perception and 17 confidence. Through simulated psychophysics, we reproduce the defensive startle reflex and 18 commonly reported effects linking the cardiac cycle to fear perception. We further show that 19 simulated 'interoceptive lesions' blunt fear expectations, induce psychosomatic 20 hallucinations, and exacerbate metacognitive biases. Through synthetic heart-rate 21 variability analyses, we illustrate how the balance of arousal-priors and visceral prediction 22 errors produces idiosyncratic patterns of physiological reactivity. Our model thus offers the 23 possibility to computationally phenotype disordered brain-body interaction. 24 25 26 Our focus on the multimodal integration of interoceptive and exteroceptive domains 60 is driven by the overwhelming evidence for interoception as a key modality in hedonics, 61 arousal, emotion and selfhood Apps and Tsakiris, 2014; Gallagher 62 and Allen, 2018;Seth, 2013;Seth and Friston, 2016). This is generally treated under the 63 rubric of interoceptive inference; namely, active inference in the interoceptive domain. 64There are several compelling formulations of interoceptive inference from the perspective 65 of neurophysiology, neuroanatomy and, indeed, issues of consciousness in terms of minimal 66 selfhood. However, much of this treatment rests upon a purely conceptual analysis -67 underpinned by some notion of active (Bayesian) inference about states of the world 68 (including the body). In this work, we offer a more formal (mathematical) analysis that we 69 hope will be a point of reference for both theoretical and empirical investigations. 70In brief, we constructed a (minimal) active inference architecture to simulate 71 embodied perception and concomitant arousal. Here, we focused on simulating interactions 72 between the cardiac cycle and exteroceptive perception. In principle however, our 73 simulation provides a computational proof-of-principle that can be expanded to understand 74 brain-body coupling at any physiological or behavioral timescale. Using a Markov decision 75 process formulation, we created a synthetic subject who exhibited physiological (cardio-76 acceleration) responses to arousing stimuli. Our agenda was twofold: first, to provide a 77 sufficiency proof that -in at least one example -the interaction between interoception and 78 exteroception emerges from the normative (formal) principles of active inference. 79 Furthermore, having an in silico subject at hand, means that we can simulate the effects of...
