'Bodily precision': a predictive coding account of individual differences in interoceptive accuracy

Abstract

Individuals differ in their awareness of afferent information from within their bodies, which is typically assessed by a heartbeat perception measure of 'interoceptive accuracy' (IAcc). Neural and behavioural correlates of this trait have been investigated, but a theoretical explanation has yet to be presented. Building on recent models that describe interoception within the free energy/predictive coding framework, this paper applies similar principles to IAcc, proposing that individual differences in IAcc depend on 'precision' in interoceptive systems, i.e. the relative weight accorded to 'prior' representations and 'prediction errors' (that part of incoming interoceptive sensation not accounted for by priors), at various levels within the cortical hierarchy and between modalities. Attention has the effect of optimizing precision both within and between sensory modalities. Our central assumption is that people with high IAcc are able, with attention, to prioritize interoception over other sensory modalities and can thus adjust the relative precision of their interoceptive priors and prediction errors, where appropriate, given their personal history. This characterization explains key findings within the interoception literature; links results previously seen as unrelated or contradictory; and may have important implications for understanding cognitive, behavioural and psychopathological consequences of both high and low interoceptive awareness.This article is part of the themed issue 'Interoception beyond homeostasis: affect, cognition and mental health'.

Keywords: free energy; heartbeat perception; interoception; interoceptive accuracy; predictive coding.

Figure 1.

Schematic overview of the hierarchical message passing in the brain that is assumed to underlie predictive coding. Predictions (priors) are illustrated as black lines that project down the levels of the hierarchy, from prediction units (deep pyramidal cells) shown as black triangles. Forward projecting prediction errors are represented by red lines, passing up the hierarchy from prediction error units (superficial pyramidal cells), which are represented by red triangles. Importantly, PEs and predictions occur at every level. The dashed red and black arrows indicate local processing within a level. At level 1, they thus represent an autonomic reflex. Precision, which plays the crucial role of determining the relative weight of the PEs versus the priors, at every level of the hierarchy, passes down the hierarchy and is indicated by the blue arrows. A percept is formed when PE is minimized at all levels within the hierarchy. Adapted from Edwards et al. [6].

Figure 2.

The graphs show Gaussian probability distributions representing, at one particular level in the hierarchy, the descending prior and posterior and the ascending PEs (which arises from the incoming sensory data). These distributions refer to some hidden state of the organism (e.g. some aspect of its interoceptive state) that has to be inferred. The widths of the various distributions correspond to their variance. Precision is the inverse of variance. The relative precision of PEs and prior is crucial in determining the updating of the prior to the posterior. (a) A context in which the precision of the PEs is precise (relative to the prior), so that the posterior is shifted towards the PEs (arrow). (b) By contrast, imprecise PEs have little impact on the prior. The posterior then descends to the level below this in the hierarchy where it becomes, in turn, the empirical prior. Adapted from Adams et al. [23].