Abstract
Fatigue is a common experience in both health and disease. Yet, pathological (i.e., prolonged or chronic) and transient (i.e., exertional) fatigue symptoms are traditionally considered distinct, compounding a separation between interested research fields within the study of fatigue. Within the clinical neurosciences, nascent frameworks position pathological fatigue as a product of inference derived through hierarchical predictive processing. The metacognitive theory of dyshomeostasis (Stephan et al., 2016) states that pathological fatigue emerges from the metacognitive mechanism in which the detection of persistent mismatches between prior interoceptive predictions and ascending sensory evidence (i.e., prediction error) signals low evidence for internal generative models, which undermine an agent’s feeling of mastery over the body and is thus experienced phenomenologically as fatigue. Although acute, transient subjective symptoms of exertional fatigue have also been associated with increasing interoceptive prediction error, the dynamic computations that underlie its development have not been clearly defined. Here, drawing on the metacognitive theory of dyshomeostasis, we extend this account to offer an explicit description of the development of fatigue during extended periods of (physical) exertion. Accordingly, it is proposed that a loss of certainty or confidence in control predictions in response to persistent detection of prediction error features as a common foundation for the conscious experience of both pathological and nonpathological fatigue.
Highlights
The experience of fatigue is ubiquitous in both health and disease
We describe a neurocomputational account of the subjective perception of fatigue that emerges in response to changing perceptions of control efficacy during demanding physical exertion, based on a predictive processing framework
We propose that the suppression of prediction error at all lower-levels during the maintenance of goal-directed action driven by higher levels, is subject to the same metacognitive appraisal as described in the conceptualisation of pathological fatigue
Summary
The experience of fatigue is ubiquitous in both health and disease. the concept of fatigue is firmly embedded within modern life, typical lay understanding of what is meant. Stephan et al.'s (2016) compelling model provides a computational account of pathological fatigue, which the authors contend may be formally distinguished from the acute, transient exertional fatigue experienced in health (referred to by the authors as “tiredness”3) In this model, changes at a somatic level and/or within the hierarchical system’s circuitry in response to disease disrupts computational functions (which may involve various levels of the hierarchy) such that dyshomeostasis (error within the interoceptive model) is persistently experienced, engendering a perceived lack of control over bodily states which in turn fosters the conscious perception of fatigue. Effort perception during motor tasks has been associated with trait fatigue in clinical populations, such as stroke survivors, suffering from chronic fatigue (De Doncker et al, 2020)6 This may be explained within the proposed model as follows: lower precision estimates in prior beliefs at higher levels emerging with (exertional) fatigue (reflecting increasing uncertainty in model predictions) cause greater prediction error at lower levels. Whether changes in effective connectivity between key nodes is associated with the development of exertional fatigue has yet to be elucidated
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