Neural mechanisms underlying the effects of physical fatigue on effort-based choice

Abstract

Physical fatigue crucially influences our decisions to partake in effortful action. However, there is a limited understanding of how fatigue impacts effort-based decision-making at the level of brain and behavior. We use functional magnetic resonance imaging to record markers of brain activity while human participants engage in uncertain choices for prospective physical effort, before and after bouts of exertion. Using computational modeling of choice behavior we find that fatiguing exertions cause participants to increase their subjective cost of effort, compared to a baseline/rested state. We describe a mechanism by which signals related to motor cortical state in premotor cortex influence effort value computations, instantiated by insula, thereby increasing an individual's subjective valuation of prospective physical effort while fatigued. Our findings provide a neurobiological account of how information about bodily state modulates decisions to engage in physical activity.

Chronic Restraint Stress-Induced Muscle Atrophy Leads to Fatigue in Mice by Inhibiting the AMPK Signaling Pathway

“…Stress and physical activity are believed to be interrelated; stress may cause muscle fatigue and reduced muscle contraction ability, while physical exercise can counter stress [22]. However, in clinical observation, fatigue may reduce people's willingness to exercise actively in a quiet state [23]. This was also observed in our OFT results; locomotor activity significantly decreased after treatment with CRS for 15 days.…”

Heightened effort discounting is a common feature of both apathy and fatigue

“…the more transient state that arises during the exertion of effort itself 15 ), and early commentaries suggested that lower motivation is a central mechanism that drives the experience of fatigue 2 . This idea has received renewed interest in recent times, as a result of data that have implicated neural systems classically involved in value-based decision-making in both traits 7 , 8 , 16 – 18 .…”

“…Effort discounting tasks have become a popular paradigm to quantify the motivation of individuals to engage in goal-directed activity 16 , 19 – 22 . Such tasks quantify the effect of effort on reducing (or ‘discounting’) the subjective value of available rewards, which is computationally measured as the gradient of each individual’s effort discounting function 1 , 23 – 25 .…”

“…Historically, effort discounting has predominantly been used to study the neurobiology of apathy 1 , 25 – 29 . More recently, however, a nascent literature has begun to apply effort discounting paradigms to quantify fatigue 16 , 21 , 30 – 32 . Given the frequent co-existence of apathy and fatigue, this raises immediate concerns about interpreting effort discounting data in terms of each trait to the exclusion of the other.…”

Fatigue in Cirrhosis

“…could be critical for generating feelings of effort and fatigue. 3 The concept that fatigue could be a disease entity in itself and not just a symptom of pathological /clinical conditions gained traction after acceptance of ME/CFS [meningo-encephalomyelitis/chronic fatigue syndrome] as a chronic complex systemic disease. ME/CFS has distinct diagnostic criteria, [Institute of Medicine criteria, iom.nationalacademies.org/reports/2015/me-cfs aspx]., case definition and biological abnormalities These are: post exertional malaise, unrefreshing sleep, cognitive impairment and orthostatic intolerance.…”