title: Characterization of reward and effort mechanisms in apathy.
abstract: Apathy is a common but poorly understood condition with a wide societal impact observed in several brain disorders as well as, to some extent, in the normal population. Hence the need for better characterization of the underlying mechanisms. The processes by which individuals decide to attribute physical effort to obtain rewards might be particularly relevant to relate to apathy traits. Here, we designed two paradigms to assess individual differences in physical effort production and effort-based decision-making and their relation to apathy in healthy people. Apathy scores were measured using a modified version of the Lille Apathy Rating Scale, suitable for use in a non-clinical population. In the first study, apathy scores were correlated with the degree to which stake (reward on offer) and difficulty level impacts on physical effort production. Individuals with relatively high apathy traits showed an increased modulation of effort while more motivated individuals generally exerted greater force across different levels of stake. To clarify the underlying mechanisms for this behavior, we designed a second task that allows independent titration of stake and effort levels for which subjects are willing to engage in an effortful response to obtain a reward. Our results suggest that apathy traits in the normal population are related to the way reward subjectively affects the estimation of effort costs, and more particularly manifest as decreased willingness to exert effort when rewards are small, or below threshold. The tasks we introduce here may provide useful tools to further investigate apathy in clinical populations.
authors.affiliation: Dept. of Experimental Psychology, University of Oxford, Oxford, UK. Electronic address: valerie.bonnelle@psy.ox.ac.uk.
authors.forename: Valerie
authors.initials: V
authors.lastname: Bonnelle
authors.affiliation: Dept. of Experimental Psychology, University of Oxford, Oxford, UK.
authors.forename: Kai-Riin
authors.initials: KR
authors.lastname: Veromann
authors.affiliation: Dept. of Experimental Psychology, University of Oxford, Oxford, UK.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Burnett Heyes
authors.affiliation: Dept. of Experimental Psychology, University of Oxford, Oxford, UK.
authors.forename: Elena
authors.initials: E
authors.lastname: Lo Sterzo
authors.affiliation: Dept. of Experimental Psychology, University of Oxford, Oxford, UK; Institute of Cognitive Neuroscience, University College London, UK.
authors.forename: Sanjay
authors.initials: S
authors.lastname: Manohar
authors.affiliation: Dept. of Experimental Psychology, University of Oxford, Oxford, UK; Nuffield Dept. Clinical Neurosciences, University of Oxford, Oxford, UK.
authors.forename: Masud
authors.initials: M
authors.lastname: Husain
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000465:Algorithms; D000704:Analysis of Variance; D057565:Apathy; D003657:Decision Making / Q000502:physiology*; D030141:Feedback, Psychological; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009042:Motivation / Q000502:physiology*; D012201:Reward; D013223:Statistics as Topic; D055815:Young Adult
keywords: Action Initiation; Apathy; Decision-making; Effort discounting; Motivation
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