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Rapid prediction of biomechanical costs during action decisions

When given a choice between actions that yield the same reward, we tend to prefer the one that requires the least effort. Recent studies have shown that humans are remarkably accurate at evaluating the effort of potential reaching actions, and can predict the subtle energetic demand caused by the non-isotropic biomechanical properties of the arm. Here, we investigated the time course over which such information is computed and comes to influence decisions. Two independent approaches were used. First, subjects performed a reach decision task in which the time interval for deciding between two candidate reaching actions was varied from 200 to 800 ms. Second, we measured motor-evoked potential (MEPs) to single pulse transcranial magnetic stimulation (TMS) over the primary motor cortex (M1) to probe the evolving decision at different times after stimulus presentation. Both studies yielded a consistent conclusion: That a prediction of the effort associated with candidate movements is computed very quickly and influences decisions within 200 ms after presentation of the candidate actions. Furthermore, while the MEPs measured 150 ms after stimulus presentation were well correlated with the choices that subjects ultimately made, later in the trial the MEP amplitudes were primarily related to the muscular requirements of the chosen movement. This suggests that corticospinal excitability (CSE) initially reflects a competition between candidate actions, and later changes to reflect the processes of preparing to implement the winning action choice.

Ignasi Cos^1,3,4, Julie Duque², and Paul Cisek¹

¹Groupe de recherche sur le système nerveux central (GRSNC), Département de Neuroscience, Université de Montréal, Montréal (QC), CANADA

²Cognition and Action Laboratory, Institute of Neuroscience, Université Catholique de Louvain, 1200 Brussels, BELGIUM

³UPMC, Univ Paris 06, UMR 7222, ISIR, 4 Place Jussieu, 75005 Paris, FRANCE

⁴CRNS, UMR 7222, ISIR, 4 Place Jussieu, 75005 Paris, FRANCE