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Does the brain use intermittent or continuous control ?| old_uid | 3746 |
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| title | Does the brain use intermittent or continuous control ? |
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| start_date | 2007/12/20 |
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| schedule | 11h30 |
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| online | no |
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| details | Pierre Baraduc, CNRS UMR 5229, invite toute personne intéressée à la conférence |
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| summary | “Nature sets in motion by signs and watchwords, which are made with little momentum…Just as in the army the soldiers are set in motion by one word as if by a given signal and continue to move until they receive another signal to stop, so the muscles move in order and harmony from established custom.” William Harvey (1578-1657)
Following the cybernetics tradition we consider successful engineering tools as models for the biological system. In this study we consider the bang-bang control method. We assume that the central nervous system issues piecewise constant signals as motor commands (i.e., piecewise constant firing rates) and determine the timing and amplitude of each burst. We hypothesize that the musculoskeletal dynamics shape and smooth the control signal and that the synergies evolved to minimize the effort of the central nervous system as measured by the number of transitions between constant neural activities - namely the minimum transition hypothesis.
We consider the well studied point to point reaching movement and the numerous possible optimization criteria that were proposed in order to account for the observed bell shaped speed profile. Among the end-point related criteria, the possible minimum acceleration criterion was rejected due to the predicted jump in acceleration at the initiation of the movement and the minimum Jerk was found to best fit the experimental observations. We considered a constraint version of the minimum acceleration model in which the jerk is limited. We show that the minimum acceleration with constraints criterion predicts bell shaped speed profile in which the control signal includes two transitions, i.e., three phase control signal which is both physiologically plausible and consistent with our intermittence control hypothesis above.
I’ll start the talk with a short survey of my recent and current research projects related to perception of delayed stiffness, motor memory and a case study about lack of predictive control in children with Cerebral Palsy, and then I'll concentrate on the main topic described above and conclude with a brief description of the recently funded collaboration with Dr. Pierre Baraduc. |
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| responsibles | Béranger |
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