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Optimal control of bias as a principle for the control of posture and movement| old_uid | 7412 |
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| title | Optimal control of bias as a principle for the control of posture and movement |
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| start_date | 2009/10/08 |
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| schedule | 11h30 |
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| online | no |
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| summary | Motor behavior is a natural and continuous superimposition of movement periods, generally involving large and rapid displacements of focal body segments to subserve goal-directed actions, and posture periods, made of small and slow displacements of the whole body to achieve postural orientation and equilibrium maintenance (Massion 1992). The nature of the coordination process between posture and movement is unknown, and remains a central and highly debated issue in the field of motor control (Ostry & Feldman 2003; Kurtzer et al. 2005).
The controversy is centered on two possible computational schemes. On the one hand, it has been proposed that movement results from continuous transitions between postures (Ostry & Feldman 2003). On the other hand, coordination could emerge from the combination of separate processes (Kawato 1999), one that translates desired kinematics into appropriate forces (inverse dynamics), and another that creates feedback corrections based on deviations from the desired kinematics (impedance control). The two schemes have different qualities, but the same drawbacks. First, as they elaborate control signals based on a desired trajectory, they fail to account for the flexibility of motor behavior (Todorov & Jordan 2002). Second, they consider posture maintenance as a passive, impedance-based process which is likely to be scarcely robust and stable in the face of transmission delays and low levels of actuator stiffness (Morasso & Schieppati 1999; Loram & Lakie 2002).
A third line of thinking has recently emerged from the observation that posture likely results from a high-level, active, anticipatory process rather than from a low-level, passive, feedback process (Morasso & Schieppati 1999; Loram et al. 2001). According to this view, postural control would not be different from movement control. If this is the case, it remains to be proven that principles that are efficient to account for movement control (optimal feedback control; Todorov & Jordan 2002) can also be applied to postural control. Here we show that optimal feedback control applied to the bias of a spring in a compliant linkage explains the intermittent nature of human postural sway and inverted pendulum movements (Lakie et al. 2003), and the paradoxical nature of muscle movements in standing (Loram et al. 2004). On this basis, we propose that one and the same process is involved in the control of posture and movement.
References
Kawato M (1999) Curr Opin Neurobiol 9:718 ? - Kurtzer I, Herter TM, Scott SH (2005) Nat Neurosci 8:498 - Loram ID, Kelly SM, Lakie M (2001) J Physiol (Lond) 532:879 - Loram ID, Lakie M (2002) J Physiol (Lond) 540:1111 - Lakie M, Caplan N, Loram ID (2003) J Physiol (Lond) 551:357 - Loram ID, Maganaris CN, Lakie M (2004) J Physiol (Lond) 556:683 - Massion J (1992) Prog Neurobiol 38:35 - Morasso PG, Schieppati M (1999) J Neurophysiol 82:1622 - Ostry DJ, Feldman AG (2003) Exp Brain Res 153:275 - Todorov E, Jordan MI (2002) Nat Neurosci 5:1226. |
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| responsibles | Béranger |
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