Anticipatory synergy adjustments: preparing a quick action in an unknown direction

Zhou, Tao; Wu, Yen Hsun; Bartsch, Ángelo; Cuadra, Cristian; Zatsiorsky, Vladimir M.; Latash, Mark L.

doi:10.1007/s00221-013-3469-5

Cited by 25 publications

(16 citation statements)

References 34 publications

(46 reference statements)

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“…Other variables showed no clearly identifiable ASAs, possibly because the actions were not associated with fast enough changes in those variables. Note that the assumed function of ASA is to phase out synergies stabilizing a variable in preparation to its quick change (Zhou et al 2013); ASAs may not be needed if the variable does not change quickly.…”

Section: Discussionmentioning

confidence: 99%

Prehension synergies and hand function in early-stage Parkinson’s disease

Park

Lewis

et al. 2014

Exp Brain Res

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We explored the multi-digit synergies and hand performance in object manipulations and pressing tasks in patients with early-stage Parkinson’s disease (PD) and healthy controls. Synergies were defined as inter-trials co-variation patterns among forces/moments produced by individual digits that stabilized a resultant mechanical variable. The subjects performed three main tasks: Pressing (steady-state force production followed by a force pulse into the target), prehension (manipulation of a hand-held instrumented handle imitating the action of taking a sip from a glass), and functional object manipulation (moving a glass with water as quickly and accurately as possible along a chain of targets). The PD patients were slower compared to controls in all three tasks. Patients showed smaller synergy indices in the pressing and prehension tasks. In the prehension tasks, patients showed elevated grip force at steady states with smaller grip force modulation during the handle motion. PD patients showed smaller feed-forward synergy adjustments in preparation to the quick action in the pressing and (to a smaller degree) prehension tasks. Synergy indices correlated with the time index of performance in the functional glass-with-water task, whereas none of the indices correlated with the Unified PD Rating Scale part III – motor scores (UPDRS- III). We interpret the results as pointing at an important role of subcortical structures in motor synergies and their feed-forward adjustments to action.

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Section: Discussionmentioning

confidence: 99%

Prehension synergies and hand function in early-stage Parkinson’s disease

Park

Lewis

et al. 2014

Exp Brain Res

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“…Such synergic adjustments have been reported in force production tasks by a redundant set of effectors including bilateral tasks (19, 20). A recent study has shown that these adjustments are organized in a subtle way reflected in different patterns of force co-variation when the visual feedback was computed using varying gains for the force of one of the effectors (21). …”

Section: Discussionmentioning

confidence: 99%

Inter-limb force coupling is resistant to distorted visual feedback in chronic hemiparetic stroke

Li¹,

Durand-Sanchez²,

Latash³

2014

J Rehabil Med

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Objective Interlimb coupling between impaired and non-impaired limbs after stroke has been a common observation. The aim of this study was to examine interlimb interactions in force production in responses to altered visual gain in hemiparetic stroke survivors. Design prospective clinical study Methods A convenient sample of 7 hemiparetic stroke subjects (3 females and 4 males; mean 56.0 ± 12.8 years of age; history of stroke: mean 61.6 ± 53.3 months) participated in the study. Subjects performed bilateral elbow flexion to varying total force targets from 3% to 60% MVC with normal visual gain (1:1) and to a 10% MVC target with altered visual gains (1/8, ¼, ½, 2, 4, and 8) for the force of the less-impaired, ipsilesional side. Results Across all conditions, the forces produced by both impaired and non-impaired limb changed proportionally to their MVC force, such that relative contributions of each limb’s force to the total force remained unchanged. In conditions with altered visual gain, high and low, the total force showed errors in the direction of undershooting. Conclusion Our findings indicate that there is a strong interlimb force coupling in hemiparetic stroke, resistant to distorted visual feedback. It may reflect a default sharing pattern dominant after stroke.

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“…Depending on the context, high stability of biological movement may be beneficial (for example, during steady-state tasks) or detrimental (for example, during very fast actions). Recently, an ability of the central nervous system to adjust stability properties of an ongoing action has been discovered: Several studies have shown that humans have an ability to adjust their synergies in preparation for a quick action (Olafsdottir et al, 2005; Shim et al, 2005; Zhou et al, 2013). Such anticipatory synergy adjustments (ASAs) are seen as a drop in the synergy index (relative amount of V UCM in the total variance) 200–300 ms prior to the initiation of a quick action.…”

Section: The Application Of the Concept Of Motor Synergies To Quanmentioning

confidence: 99%

Neural control of movement stability: Lessons from studies of neurological patients

2015

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The concept of synergy provides a theoretical framework for movement stability resulting from the neural organization of multiple elements (digits, muscles, etc.) that all contribute to salient performance variables. Although stability of performance is obviously important for steady-state tasks leading to high synergy indices, a feed-forward drop in synergy indices is seen in preparation to a quick action (i.e., anticipatory synergy adjustments, ASAs). We review recent studies of multi-finger and multi-muscle synergies that show decreased indices of synergies and ASAs in patients with Parkinson’s disease (PD) or multisystem atrophy. In PD, the impairments in synergies and ASAs are partially reversed by dopaminergic drugs, and changes in synergy indices are present even in PD patients at earliest diagnosis. Taken together, these results point at subcortical structures that are crucial for proper control of movement stability. It is timely to introduce the concept of impaired control of stability as an objective, quantifiable, and theory-based clinical descriptor of movement disorders that can increase our understanding of the neural control of movement with all of its implications for clinical practice.

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Anticipatory synergy adjustments: preparing a quick action in an unknown direction

Cited by 25 publications

References 34 publications

Prehension synergies and hand function in early-stage Parkinson’s disease

Prehension synergies and hand function in early-stage Parkinson’s disease

Inter-limb force coupling is resistant to distorted visual feedback in chronic hemiparetic stroke

Neural control of movement stability: Lessons from studies of neurological patients

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