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Halla B. Olafsdottir, Sun Wook Kim, Vladimir M. Zatsiorsky and Mark L. Latash

We tested the ability of healthy elderly persons to use anticipatory synergy adjustments (ASAs) prior to a self-triggered perturbation of one of the fingers during a multifinger force production task. An index of a force-stabilizing synergy was computed reflecting covariation of commands to fingers. The subjects produced constant force by pressing with the four fingers of the dominant hand on force sensors against constant upwardly directed forces. The middle finger could be unloaded either by the subject pressing the trigger or unexpectedly by the experimenter. In the former condition, the synergy index showed a drop (interpreted as ASA) prior to the time of unloading. This drop started later and was smaller in magnitude as compared with ASAs reported in an earlier study of younger subjects. At the new steady state, a new sharing pattern of the force was reached. We conclude that aging is associated with a preserved ability to explore the flexibility of the mechanically redundant multifinger system but a decreased ability to use feed-forward adjustments to self-triggered perturbations. These changes may contribute to the documented drop in manual dexterity with age.

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Mitchell Tillman and Satyajit Ambike

-offs have been observed in locomotor ( Acasio, Wu, Fey, & Gordon, 2017 ) and upright postural tasks ( Huang & Ahmed, 2011 ). Furthermore, the phenomenon of anticipatory synergy adjustment (ASA), describing the influence of upcoming voluntary movements on the stability of the current motor pattern, has been

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Mark L. Latash

potential well (point a ). To move this system to another coordinate (point b ), one can start with destabilizing it (anticipatory synergy adjustment [ASA]) without changing its state. (B) ASAs are observed prior to quick force pulse production as a drop in the synergy index, ΔV, 200–300 ms prior to the

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Mark L. Latash

The target article presents a review of the neural control of the human hand. The review emphasizes the physical approach to motor control. It focuses on such concepts as equilibrium-point control, control with referent body configurations, uncontrolled manifold hypothesis, principle of abundance, hierarchical control, multidigit synergies, and anticipatory synergy adjustments. Changes in aspects of the hand neural control with age and neurological disorder are discussed. The target article is followed by six commentaries written by Alexander Aruin, Kelly Cole, Monica Perez, Robert Sainburg, Marco Sanello, and Wei Zhang.

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Mark L. Latash

Living systems may be defined as systems able to organize new, biology-specific, laws of physics and modify their parameters for specific tasks. Examples include the force-length muscle dependence mediated by the stretch reflex, and the control of movements with modification of the spatial referent coordinates for salient performance variables. Low-dimensional sets of referent coordinates at a task level are transformed to higher-dimensional sets at lower hierarchical levels in a way that ensures stability of performance. Stability of actions can be controlled independently of the actions (e.g., anticipatory synergy adjustments). Unintentional actions reflect relaxation processes leading to drifts of corresponding referent coordinates in the absence of changes in external load. Implications of this general framework for movement disorders, motor development, motor skill acquisition, and even philosophy are discussed.

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Mark L. Latash

The article offers a way to unite three recent developments in the field of motor control and coordination: (1) The notion of synergies is introduced based on the principle of motor abundance; (2) The uncontrolled manifold hypothesis is described as offering a computational framework to identify and quantify synergies; and (3) The equilibrium-point hypothesis is described for a single muscle, single joint, and multijoint systems. Merging these concepts into a single coherent scheme requires focusing on control variables rather than performance variables. The principle of minimal final action is formulated as the guiding principle within the referent configuration hypothesis. Motor actions are associated with setting two types of variables by a controller, those that ultimately define average performance patterns and those that define associated synergies. Predictions of the suggested scheme are reviewed, such as the phenomenon of anticipatory synergy adjustments, quick actions without changes in synergies, atypical synergies, and changes in synergies with practice. A few models are briefly reviewed.

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. McGill * 5 2008 24 2 166 174 10.1123/jab.24.2.166 Anticipatory Synergy Adjustments in Preparation to Self-Triggered Perturbations in Elderly Individuals Halla B. Olafsdottir * Sun Wook Kim * Vladimir M. Zatsiorsky * Mark L. Latash * 5 2008 24 2 175 179 10.1123/jab.24.2.175 Technical Notes

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Julie Vaughan-Graham, Kara Patterson, Karl Zabjek and Cheryl A. Cott

( Krishnan, Aruin, & Latash, 2011 ; Massion, Alexandrov, & Frolov, 2004 ; Santos, Kanekar, & Aruin, 2010a , 2010b ). In addition to early postural adjustments and anticipatory postural adjustments, there is a developing body of literature on anticipatory synergy adjustments. Anticipatory synergy

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Christopher A. DiCesare, Scott Bonnette, Gregory D. Myer and Adam W. Kiefer

( 5 ), 504 – 508 . doi:10.1016/j.clinbiomech.2011.01.004 10.1016/j.clinbiomech.2011.01.004 Klous , M. , Mikulic , P. , & Latash , M.L. ( 2011 ). Two aspects of feedforward postural control: Anticipatory postural adjustments and anticipatory synergy adjustments . Journal of Neurophysiology

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Momoko Yamagata, Ali Falaki and Mark L. Latash

.gaitpost.2016.01.006 Klous , M. , Mikulic , P. , & Latash , M.L. ( 2011 ). Two aspects of feed-forward postural control: Anticipatory postural adjustments and anticipatory synergy adjustments . Journal of Neurophysiology, 105 , 2275 – 2288 . PubMed ID: 21389305 doi:10.1152/jn.00665.2010 10.1152/jn