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Normalized Index of Synergy for Evaluating the Coordination of Motor Commands.

Togo S, Imamizu H - PLoS ONE (2015)

Bottom Line: We hypothesized that a large part of the change in the coordination of motor outputs through learning was because of changes in motor commands.In a motor learning task, subjects tracked a target trajectory of the total torque.We conclude that the normalized index of synergy can be used to evaluate the coordination of motor commands independently from the properties of the musculoskeletal system.

View Article: PubMed Central - PubMed

Affiliation: Cognitive Mechanisms Laboratories, Advanced Telecommunications Research Institute International, Kyoto, Japan; Japan Society for the Promotion of Science, Tokyo, Japan.

ABSTRACT
Humans perform various motor tasks by coordinating the redundant motor elements in their bodies. The coordination of motor outputs is produced by motor commands, as well properties of the musculoskeletal system. The aim of this study was to dissociate the coordination of motor commands from motor outputs. First, we conducted simulation experiments where the total elbow torque was generated by a model of a simple human right and left elbow with redundant muscles. The results demonstrated that muscle tension with signal-dependent noise formed a coordinated structure of trial-to-trial variability of muscle tension. Therefore, the removal of signal-dependent noise effects was required to evaluate the coordination of motor commands. We proposed a method to evaluate the coordination of motor commands, which removed signal-dependent noise from the measured variability of muscle tension. We used uncontrolled manifold analysis to calculate a normalized index of synergy. Simulation experiments confirmed that the proposed method could appropriately represent the coordinated structure of the variability of motor commands. We also conducted experiments in which subjects performed the same task as in the simulation experiments. The normalized index of synergy revealed that the subjects coordinated their motor commands to achieve the task. Finally, the normalized index of synergy was applied to a motor learning task to determine the utility of the proposed method. We hypothesized that a large part of the change in the coordination of motor outputs through learning was because of changes in motor commands. In a motor learning task, subjects tracked a target trajectory of the total torque. The change in the coordination of muscle tension through learning was dominated by that of motor commands, which supported the hypothesis. We conclude that the normalized index of synergy can be used to evaluate the coordination of motor commands independently from the properties of the musculoskeletal system.

No MeSH data available.


Related in: MedlinePlus

Human elbow model used in the simulation experiments.(a) The two elbow joint, eight muscle model. The four muscle tensions (T1–T4) generate the right elbow joint torque τr, and the others (T5–T8) generate the left elbow joint torque τl. The muscles T3, T4, T7, and T8 are the monoarticular muscles, and the others are the biarticular muscles. (b) The uncoordinated input corresponds to one point in the UCM. (c) The coordinated input corresponds to three points in the UCM.
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pone.0140836.g003: Human elbow model used in the simulation experiments.(a) The two elbow joint, eight muscle model. The four muscle tensions (T1–T4) generate the right elbow joint torque τr, and the others (T5–T8) generate the left elbow joint torque τl. The muscles T3, T4, T7, and T8 are the monoarticular muscles, and the others are the biarticular muscles. (b) The uncoordinated input corresponds to one point in the UCM. (c) The coordinated input corresponds to three points in the UCM.

Mentions: In this study, we considered a total elbow joint torque production task, wherein a subject produces isometric total elbow torque using both right and left elbows (Fig 3A). In this task, the performance variable is the sum of the right and left elbow torques, and the motor elements are the eight muscles associated with the flexion and extension of the right and left elbows. In the simulation experiments, we considered a model of a two-elbow joint with eight muscles, as shown in Fig 3A. In the target total torque production task measurement experiments, subjects produced total elbow joint torque toward a target total torque. In the learning task measurement experiments, subjects learned to track a target trajectory consisting of total elbow torque. Details of the experiments are described in the following sections.


Normalized Index of Synergy for Evaluating the Coordination of Motor Commands.

Togo S, Imamizu H - PLoS ONE (2015)

Human elbow model used in the simulation experiments.(a) The two elbow joint, eight muscle model. The four muscle tensions (T1–T4) generate the right elbow joint torque τr, and the others (T5–T8) generate the left elbow joint torque τl. The muscles T3, T4, T7, and T8 are the monoarticular muscles, and the others are the biarticular muscles. (b) The uncoordinated input corresponds to one point in the UCM. (c) The coordinated input corresponds to three points in the UCM.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4608756&req=5

pone.0140836.g003: Human elbow model used in the simulation experiments.(a) The two elbow joint, eight muscle model. The four muscle tensions (T1–T4) generate the right elbow joint torque τr, and the others (T5–T8) generate the left elbow joint torque τl. The muscles T3, T4, T7, and T8 are the monoarticular muscles, and the others are the biarticular muscles. (b) The uncoordinated input corresponds to one point in the UCM. (c) The coordinated input corresponds to three points in the UCM.
Mentions: In this study, we considered a total elbow joint torque production task, wherein a subject produces isometric total elbow torque using both right and left elbows (Fig 3A). In this task, the performance variable is the sum of the right and left elbow torques, and the motor elements are the eight muscles associated with the flexion and extension of the right and left elbows. In the simulation experiments, we considered a model of a two-elbow joint with eight muscles, as shown in Fig 3A. In the target total torque production task measurement experiments, subjects produced total elbow joint torque toward a target total torque. In the learning task measurement experiments, subjects learned to track a target trajectory consisting of total elbow torque. Details of the experiments are described in the following sections.

Bottom Line: We hypothesized that a large part of the change in the coordination of motor outputs through learning was because of changes in motor commands.In a motor learning task, subjects tracked a target trajectory of the total torque.We conclude that the normalized index of synergy can be used to evaluate the coordination of motor commands independently from the properties of the musculoskeletal system.

View Article: PubMed Central - PubMed

Affiliation: Cognitive Mechanisms Laboratories, Advanced Telecommunications Research Institute International, Kyoto, Japan; Japan Society for the Promotion of Science, Tokyo, Japan.

ABSTRACT
Humans perform various motor tasks by coordinating the redundant motor elements in their bodies. The coordination of motor outputs is produced by motor commands, as well properties of the musculoskeletal system. The aim of this study was to dissociate the coordination of motor commands from motor outputs. First, we conducted simulation experiments where the total elbow torque was generated by a model of a simple human right and left elbow with redundant muscles. The results demonstrated that muscle tension with signal-dependent noise formed a coordinated structure of trial-to-trial variability of muscle tension. Therefore, the removal of signal-dependent noise effects was required to evaluate the coordination of motor commands. We proposed a method to evaluate the coordination of motor commands, which removed signal-dependent noise from the measured variability of muscle tension. We used uncontrolled manifold analysis to calculate a normalized index of synergy. Simulation experiments confirmed that the proposed method could appropriately represent the coordinated structure of the variability of motor commands. We also conducted experiments in which subjects performed the same task as in the simulation experiments. The normalized index of synergy revealed that the subjects coordinated their motor commands to achieve the task. Finally, the normalized index of synergy was applied to a motor learning task to determine the utility of the proposed method. We hypothesized that a large part of the change in the coordination of motor outputs through learning was because of changes in motor commands. In a motor learning task, subjects tracked a target trajectory of the total torque. The change in the coordination of muscle tension through learning was dominated by that of motor commands, which supported the hypothesis. We conclude that the normalized index of synergy can be used to evaluate the coordination of motor commands independently from the properties of the musculoskeletal system.

No MeSH data available.


Related in: MedlinePlus