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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

Change in the tracking performance through motor learning.(a) The duration of out of margin tout. (b) The feedback gain G (Eq (11)). The blue, green and red bars indicate the pre-test, the learning phases, and the post-test, respectively. The asterisk indicates a significant difference (P < 0.05). Specific values are listed in S3 Table.
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pone.0140836.g008: Change in the tracking performance through motor learning.(a) The duration of out of margin tout. (b) The feedback gain G (Eq (11)). The blue, green and red bars indicate the pre-test, the learning phases, and the post-test, respectively. The asterisk indicates a significant difference (P < 0.05). Specific values are listed in S3 Table.

Mentions: To demonstrate the usability of our proposed method, we conducted a tracking-ability learning task. Fig 8 shows the tracking performance, the duration of time outside the margin tout (Fig 8A) and the feedback gain G (in Eq (11) and Fig 8B), for all subjects. The duration outside the margin tout gradually decreased through learning, and was significantly smaller in post-test than in pre-test (F(7, 72) = 4.1, P = 7.74 × 10−4 < 0.05). This result indicates that subjects could significantly learn to accurately track the target trajectory of total elbow torque. The feedback gain G gradually increased through learning, and was significantly larger in L6 (sixth learning phase) than in L1 (F(7, 72) = 10.0, P = 1.10 × 10−8 < 0.05). This result indicates that subjects could gradually learn a more difficult task in later learning phases.


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

Togo S, Imamizu H - PLoS ONE (2015)

Change in the tracking performance through motor learning.(a) The duration of out of margin tout. (b) The feedback gain G (Eq (11)). The blue, green and red bars indicate the pre-test, the learning phases, and the post-test, respectively. The asterisk indicates a significant difference (P < 0.05). Specific values are listed in S3 Table.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4608756&req=5

pone.0140836.g008: Change in the tracking performance through motor learning.(a) The duration of out of margin tout. (b) The feedback gain G (Eq (11)). The blue, green and red bars indicate the pre-test, the learning phases, and the post-test, respectively. The asterisk indicates a significant difference (P < 0.05). Specific values are listed in S3 Table.
Mentions: To demonstrate the usability of our proposed method, we conducted a tracking-ability learning task. Fig 8 shows the tracking performance, the duration of time outside the margin tout (Fig 8A) and the feedback gain G (in Eq (11) and Fig 8B), for all subjects. The duration outside the margin tout gradually decreased through learning, and was significantly smaller in post-test than in pre-test (F(7, 72) = 4.1, P = 7.74 × 10−4 < 0.05). This result indicates that subjects could significantly learn to accurately track the target trajectory of total elbow torque. The feedback gain G gradually increased through learning, and was significantly larger in L6 (sixth learning phase) than in L1 (F(7, 72) = 10.0, P = 1.10 × 10−8 < 0.05). This result indicates that subjects could gradually learn a more difficult task in later learning phases.

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