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Do muscle synergies reduce the dimensionality of behavior?

Kuppuswamy N, Harris CM - Front Comput Neurosci (2014)

Bottom Line: Dimensionality of various reaching trajectories is compared when using idealized temporal synergies.The results indicate that a trajectory and synergy basis specific DR of behavior results from muscle synergy control.The implications of these results for the synergy hypothesis, optimal motor control, motor development, and robotics are discussed.

View Article: PubMed Central - PubMed

Affiliation: Artificial Intelligence Laboratory, Department of Informatics, University of Zürich Zürich, Switzerland.

ABSTRACT
The muscle synergy hypothesis is an archetype of the notion of Dimensionality Reduction (DR) occurring in the central nervous system due to modular organization. Toward validating this hypothesis, it is important to understand if muscle synergies can reduce the state-space dimensionality while maintaining task control. In this paper we present a scheme for investigating this reduction utilizing the temporal muscle synergy formulation. Our approach is based on the observation that constraining the control input to a weighted combination of temporal muscle synergies also constrains the dynamic behavior of a system in a trajectory-specific manner. We compute this constrained reformulation of system dynamics and then use the method of system balancing for quantifying the DR; we term this approach as Trajectory Specific Dimensionality Analysis (TSDA). We then investigate the consequence of minimization of the dimensionality for a given task. These methods are tested in simulations on a linear (tethered mass) and a non-linear (compliant kinematic chain) system. Dimensionality of various reaching trajectories is compared when using idealized temporal synergies. We show that as a consequence of this Minimum Dimensional Control (MDC) model, smooth straight-line Cartesian trajectories with bell-shaped velocity profiles emerged as the optima for the reaching task. We also investigated the effect on dimensionality due to adding via-points to a trajectory. The results indicate that a trajectory and synergy basis specific DR of behavior results from muscle synergy control. The implications of these results for the synergy hypothesis, optimal motor control, motor development, and robotics are discussed.

No MeSH data available.


Dimensionality analysis for via-point tasks. (A) A set of cartesian via-points were specified on a circle of radius 0.216 m centered on the target (0.4, 0.2) for a reaching movement from the initial position; (B) Polar plot of the variation in the dimensionality performance index against orientation of via-point with respect to origin. The minimum index of 11.21 is located at the orientation of 286.15° corresponding to the via-point at (0.61, 0.14) which is very close to the straight line linking origin and target.
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Figure 10: Dimensionality analysis for via-point tasks. (A) A set of cartesian via-points were specified on a circle of radius 0.216 m centered on the target (0.4, 0.2) for a reaching movement from the initial position; (B) Polar plot of the variation in the dimensionality performance index against orientation of via-point with respect to origin. The minimum index of 11.21 is located at the orientation of 286.15° corresponding to the via-point at (0.61, 0.14) which is very close to the straight line linking origin and target.

Mentions: As in the earlier linear system experiments, we use the MDC framework to analyze the reduction in dimensionality in via-point tasks. Via-points are chosen to lie on a circle about the target position (as seen in Figure 10). Again, the via-points are specified to be reached at exactly at half of the movement duration. For each trajectory, the appropriate synergy weight matrix was computed. The variation of the dimensionality performance index with respect to via-point orientation is obtained, as seen in the polar plot in Figure 10B.


Do muscle synergies reduce the dimensionality of behavior?

Kuppuswamy N, Harris CM - Front Comput Neurosci (2014)

Dimensionality analysis for via-point tasks. (A) A set of cartesian via-points were specified on a circle of radius 0.216 m centered on the target (0.4, 0.2) for a reaching movement from the initial position; (B) Polar plot of the variation in the dimensionality performance index against orientation of via-point with respect to origin. The minimum index of 11.21 is located at the orientation of 286.15° corresponding to the via-point at (0.61, 0.14) which is very close to the straight line linking origin and target.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4066703&req=5

Figure 10: Dimensionality analysis for via-point tasks. (A) A set of cartesian via-points were specified on a circle of radius 0.216 m centered on the target (0.4, 0.2) for a reaching movement from the initial position; (B) Polar plot of the variation in the dimensionality performance index against orientation of via-point with respect to origin. The minimum index of 11.21 is located at the orientation of 286.15° corresponding to the via-point at (0.61, 0.14) which is very close to the straight line linking origin and target.
Mentions: As in the earlier linear system experiments, we use the MDC framework to analyze the reduction in dimensionality in via-point tasks. Via-points are chosen to lie on a circle about the target position (as seen in Figure 10). Again, the via-points are specified to be reached at exactly at half of the movement duration. For each trajectory, the appropriate synergy weight matrix was computed. The variation of the dimensionality performance index with respect to via-point orientation is obtained, as seen in the polar plot in Figure 10B.

Bottom Line: Dimensionality of various reaching trajectories is compared when using idealized temporal synergies.The results indicate that a trajectory and synergy basis specific DR of behavior results from muscle synergy control.The implications of these results for the synergy hypothesis, optimal motor control, motor development, and robotics are discussed.

View Article: PubMed Central - PubMed

Affiliation: Artificial Intelligence Laboratory, Department of Informatics, University of Zürich Zürich, Switzerland.

ABSTRACT
The muscle synergy hypothesis is an archetype of the notion of Dimensionality Reduction (DR) occurring in the central nervous system due to modular organization. Toward validating this hypothesis, it is important to understand if muscle synergies can reduce the state-space dimensionality while maintaining task control. In this paper we present a scheme for investigating this reduction utilizing the temporal muscle synergy formulation. Our approach is based on the observation that constraining the control input to a weighted combination of temporal muscle synergies also constrains the dynamic behavior of a system in a trajectory-specific manner. We compute this constrained reformulation of system dynamics and then use the method of system balancing for quantifying the DR; we term this approach as Trajectory Specific Dimensionality Analysis (TSDA). We then investigate the consequence of minimization of the dimensionality for a given task. These methods are tested in simulations on a linear (tethered mass) and a non-linear (compliant kinematic chain) system. Dimensionality of various reaching trajectories is compared when using idealized temporal synergies. We show that as a consequence of this Minimum Dimensional Control (MDC) model, smooth straight-line Cartesian trajectories with bell-shaped velocity profiles emerged as the optima for the reaching task. We also investigated the effect on dimensionality due to adding via-points to a trajectory. The results indicate that a trajectory and synergy basis specific DR of behavior results from muscle synergy control. The implications of these results for the synergy hypothesis, optimal motor control, motor development, and robotics are discussed.

No MeSH data available.