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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.


Related in: MedlinePlus

Physical systems employed for demonstrating the TSDA. (A) Tethered mass (linear): motion of the mass is constrained to a 2D plane. The mass is anchored to the origin by weak passive forces and actuator forces are applied in two orthogonal directions. (B) Two-link planar compliant kinematic chain (non-linear): end-point motion is constrained to a 2D surface. Passive joint stiffness and damping effects are present and joint torques are used to actuate the system. The state-space descriptions of these systems have identical input (2), state (4), and output (2) dimensionality.
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Figure 2: Physical systems employed for demonstrating the TSDA. (A) Tethered mass (linear): motion of the mass is constrained to a 2D plane. The mass is anchored to the origin by weak passive forces and actuator forces are applied in two orthogonal directions. (B) Two-link planar compliant kinematic chain (non-linear): end-point motion is constrained to a 2D surface. Passive joint stiffness and damping effects are present and joint torques are used to actuate the system. The state-space descriptions of these systems have identical input (2), state (4), and output (2) dimensionality.

Mentions: This system consists of a point mass constrained to move in a 2D plane as seen in Figure 2A. It is “tethered” to an origin by weak passive forces using linear springs and is subject to visco-elastic damping. The system can be actuated by independent forces in two orthogonal directions, and the output describes the position in the 2D space relative to the origin. The dynamics of this system are described by,


Do muscle synergies reduce the dimensionality of behavior?

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

Physical systems employed for demonstrating the TSDA. (A) Tethered mass (linear): motion of the mass is constrained to a 2D plane. The mass is anchored to the origin by weak passive forces and actuator forces are applied in two orthogonal directions. (B) Two-link planar compliant kinematic chain (non-linear): end-point motion is constrained to a 2D surface. Passive joint stiffness and damping effects are present and joint torques are used to actuate the system. The state-space descriptions of these systems have identical input (2), state (4), and output (2) dimensionality.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Physical systems employed for demonstrating the TSDA. (A) Tethered mass (linear): motion of the mass is constrained to a 2D plane. The mass is anchored to the origin by weak passive forces and actuator forces are applied in two orthogonal directions. (B) Two-link planar compliant kinematic chain (non-linear): end-point motion is constrained to a 2D surface. Passive joint stiffness and damping effects are present and joint torques are used to actuate the system. The state-space descriptions of these systems have identical input (2), state (4), and output (2) dimensionality.
Mentions: This system consists of a point mass constrained to move in a 2D plane as seen in Figure 2A. It is “tethered” to an origin by weak passive forces using linear springs and is subject to visco-elastic damping. The system can be actuated by independent forces in two orthogonal directions, and the output describes the position in the 2D space relative to the origin. The dynamics of this system are described by,

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.


Related in: MedlinePlus