Do muscle synergies reduce the dimensionality of behavior?

Area of Science:

• Motor Control
• Computational Neuroscience
• Robotics

Background:

• The muscle synergy hypothesis posits that the central nervous system reduces dimensionality through modular organization.
• Understanding if muscle synergies can reduce state-space dimensionality while preserving task control is crucial for validating this hypothesis.

Purpose of the Study:

• To investigate dimensionality reduction in biological and artificial motor control systems using temporal muscle synergies.
• To quantify the impact of muscle synergies on reducing dynamic behavior complexity.

Main Methods:

• Utilized the temporal muscle synergy formulation to constrain system dynamics.
• Developed Trajectory Specific Dimensionality Analysis (TSDA) using system balancing to quantify dimensionality reduction.
• Simulated on linear (tethered mass) and non-linear (compliant kinematic chain) systems.

Main Results:

• Demonstrated that Minimum Dimensional Control (MDC) using temporal synergies optimizes reaching trajectories, favoring straight-line paths with bell-shaped velocity profiles.
• Showed that dimensionality reduction is specific to the trajectory and the chosen synergy basis.
• Investigated the effect of via-points on trajectory dimensionality.

Conclusions:

• Muscle synergy control inherently leads to trajectory and synergy basis-specific dimensionality reduction.
• Findings support the muscle synergy hypothesis and have implications for optimal motor control, motor development, and robotics.