Spinal circuits can accommodate interaction torques during multijoint limb movements

Area of Science:

• * Neuroscience
• * Biomechanics
• * Motor Control

Background:

• * Multijoint limb movements generate interaction torques between segments.
• * Human movement control compensates for these torques, but the underlying mechanisms are debated.
• * Two hypotheses exist: central prediction via internal models or peripheral feedback via spinal mechanisms.

Purpose of the Study:

• * To investigate if spinal feedback mechanisms alone are sufficient for coordinating multijoint movements and accommodating interaction torques.
• * To test the equilibrium-point hypothesis's claim of simple descending signals and spinal feedback coordination.

Main Methods:

• * Development of a minimal computational model simulating a two-joint arm.
• * Control of the simulated arm by spinal neural circuitry.
• * Biomechanics simulation to analyze muscle activation patterns and interaction force accommodation.

Main Results:

• * The model successfully transformed simple descending control signals into muscle activations.
• * These activations effectively accommodated interaction forces based on their direction and magnitude.
• * This occurred without relying on central predictive signals or internal models of dynamics.

Conclusions:

• * Peripheral feedback mechanisms, coordinated by spinal circuitry, can manage intersegmental interaction torques.
• * This supports the plausibility of controlling multijoint movements without explicit internal models of dynamics.
• * Suggests simpler descending motor commands may be sufficient for complex movements.