Fast Oscillatory Commands from the Motor Cortex Can Be Decoded by the Spinal Cord for Force Control

Area of Science:

• Neuroscience
• Motor Control
• Computational Biology

Background:

• Cortical oscillations in beta (13-30 Hz) and gamma (35-70 Hz) bands are observed in motor pathways.
• The role of these fast oscillations in muscle force control is unclear due to the presumed linear transformation of motoneuron inputs and low-pass filtering by muscles.

Purpose of the Study:

• To investigate the impact of high-frequency cortical oscillatory activity on neuromuscular force control.
• To determine if the motoneuron pool can effectively decode and respond to these oscillations.

Main Methods:

• Utilized a biologically inspired mathematical model of the neuromuscular system.
• Simulated the effects of oscillatory inputs in the beta and gamma frequency bands on motoneuron pool activity and subsequent muscle force generation.

Main Results:

• The motoneuron pool exhibited nonlinear behavior, enabling the decoding of high-frequency oscillatory inputs.
• Single-frequency inputs (e.g., beta band) increased steady-state muscle force.
• Amplitude-modulated inputs at a low frequency caused force oscillations at that frequency.
• The underlying mechanism involved the recruitment and derecruitment of motor units.

Conclusions:

• Cortical oscillations at or above the beta band can play a functional role in muscle force control.
• The recruitment and derecruitment of spinal motoneurons allow muscles to respond to these fast cortical oscillations.
• These findings suggest that fast cortical oscillations are not merely epiphenomena but actively contribute to motor control.