Motor Control After Human SCI Through Activation of Muscle Synergies Under Spinal Cord Stimulation

Area of Science:

• Neuroscience
• Biomedical Engineering
• Rehabilitation Science

Background:

• Spinal cord stimulation (SCS) shows promise for motor recovery in individuals with motor-complete spinal cord injury (SCI).
• The precise physiological mechanisms by which SCS facilitates motor control in SCI remain largely undetermined.
• Standard muscle synergy extraction methods, like non-negative matrix factorization (NMF), are inadequate for analyzing electromyography (EMG) data from SCI patients undergoing SCS.

Purpose of the Study:

• To investigate the underlying physiological mechanisms of motor recovery in spinal cord injury (SCI) patients utilizing SCS.
• To analyze and compare muscle synergies in SCI patients under SCS with those of healthy individuals during standing.
• To develop and validate a novel algorithm for accurate muscle synergy extraction in SCI patients under SCS.

Main Methods:

• Development of a new algorithm, rShiftNMF, to overcome limitations of standard NMF for extracting muscle synergies from SCI patients under SCS.
• Analysis of muscle synergies in two motor-complete SCI patients during standing with SCS.
• Comparative analysis of muscle synergies between SCI patients under SCS and healthy control subjects.

Main Results:

• The developed rShiftNMF algorithm significantly improves the interpretation of EMG activity and yields more physiologically meaningful muscle synergy features.
• SCI patients demonstrate a significant reliance on muscle synergy activation for generating motor activity.
• Interleaving SCS selectively activates an additional muscle synergy essential for standing in SCI patients.
• Muscle synergies in SCI patients under SCS exhibit substantial differences compared to those in healthy subjects.

Conclusions:

• SCS influences motor function in spinal cord injury (SCI) through the activation of specific muscle synergies.
• The findings provide critical insights into the mechanisms of SCS-mediated motor recovery.
• The rShiftNMF algorithm offers a robust tool for future research in SCI and neuromodulation.