Muscle synergy patterns as physiological markers of motor cortical damage

Abstract

The experimental findings herein reported are aimed at gaining a perspective on the complex neural events that follow lesions of the motor cortical areas. Cortical damage, whether by trauma or stroke, interferes with the flow of descending signals to the modular interneuronal structures of the spinal cord. These spinal modules subserve normal motor behaviors by activating groups of muscles as individual units (muscle synergies). Damage to the motor cortical areas disrupts the orchestration of the modules, resulting in abnormal movements. To gain insights into this complex process, we recorded myoelectric signals from multiple upper-limb muscles in subjects with cortical lesions. We used a factorization algorithm to identify the muscle synergies. Our factorization analysis revealed, in a quantitative way, three distinct patterns of muscle coordination-including preservation, merging, and fractionation of muscle synergies-that reflect the multiple neural responses that occur after cortical damage. These patterns varied as a function of both the severity of functional impairment and the temporal distance from stroke onset. We think these muscle-synergy patterns can be used as physiological markers of the status of any patient with stroke or trauma, thereby guiding the development of different rehabilitation approaches, as well as future physiological experiments for a further understanding of postinjury mechanisms of motor control and recovery.motor primitive | electromyography | neurorehabilitation | nonnegative matrix factorization | Virtual Reality Rehabilitation System

Muscle synergies after stroke are correlated with perilesional high gamma

“…His pattern was very similar to a recently studied cohort of stroke subjects, where newly formed abnormal synergies were also observed 6. However, another study found that synergies in the affected arm of severely impaired patients could be derived by merging and fractionation of synergies calculated in the unaffected upper‐limb, that is, new synergies were not evident 5. A possible reason for differences may be the neuroanatomical site of the lesion; stroke subjects with intact sensorimotor cortex have been found to have less similar synergies relative to the unaffected limb 16.…”

“…These synergies can be measured by creating lower dimensional representations of electromyography (EMG) signals. After stroke, however, there is a distinct change in the modular recruitment of muscles, thus resulting in abnormal synergies in the most impaired subjects 4, 5, 6. While the neural basis of such abnormal synergies is poorly understood, a commonly held view is that descending cortical inputs can shape subcortical circuits to organize and dynamically control the weighting of synergies 7.…”

Modular control during incline and level walking in humans

“…A flexible temporal recruitment of motor primitives, as well as a flexible modification of the motor modules within each element, is used to achieve stable locomotion adapted to the mechanical demand during walking. Although there are several studies investigating clinical outcomes using the muscle synergies concept in the diagnosis and rehabilitation of pathologies, for example, in stroke (Cheung et al, 2012) and Parkinson's disease (Falaki et al, 2016), a direct translation to training and rehabilitation procedures is still limited. In the future, a better understanding of neuromuscular mechanisms through the analysis of muscle synergies may help to reliably identify motor control strategies, which is essential to improve the specificity of training and rehabilitation protocols in healthy and pathological population.…”

Muscle co-contraction patterns in robot-mediated force field learning to guide specific muscle group training

“…Cheung (Cheung et al, 2012) has outlined three possible strategies of change in muscle synergies after stroke.…”