Origins of Common Neural Inputs to Different Compartments of the Extensor Digitorum Communis Muscle

Chenyun Dai,Xiaogang Hu,Henry Shin,Bradley Davis

doi:10.1038/s41598-017-14555-x

Abstract

The extensor digitorum communis (EDC) is a multi-compartment muscle that allows dexterous extension of the four digits. However, the level of common input shared across different compartments of this muscle is not well understood. We seek to systematically characterize the common and independent neural input, originated from different levels of the central nervous system, to the different compartments. A motor unit (MU) coherence analysis was used to capture the different sources of common and independent input, by quantifying the coherence of MU discharge between different compartments. The MU activities were obtained from decomposition of surface electromyogram recordings. Our results showed that the MU coherence across different muscle compartments accounted for only a small proportion (<20%) of the total input in the alpha (5–12 Hz) and beta (15–30 Hz) bands, but was a major driver (>60%) in the delta (1–4 Hz) band. Additionally, cross-compartment coherence between the middle and ring-little fingers tended to be higher as compared with other finger combinations. Overall, the common input shared across different fingers are found to be at low to moderate levels, in comparison with the total input, which allows dexterous control of individual digits with some degree of coordinated control of multiple digits.

Highlights

Earlier studies have focused on the estimation of the time-domain common input within a muscle[8,9]
A coherence analysis of motor unit (MU) discharge events was used to quantify the relative contribution of shared vs. separate neural input to the different compartments, and the different origins of common input can be characterized based on the coherence level in each previously defined frequency bandwidth
Our results reveal a low level (60% of the total common drive) level of shared input in the delta band, admittedly the definition of the different levels was rather arbitrary

Summary

Introduction

Earlier studies have focused on the estimation of the time-domain common input within a muscle[8,9]. The relative contribution between shared and separated common drive has not been systematically quantified during EDC muscle activation To address this issue, we adopted a MU discharge coherence analysis[11,12,13,14] in the frequency-domain, in order to capture the different origins of common neural input both within and across compartments of the EDC muscle. Our main findings reveal that the shared common input across different compartment pairs of the EDC only involve a small portion (60%) to the total neural drive during common modulation of the firing rate. We found that the shared common input between the middle and ring-little fingers was higher than any other pairs, indicating less independent control of middle and ring-little fingers

Objectives

Results

Conclusion