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Motor Unit Discharge Variability Is Increased in Mild-To-Moderate Parkinson's Disease

Individuals with Parkinson's disease (PD) demonstrate deficits in muscle activation such as decreased amplitude and inappropriate bursting. There is evidence that some of these disturbances are more pronounced in extensor vs. flexor muscles. Surface EMG has been used widely to quantify muscle a...

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Autores principales: Wilson, Jessica M., Thompson, Christopher K., McPherson, Laura Miller, Zadikoff, Cindy, Heckman, C.J., MacKinnon, Colum D.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Frontiers Media S.A. 2020
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7272659/
https://www.ncbi.nlm.nih.gov/pubmed/32547482
http://dx.doi.org/10.3389/fneur.2020.00477
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author Wilson, Jessica M.
Thompson, Christopher K.
McPherson, Laura Miller
Zadikoff, Cindy
Heckman, C.J.
MacKinnon, Colum D.
author_facet Wilson, Jessica M.
Thompson, Christopher K.
McPherson, Laura Miller
Zadikoff, Cindy
Heckman, C.J.
MacKinnon, Colum D.
author_sort Wilson, Jessica M.
collection PubMed
description Individuals with Parkinson's disease (PD) demonstrate deficits in muscle activation such as decreased amplitude and inappropriate bursting. There is evidence that some of these disturbances are more pronounced in extensor vs. flexor muscles. Surface EMG has been used widely to quantify muscle activation deficits in PD, but analysis of discharge of the underlying motor units may provide greater insight and be more sensitive to changes early in the disease. Of the few studies that have examined motor unit discharge in PD, the majority were conducted in the first dorsal interosseous, and no studies have measured motor units from extensor and flexor muscles within the same cohort. The objective of this study was to characterize the firing behavior of single motor units in the elbow flexor and extensor muscles during isometric contractions in people with mild-to-moderate PD. Ten individuals with PD (off-medication) and nine healthy controls were tested. Motor unit spike times were recorded via intramuscular EMG from the biceps and triceps brachii muscles during 30-s isometric contractions at 10% maximum voluntary elbow flexion and elbow extension torque, respectively. We selected variables of mean motor unit discharge rate, discharge variability, and torque variability to evaluate motor abnormalities in the PD group. The effects of group, muscle, and group-by-muscle on each variable were determined using separate linear mixed models. Discharge rate and torque variability were not different between groups, but discharge variability was significantly higher in the PD group for both muscles combined (p < 0.0001). We also evaluated the asymmetry in these motor variables between the triceps and biceps for each individual participant with PD to evaluate whether there was an association with disease severity. The difference in torque variability between elbow flexion and extension was significantly correlated with both the Hoehn and Yahr scale (rho = 0.71) and UPDRS (rho = 0.62). Our findings demonstrate that variability in motor output, rather than decreased discharge rates, may contribute to motor dysfunction in people with mild-to-moderate PD. Our findings provide insight into altered neural control of movement in PD and demonstrate the importance of measuring from multiple muscles within the same cohort.
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spelling pubmed-72726592020-06-15 Motor Unit Discharge Variability Is Increased in Mild-To-Moderate Parkinson's Disease Wilson, Jessica M. Thompson, Christopher K. McPherson, Laura Miller Zadikoff, Cindy Heckman, C.J. MacKinnon, Colum D. Front Neurol Neurology Individuals with Parkinson's disease (PD) demonstrate deficits in muscle activation such as decreased amplitude and inappropriate bursting. There is evidence that some of these disturbances are more pronounced in extensor vs. flexor muscles. Surface EMG has been used widely to quantify muscle activation deficits in PD, but analysis of discharge of the underlying motor units may provide greater insight and be more sensitive to changes early in the disease. Of the few studies that have examined motor unit discharge in PD, the majority were conducted in the first dorsal interosseous, and no studies have measured motor units from extensor and flexor muscles within the same cohort. The objective of this study was to characterize the firing behavior of single motor units in the elbow flexor and extensor muscles during isometric contractions in people with mild-to-moderate PD. Ten individuals with PD (off-medication) and nine healthy controls were tested. Motor unit spike times were recorded via intramuscular EMG from the biceps and triceps brachii muscles during 30-s isometric contractions at 10% maximum voluntary elbow flexion and elbow extension torque, respectively. We selected variables of mean motor unit discharge rate, discharge variability, and torque variability to evaluate motor abnormalities in the PD group. The effects of group, muscle, and group-by-muscle on each variable were determined using separate linear mixed models. Discharge rate and torque variability were not different between groups, but discharge variability was significantly higher in the PD group for both muscles combined (p < 0.0001). We also evaluated the asymmetry in these motor variables between the triceps and biceps for each individual participant with PD to evaluate whether there was an association with disease severity. The difference in torque variability between elbow flexion and extension was significantly correlated with both the Hoehn and Yahr scale (rho = 0.71) and UPDRS (rho = 0.62). Our findings demonstrate that variability in motor output, rather than decreased discharge rates, may contribute to motor dysfunction in people with mild-to-moderate PD. Our findings provide insight into altered neural control of movement in PD and demonstrate the importance of measuring from multiple muscles within the same cohort. Frontiers Media S.A. 2020-05-29 /pmc/articles/PMC7272659/ /pubmed/32547482 http://dx.doi.org/10.3389/fneur.2020.00477 Text en Copyright © 2020 Wilson, Thompson, McPherson, Zadikoff, Heckman and MacKinnon. http://creativecommons.org/licenses/by/4.0/ This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
spellingShingle Neurology
Wilson, Jessica M.
Thompson, Christopher K.
McPherson, Laura Miller
Zadikoff, Cindy
Heckman, C.J.
MacKinnon, Colum D.
Motor Unit Discharge Variability Is Increased in Mild-To-Moderate Parkinson's Disease
title Motor Unit Discharge Variability Is Increased in Mild-To-Moderate Parkinson's Disease
title_full Motor Unit Discharge Variability Is Increased in Mild-To-Moderate Parkinson's Disease
title_fullStr Motor Unit Discharge Variability Is Increased in Mild-To-Moderate Parkinson's Disease
title_full_unstemmed Motor Unit Discharge Variability Is Increased in Mild-To-Moderate Parkinson's Disease
title_short Motor Unit Discharge Variability Is Increased in Mild-To-Moderate Parkinson's Disease
title_sort motor unit discharge variability is increased in mild-to-moderate parkinson's disease
topic Neurology
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7272659/
https://www.ncbi.nlm.nih.gov/pubmed/32547482
http://dx.doi.org/10.3389/fneur.2020.00477
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