scholarly journals Investigating the Effect of Persistent Inward Currents on Motor Unit Firing Rates and Beta-Band Coherence in a Model of the First Dorsal Interosseous Muscle*

2019 ◽  
Author(s):  
Sageanne Senneff ◽  
Lara McManus ◽  
Madeleine M. Lowery
Keyword(s):  
Motor Unit ◽  
First Dorsal Interosseous ◽  
Beta Band ◽  
Persistent Inward Currents ◽  
Firing Rates ◽  
Motor Unit Firing ◽  
First Dorsal Interosseous Muscle ◽  
Inward Currents ◽  
Dorsal Interosseous Muscle

scholarly journals Beta-band motor unit coherence and nonlinear surface EMG features of the first dorsal interosseous muscle vary with force

2019 ◽  
Vol 122 (3) ◽  
pp. 1147-1162 ◽  
Author(s):  
Lara McManus ◽  
Matthew W. Flood ◽  
Madeleine M. Lowery
Keyword(s):  
Motor Unit ◽  
Motor Units ◽  
Surface Emg ◽  
Sample Entropy ◽  
Beta Band ◽  
Motoneuron Pool ◽  
Motor Unit Firing ◽  
First Dorsal Interosseous Muscle ◽  
Nonlinear Surface ◽  
Dorsal Interosseous Muscle

Motor unit firing times are weakly coupled across a range of frequencies during voluntary contractions. Coherent activity within the beta-band (15–35 Hz) has been linked to oscillatory cortical processes, providing evidence of functional connectivity between the motoneuron pool and motor cortex. The aim of this study was to investigate whether beta-band motor unit coherence is altered with increasing abduction force in the first dorsal interosseous muscle. Coherence between motor unit firing times, extracted from decomposed surface electromyography (EMG) signals, was investigated in 17 subjects at 10, 20, 30, and 40% of maximum voluntary contraction. Corresponding changes in nonlinear surface EMG features (specifically sample entropy and determinism, which are sensitive to motor unit synchronization) were also examined. A reduction in beta-band and alpha-band coherence was observed as force increased [ F(3, 151) = 32, P < 0.001 and F(3, 151) = 27, P < 0.001, respectively], accompanied by corresponding changes in nonlinear surface EMG features. A significant relationship between the nonlinear features and motor unit coherence was also detected ( r = −0.43 ± 0.1 and r = 0.45 ± 0.1 for sample entropy and determinism, respectively; both P < 0.001). The reduction in beta-band coherence suggests a change in the relative contribution of correlated and uncorrelated presynaptic inputs to the motoneuron pool, and/or a decrease in the responsiveness of the motoneuron pool to synchronous inputs at higher forces. The study highlights the importance of considering muscle activation when investigating changes in motor unit coherence or nonlinear EMG features and examines other factors that can influence coherence estimation. NEW & NOTEWORTHY Intramuscular alpha- and beta-band coherence decreased as muscle contraction force increased. Beta-band coherence was higher in groups of high-threshold motor units than in simultaneously active lower threshold units. Alterations in motor unit coherence with increases or decreases in force and with the onset of fatigue were accompanied by corresponding changes in surface electromyography sample entropy and determinism. Mixed-model analysis indicated mean firing rate and number of motor units also influenced the coherence estimate.

scholarly journals Sex-related differences in motor unit firing rates and action potential amplitudes of the first dorsal interosseous during high-, but not low-intensity contractions

2020 ◽  
Vol 238 (5) ◽  
pp. 1133-1144
Author(s):  
Mandy E. Parra ◽  
Adam J. Sterczala ◽  
Jonathan D. Miller ◽  
Michael A. Trevino ◽  
Hannah L. Dimmick ◽  
...  
Keyword(s):  
Action Potential ◽  
Motor Unit ◽  
First Dorsal Interosseous ◽  
Firing Rates ◽  
Low Intensity ◽  
Motor Unit Firing

scholarly journals Muscle fatigue increases beta-band coherence between the firing times of simultaneously active motor units in the first dorsal interosseous muscle

2016 ◽  
Vol 115 (6) ◽  
pp. 2830-2839 ◽  
Author(s):  
Lara McManus ◽  
Xiaogang Hu ◽  
William Z. Rymer ◽  
Nina L. Suresh ◽  
Madeleine M. Lowery
Keyword(s):  
Motor Units ◽  
Surface Emg ◽  
Relative Increase ◽  
Wavelet Coherence ◽  
First Dorsal Interosseous ◽  
Beta Band ◽  
Indirect Measures ◽  
First Dorsal Interosseous Muscle ◽  
Active Motor ◽  
Dorsal Interosseous Muscle

Synchronization between the firing times of simultaneously active motor units (MUs) is generally assumed to increase during fatiguing contractions. To date, however, estimates of MU synchronization have relied on indirect measures, derived from surface electromyographic (EMG) interference signals. This study used intramuscular coherence to investigate the correlation between MU discharges in the first dorsal interosseous muscle during and immediately following a submaximal fatiguing contraction, and after rest. Coherence between composite MU spike trains, derived from decomposed surface EMG, were examined in the delta (1–4 Hz), alpha (8–12 Hz), beta (15–30 Hz), and gamma (30–60 Hz) frequency band ranges. A significant increase in MU coherence was observed in the delta, alpha, and beta frequency bands postfatigue. In addition, wavelet coherence revealed a tendency for delta-, alpha-, and beta-band coherence to increase during the fatiguing contraction, with subjects exhibiting low initial coherence values displaying the greatest relative increase. This was accompanied by an increase in MU short-term synchronization and a decline in mean firing rate of the majority of MUs detected during the sustained contraction. A model of the motoneuron pool and surface EMG was used to investigate factors influencing the coherence estimate. Simulation results indicated that changes in motoneuron inhibition and firing rates alone could not directly account for increased beta-band coherence postfatigue. The observed increase is, therefore, more likely to arise from an increase in the strength of correlated inputs to MUs as the muscle fatigues.

scholarly journals Sensitivity of the paired motor unit analysis for estimation of motoneuron excitability to commonly used constraints and filters

2019 ◽  
Author(s):  
Altamash Hassan ◽  
Christopher K. Thompson ◽  
Francesco Negro ◽  
Mark Cummings ◽  
Randy Powers ◽  
...  
Keyword(s):  
Motor Unit ◽  
Task Demands ◽  
Time Difference ◽  
Motor Deficits ◽  
Persistent Inward Currents ◽  
Firing Rates ◽  
Smoothing Filter ◽  
Motoneuron Excitability ◽  
Inward Currents ◽  
Unit Analysis

AbstractThe nervous system has a tremendous ability to modify motoneuron excitability according to task demands through neuromodulatory synaptic input to motoneurons. Neuromodulatory inputs adjust the response of the motoneuron to excitatory and inhibitory ionotropic input and can facilitate the induction of persistent inward currents (PICs). PICs amplify and prolong the motoneuron response to synaptic inputs, and PIC impairment may play a major role in motor deficits observed in pathological conditions. Noninvasive estimation of the magnitude of neuromodulatory input and persistent inward currents in human motoneurons is achieved through a paired motor unit analysis (ΔF) that quantifies hysteresis in the firing rates at motor unit recruitment and derecruitment. While the ΔF technique is commonly used for estimating motoneuron excitability, computational parameters used for the technique vary across studies. In the present study, we assessed the sensitivity of the ΔF technique to several criteria commonly used in selecting motor unit pairs for analysis, as well as to methods used for smoothing the instantaneous motor unit firing rates. Using HD-sEMG and motor unit decomposition we obtained 5,409 motor unit pairs from the triceps brachii of ten healthy individuals during submaximal triangle contractions. The mean (SD) ΔF was 4.9 (1.08) pps, consistent with previous work using intramuscular recordings. There was an exponential plateau relationship between ΔF and the recruitment time difference between the motor unit pairs, with the plateau occurring at approximately 1 s. There was an exponential decay relationship between ΔF and the derecruitment time difference between the motor unit pairs, with the decay stabilizing at approximately 1.5 s. We found that reducing or removing the minimum threshold for the correlation of the rate-rate slope for the two units did not affect ΔF values or variance. Additionally, we found that removing motor unit pairs in which the control unit was saturated had no significant effect on ΔF. Smoothing filter selection had no substantial effect on ΔF values and ΔF variance; however, the length and type of smoothing filter affected the minimum recruitment and derecruitment time differences. Our results facilitate interpretation of findings from studies that implement the ΔF approach but use different computational parameters.

Sign in / Sign up

Export Citation Format

Share Document