Non-Linear Discharge of Human Motor Units During Linear Time-Varying Contractions Across Motor Pools

McAuliffe, D.; Kmiec, Tyler; Taylor, Chris; Thompson, Christopher K.

doi:10.1109/spmb50085.2020.9353641

Cited by 2 publications

(2 citation statements)

References 23 publications

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“…Therefore, the maximum magnitude of deviation in discharge rate (referred to here as brace height) from a theoretical linear increase in discharge rate, from recruitment to peak, can be used as a proxy for PIC amplification. Furthermore, given that this maximum deviation is geometrically the point at which the change in discharge rate over time transitions from a trend of steep increase to an attenuated increase, this point can be used to separate and characterize the secondary and tertiary discharge ranges (Afsharipour et al 2020 , Mcauliffe et al 2020 ). The work herein defines the quantification of brace height and these associated metrics; validates and compares these metrics on a simulated motoneuron pool with known excitatory, inhibitory, and neuromodulatory inputs; characterizes these metrics on a large dataset of human MUs; and discusses potential implications and limitations of the approach.…”

Section: Introductionmentioning

confidence: 99%

A geometric approach to quantifying the neuromodulatory effects of persistent inward currents on individual motor unit discharge patterns

et al. 2023

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Objective: All motor commands flow through motoneurons, which entrain control of their innervated muscle fibers, forming a motor unit (MU). Owing to the high fidelity of action potentials within MUs, their discharge profiles detail the organization of ionotropic excitatory/inhibitory as well as metabotropic neuromodulatory commands to motoneurons. Neuromodulatory inputs (e.g., norepinephrine, serotonin) enhance motoneuron excitability and facilitate persistent inward currents (PICs). PICs introduce quantifiable properties in MU discharge profiles by augmenting depolarizing currents upon activation (i.e., PIC amplification) and facilitating discharge at lower levels of excitatory input than required for recruitment (i.e., PIC prolongation). Approach: Here, we introduce a novel geometric approach to estimate neuromodulatory and inhibitory contributions to MU discharge by exploiting discharge non-linearities introduced by PIC amplification during time-varying linear tasks. In specific, we quantify the deviation from linear discharge (“brace height”) and the rate of change in discharge (i.e., acceleration slope, attenuation slope, angle). We further characterize these metrics on a simulated motoneuron pool with known excitatory, inhibitory, and neuromodulatory inputs and on human MUs (Number of MUs; Tibialis Anterior: 1448, Medial Gastrocnemius: 2100, Soleus: 1062, First Dorsal Interosseus: 2296). Main Result: In the simulated motor pool, we found brace height and attenuation slope to consistently indicate changes in neuromodulation and the pattern of inhibition (excitation-inhibition coupling), respectively, whereas the paired MU analysis (ΔF) was dependent on both neuromodulation and inhibition pattern. Furthermore, we provide estimates of these metrics in human MUs and show comparable variability in ΔF and brace height measures for MUs matched across multiple trials. Significance: Spanning both datasets, we found brace height quantification to provide an intuitive method for achieving graded estimates of neuromodulatory and inhibitory drive to individual MUs. This complements common techniques and provides an avenue for decoupling changes in the level of neuromodulatory and pattern of inhibitory motor commands.

show abstract

Section: Introductionmentioning

confidence: 99%

A geometric approach to quantifying the neuromodulatory effects of persistent inward currents on individual motor unit discharge patterns

et al. 2023

View full text Add to dashboard Cite

show abstract

“…Therefore, the maximum magnitude of deviation in discharge rate (referred to here as brace height) from a theoretical linear increase in discharge rate, from recruitment to peak, can be used as a proxy for PIC amplification. Furthermore, given that this maximum deviation is geometrically the point at which the change in discharge rate over time transitions from a trend of steep increase to an attenuated increase, this point can be used to separate and characterize the secondary and tertiary discharge ranges (Afsharipour et al, 2020, D. McAuliffe, 2020. The work herein defines the quantification of brace height and these associated metrics; validates and compares these metrics on a simulated motoneuron pool with known excitatory, inhibitory, and neuromodulatory inputs; characterizes these metrics on a large dataset of human MUs; and discusses potential implications and limitations of the approach.…”

Section: Introductionmentioning

confidence: 99%

A geometric approach to quantifying the neuromodulatory effects of persistent inward currents on single motor unit discharge patterns

Beauchamp¹,

Pearcey

Khurram

et al. 2022

Preprint

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Objective: All motor commands flow through motoneurons, which entrain control of their innervated muscle fibers, forming a motor unit (MU). Owing to the high fidelity of action potentials within MUs, their discharge profiles detail the organization of ionotropic excitatory/inhibitory as well as metabotropic neuromodulatory commands to motoneurons. Neuromodulatory inputs (e.g., norepinephrine, serotonin) enhance motoneuron excitability and facilitate persistent inward currents (PICs). PICs introduce quantifiable properties in MU discharge profiles by augmenting depolarizing currents upon activation (i.e., PIC amplification) and facilitating discharge at lower levels of excitatory input than required for recruitment (i.e., PIC prolongation). Approach: Here, we introduce a novel geometric approach to estimate neuromodulatory and inhibitory contributions to MU discharge through exploiting discharge non-linearities introduced by PIC amplification during time-varying linear tasks. In specific, we quantify the deviation from linear discharge ("brace height") and the rate of change in discharge (i.e., acceleration slope, attenuation slope, angle). We further characterize these metrics on a simulated motoneuron pool with known excitatory, inhibitory, and neuromodulatory inputs and on human MUs (Tibialis Anterior: 1448, Medial Gastrocnemius: 2100, Soleus: 1062, First Dorsal Interosseus: 2296). Main Result: In the simulated motor pool, we found brace height and attenuation slope to consistently indicate changes in neuromodulation and the pattern of inhibition (excitation-inhibition coupling), respectively, whereas the paired MU analysis (ΔF) was dependent on both neuromodulation and inhibition pattern. Furthermore, we provide estimates of these metrics in human MUs and show comparable variability in ΔF and brace height measures in MUs matched across multiple trials. Significance: Spanning both datasets, we found brace height quantification to provide an intuitive method for achieving graded estimates of neuromodulatory and inhibitory drive to MUs on a single unit level. This complements common techniques and provides an avenue for decoupling changes in the level of neuromodulatory and pattern of inhibitory motor commands.

show abstract

Non-Linear Discharge of Human Motor Units During Linear Time-Varying Contractions Across Motor Pools

Cited by 2 publications

References 23 publications

A geometric approach to quantifying the neuromodulatory effects of persistent inward currents on individual motor unit discharge patterns

A geometric approach to quantifying the neuromodulatory effects of persistent inward currents on individual motor unit discharge patterns

A geometric approach to quantifying the neuromodulatory effects of persistent inward currents on single motor unit discharge patterns

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