Analysis of the effects of firing rate and synchronization on spike-triggered averaging of multidirectional motor unit torque |
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Authors: | Jason J Kutch Nina L Suresh Anthony M Bloch William Z Rymer |
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Institution: | (1) Department of Mathematics, University of Michigan, Ann Arbor, MI 48109, USA;(2) Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL 60611, USA |
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Abstract: | Spike-triggered averaging (STA) of muscle force transients has often been used to estimate motor unit contractile properties,
using the discharge of a motor unit within the muscle as the triggering events. For motor units that exert torque about multiple
degrees-of-freedom, STA has also been used to estimate motor unit pulling direction. It is well known that motor unit firing
rate and weak synchronization of motor unit discharges with other motor units in the muscle can distort STA estimates of contractile
properties, but the distortion of STA estimates of motor unit pulling direction has not been thoroughly evaluated. Here, we
derive exact equations that predict that STA decouples firing rate and synchronization distortion when used to estimate motor
unit pulling direction. We derive a framework for analyzing synchronization, consider whether the distortion due to synchronization
can be removed from STA estimates of pulling direction, and show that there are distributions of motor unit pulling directions
for which STA is insensitive to synchronization. We conclude that STA may give insight into how motoneuronal synchronization
is organized with respect to motor unit pulling direction.
Action Editor: David Terman |
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Keywords: | Spike-triggered averaging Motor unit Pulling direction Firing rate Synchronization |
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