Intrinsic activation of human motoneurons: reduction of motor unit recruitment thresholds by repeated contractions

Journal of Neurophysiology
Monica A GorassiniDavid J Bennett

Abstract

The main purpose of this study was to examine whether facilitation of human motor unit recruitment by repeated voluntary contractions is mediated, in part, by time and activity-dependent increases in the intrinsic excitability of the parent motoneuron. To do this, pairs of tibialis anterior or soleus motor units were recorded during slowly increasing and then decreasing voluntary contractions. The firing rate of the lower-threshold motor unit of the pair (control unit) was used as a measure of effective synaptic excitation (i.e., drive) to the motoneurons. This rate was used to estimate the recruitment threshold of the higher-threshold unit of the pair (test unit). The test unit was repeatedly recruited and de-recruited in a series of contractions, and the interval between the de-recruitment and re-recruitment of the test unit (interactivation interval) was systematically varied between 0.6 and 60 s. An increase in intrinsic excitability of a unit was considered to have occurred if the level of estimated synaptic input (as measured by the firing rate of the control motor unit) needed to recruit a unit was reduced. At short interactivation intervals (1-2 s), the control unit firing frequency was significantly lower when the test...Continue Reading

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Citations

Apr 3, 2008·The Neuroscientist : a Review Journal Bringing Neurobiology, Neurology and Psychiatry·C J HeckmanJenna Schuster
Nov 14, 2008·Journal of Neurophysiology·Dario FarinaRoger M Enoka
Jul 10, 2009·Journal of Neurophysiology·Carol J MottramWilliam Z Rymer
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Apr 4, 2002·Journal of Neurophysiology·Monica GorassiniDavid J Bennett
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Jul 16, 2020·Journal of Neurophysiology·Edward H KimCharles J Heckman

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