HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Mattei, B. Articles by Schmied, A. Search for Related Content PubMed PubMed Citation Articles by Mattei, B. Articles by Schmied, A.

Delayed and prolonged effects of a near threshold EPSP on the firing time of human -motoneurones

Benjamin Mattei and Annie Schmied

In order to investigate the effects of near-threshold excitatory inputs on the precise timing of the action potentials during the tonic discharge of human motoneurones, the activity of single motor units was recorded in the extensor carpi radialis muscles while tendon taps (indentation, 0.1 mm; duration, 1 ms) were being delivered irregularly at a mean rate of 0.8 s^-1. New methods of analysis, such as the phase response function, were used to study the relative changes in the interspike interval (ISI₁) during which the stimulus was being delivered and in the three subsequent intervals (ISI₂, ISI₃, ISI₄) as a percentage of the pre-stimulus interspike interval (ISI₀). The consistency of the effects of the actual stimulus as regards the spontaneous variability was assessed by comparing the data with those obtained with virtual stimulation. When the stimulus occurred at the end of ISI₁, and triggered a spike, ISI₁ and ISI₃ were generally shortened, whereas ISI₂ was lengthened, probably due to the negative correlation induced by the summation of the after-hyperpolarisations (AHPs). When the stimulus occurred in the middle of ISI₁ without triggering a spike, ISI₁, ISI₂ and more rarely ISI₃ were shortened. Lastly, when the stimulus occurred during the AHP scoop in ISI₁, ISI₂ was shortened although ISI₁ remained unchanged. ISI₄ was not consistently affected in any of these cases. The present results show that the tendon tap-induced inputs (probably from muscle spindle primary endings) mediated delayed and prolonged shortening effects of the ISIs on most of the -motoneurones tested (n = 16). These effects undetected in classic peri-stimulus histogram analysis may involve long-lasting conductance changes although the contribution of polysynaptic pathways cannot be excluded. The changes in ISI were quite moderate (< 15 % of ISI) but highly consistent. Their functional involvement in the synchronisation or desynchronisation processes and/or the mechanisms of optimisation of muscle contraction still remains to be explored.

This article has been cited by other articles:

				J. G. Mancilla, T. J. Lewis, D. J. Pinto, J. Rinzel, and B. W. Connors Synchronization of Electrically Coupled Pairs of Inhibitory Interneurons in Neocortex J. Neurosci., February 21, 2007; 27(8): 2058 - 2073. [Abstract] [Full Text] [PDF]

				B. S. Gutkin, G. B. Ermentrout, and A. D. Reyes Phase-Response Curves Give the Responses of Neurons to Transient Inputs J Neurophysiol, August 1, 2005; 94(2): 1623 - 1635. [Abstract] [Full Text] [PDF]

				Y. Prut and S. I. Perlmutter Firing Properties of Spinal Interneurons during Voluntary Movement. I. State-Dependent Regularity of Firing J. Neurosci., October 22, 2003; 23(29): 9600 - 9610. [Abstract] [Full Text] [PDF]