Relationship Between Simulated Common Synaptic Input and Discharge Synchrony in Cat Spinal Motoneurons
Department of Physiology and Biophysics, School of Medicine, University of Washington, Seattle, Washington 98195 Binder, Marc D. and Randall K. Powers. Relationship Between Simulated Common Synaptic Input and Discharge Synchrony in Cat Spinal Motoneurons. J. Neurophysiol. 86: 2266-2275, 2001. Synchr...
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Veröffentlicht in: | Journal of neurophysiology 2001-11, Vol.86 (5), p.2266-2275 |
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Zusammenfassung: | Department of Physiology and Biophysics, School of Medicine,
University of Washington, Seattle, Washington 98195
Binder, Marc D. and
Randall K. Powers.
Relationship Between Simulated Common Synaptic Input and
Discharge Synchrony in Cat Spinal Motoneurons. J. Neurophysiol. 86: 2266-2275, 2001. Synchronized
discharge of individual motor units is commonly observed in the muscles
of human subjects performing voluntary contractions. The amount of this
synchronization is thought to reflect the extent to which motoneurons
in the same and related pools share common synaptic input. However, the
relationship between the proportion of shared synaptic input and the
strength of synchronization has never been measured directly. In this
study, we simulated common shared synaptic input to cat spinal
motoneurons by driving their discharge with noisy, injected current
waveforms. Each motoneuron was stimulated with a number of different
injected current waveforms, and a given pair of waveforms were either
completely different or else shared a variable percentage of common
elements. Cross-correlation histograms were then compiled between the
discharge of motoneurons stimulated with noise waveforms with variable
degrees of similarity. The strength of synchronization increased with
the amount of simulated "common" input in a nonlinear fashion.
Moreover, even when motoneurons had >90% of their simulated synaptic
inputs in common, only ~25-45% of their spikes were synchronized.
We used a simple neuron model to explore how variations in neuron
properties during repetitive discharge may lead to the low levels of
synchronization we observed experimentally. We found that small
variations in spike threshold and firing rate during repetitive
discharge lead to large decreases in synchrony, particularly when
neurons have a high degree of common input. Our results may aid in the
interpretation of studies of motor unit synchrony in human hand muscles
during voluntary contractions. |
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ISSN: | 0022-3077 1522-1598 |
DOI: | 10.1152/jn.2001.86.5.2266 |