Recruitment gain of spinal motor neuron pools in cat and human

  • J. B. NielsenEmail author
  • H. Morita
  • R. Wenzelburger
  • G. Deuschl
  • J.-P. Gossard
  • H. Hultborn
Research Article


The output from a motor nucleus is determined by the synaptic input to the motor neurons and their intrinsic properties. Here, we explore whether the source of synaptic inputs to the motor neurons (cats) and the age or post-stroke conditions (humans) may change the recruitment gain of the motor neuron pool. In cats, the size of Ia EPSPs in triceps surae motor neurons (input) and monosynaptic reflexes (MSRs; output) was recorded in the soleus and medial gastrocnemius motor nerves following graded stimulation of dorsal roots. The MSR was plotted against the EPSP thereby obtaining a measure of the recruitment gain. Conditioning stimulation of sural and peroneal cutaneous afferents caused significant increase in the recruitment gain of the medial gastrocnemius, but not the soleus motor neuron pool. In humans, the discharge probability of individual soleus motor units (input) and soleus H-reflexes (output) was performed. With graded stimulation of the tibial nerve, the gain of the motor neuron pool was assessed as the slope of the relation between probability of firing and the reflex size. The gain in young subjects was higher than in elderly subjects. The gain in post-stroke survivors was higher than in age-matched neurologically intact subjects. These findings provide experimental evidence that recruitment gain of a motor neuron pool contributes to the regulation of movement at the final output stage from the spinal cord and should be considered when interpreting changes in reflex excitability in relation to movement or injuries of the nervous system.


Motor neurons Recruitment Cutaneous afferents Ageing Stroke 



This work was supported by grants from the Danish Research Council and The Danish Society of Multiple Sclerosis. This work was funded by the Elsass Fonden (DK) (Grant No. 18-16).


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Department of NeuroscienceUniversity of CopenhagenCopenhagen NDenmark
  2. 2.Center for Health, Safety and Environmental ManagementShinshu UniversityMatsumotoJapan
  3. 3.Department of NeurologyUniversity of KielKielGermany
  4. 4.Groupe de Recherche sur le Système Nerveux Central, Department of NeurosciencesUniversité de MontréalMontrealCanada

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