Evidence for cutaneous and corticospinal modulation of presynaptic inhibition of Ia afferents from the human lower limb

  • Iles J
  • 83

    Readers

    Mendeley users who have this article in their library.
  • 143

    Citations

    Citations of this article.

Abstract

1. Presynaptic inhibition of soleus muscle I a afferent fibres, produced by stimulation of group I afferents in the common peroneal nerve, was assessed from changes in the H reflex at long conditioning intervals, in six normal subjects. 2. Stimulation of the ipsilateral sural nerve at the malleolus, just before stimulation of the common peroneal nerve at the head of the fibula, decreased the presynaptic inhibition. This effect was strongest during voluntary plantar flexion and weaker during dorsiflexion or at rest. 3. Stimulation of other cutaneous nerve branches serving the dorsum of the ipsilateral foot, and also the contralateral sural nerve, decreased presynaptic inhibition. Adequate stimulation of low threshold cutaneous mechanoreceptors by light brushing of both distal dorsal and plantar surfaces of the ipsilateral foot decreased presynaptic inhibition. 4. Stimulation of the ipsilateral plantar nerves increased presynaptic inhibition, but this action is attributed to activation of group I afferents from the intrinsic muscles of the foot. 5. Transcranial magnetic stimulation of the lower limb area of the contralateral motor cortex decreased presynaptic inhibition. This effect was strongest during voluntary plantar flexion and weaker during dorsiflexion or at rest. 6. The actions of cutaneous and corticospinal pathways completely occluded each other. However, when both effects were adjusted to be liminal, a spatial facilitation between them was observed. 7. It is concluded that in man, as in the cat, cutaneous and corticospinal axons converge on interneurones that inhibit the machinery of presynaptic inhibition of group I a afferents. These actions may be responsible for the modulation of presynaptic inhibition which has been observed to precede and accompany a wide range of human movements. The control of motoneuronal excitability by muscle spindle I a afferents is a fundamental feature of organization in the segmental motor system of vertebrates. In the cat, mono-synaptic excitatory projections are very precisely focused onto homonymous motoneurones and heteronymous moto-neurones where the muscles are close synergists, with other connections being infrequent (see Hultborn & Illert, 1991). Transmission between Ia afferents and motoneurones is under presynaptic inhibitory control (Rudomin, 1990). Presynaptic inhibition is stimulated by activity in group I a and I b afferents from many muscles ranging from close synergists to those acting at distant joints. The only discernible pattern in this action is that flexor group I afferents are more potent than those from extensors, and that extensor I a afferents receive more presynaptic

Get free article suggestions today

Mendeley saves you time finding and organizing research

Sign up here
Already have an account ?Sign in

Find this document

Authors

  • J. F. Iles

Cite this document

Choose a citation style from the tabs below

Save time finding and organizing research with Mendeley

Sign up for free