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Evidence for cutaneous and corticospinal modulation of presynaptic inhibition of Ia afferents from the human lower limb.
Author(s) -
Iles J F
Publication year - 1996
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1996.sp021207
Subject(s) - transcranial magnetic stimulation , stimulation , sural nerve , anatomy , neuroscience , common peroneal nerve , tibial nerve , superficial peroneal nerve , presynaptic inhibition , medicine , inhibitory postsynaptic potential , psychology , ankle , excitatory postsynaptic potential
1. Presynaptic inhibition of soleus muscle Ia 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 Ia 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.