Evidence for presynaptic inhibition of muscle spindle Ia afferents in man

A new method for estimating presynaptic inhibition of soleus (Sol) Ia fibres in man is introduced based on the assessment of the amount of facilitation produced by a preceding homonymous Ia volley onto a Sol monosynaptic reflex. It was found in animal experiments that a reduction of such Ia facilitation reflects the amount of presynaptic inhibition exerted on these Ia fibres. Since, in man, a similar reduction of homonymous Ia facilitation was found after tibialis anterior vibration, this provides evidence for presynaptic inhibition of Sol Ia fibres, elicited here by the afferent discharge due to this flexor vibration.