Reflex effects from Golgi tendon organ (Ib) afferents are unchanged after spinal cord lesions in humans

The reflex actions of medial gastrocnemius (MG) group I afferents on soleus motoneurons were examined in 20 normal subjects and 13 patients with well-defined chronic spinal cord lesions. In normal subjects, stimulation of the MG nerve with near-nerve electrodes at or below the threshold of the alpha motoneuron axons resulted in inhibition of the soleus H reflex at a condition-test interval of 6 msec. The central delay was estimated to be 2.5 msec. This inhibition was attributed to Ib afferents. We found that this inhibition was present in patients with spinal cord lesions. This contrasts with previous reports that stimulation of MG afferents facilitates the soleus H reflex in hemiplegic limbs, and it may represent a physiologic difference between cerebral and spinal spasticity.