Hemiplegic spasticity: neurophysiologic studies.

The excitability of segmental reflex pathways in normal subjects and in patients with hemiplegia has been examined by conditioning the monosynaptic H reflex with a 200 msec burst of vibration applied to the tendo Achilles. In 6 normal subjects, the burst of vibration produced a short-latency facilitation of soleus motoneurons (attributed to monosynaptic excitation) which was followed by a longer-latency inhibition. A similar response was observed in 8 patients with hemiplegia, but the late inhibition was significantly less. The loss of an inhibitory mechanism may contribute to the exaggerated reflexes observed in patients with hemiplegia.