Effects of high-dose TRH on the vibratory inhibition of soleus H-reflex have 
been studied in 9 patients with amyotrophic lateral sclerosis. In 6 of the 9, 
TRH induced a significant increase in vibratory inhibition. This suggests that 
the TRH-induced reduction of spasticity might be due to an increase in 
presynaptic inhibition acting on Ia fibres.