F responses were recorded in 6 cases with SSP and in 22 normal controls. The 
present study confirmed that frequency, number of phases, F/M amplitude ratio 
and duration were significantly increased and CV of onset latencies was 
significantly reduced in cases with SSP. After intravenous injection of TRH (2 
mg), all the parameters were altered toward normal sides. It was suggested that 
the hyperexcitability of motor neuron pool in SSP was stabilized by effects of 
TRH on injured pyramidal tracts and consequently abnormalities of F responses 
were improved. The Effect of TRH to correct the abnormal F responses in SSP 
might be consistent with effects of TRH to reduce spasticity in amyotrophic 
lateral sclerosis described previously.