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This study assessed whether changes in size or time- course of excitatory po stsynaptic potentials (EPSPs) in motoneurons innervating spastic muscle could in duce a greater synaptic response, and thereby contribute to reflex hyperexcitabi lity. We compared motor unit (MU) firing patterns elicited by tendon taps applie d to both spastic and contralateral (nonspastic) biceps brachii muscle in hemipa retic stroke subjects. Based on recordings of 115 MUs, significantly shortened E PSP rise times were present on the spastic side, but with no significant differe nces in estimated EPSP amplitude. These changes may contribute to hyperexcitable reflex responses at short latency, but the EPSP amplitude changes appear insuff icient to account for global differences in reflex excitability.
This study organized whether changes in size or time-course of excitatory po stsynaptic potentials (EPSPs) in motoneurons innervating spastic muscle could in duce a greater synaptic response, and so contribute to reflex hyperexcitabi lity. We compared motor unit (MU) firing patterns elicited by tendon taps applie d to both spastic and contralateral (nonspastic) biceps brachii muscle in hemipa retic stroke subjects. Based on recordings of 115 MUs, significantly shortened E PSP rise times were present on the spastic side, with no significant differences in estimated EPSP amplitude. These changes may contribute to hyperexcitable reflex responses at short latency, but the EPSP amplitude changes appear insuff icient to account for global differences in reflex excitability.