Measurements of excitatory postsynaptic potentials in the stretch reflex of normal subjects and spastic patients

The patellar tendon was tapped by random impulses of triangular waveform and motor unit spikes were recorded from the quadriceps femoris muscle. The cross-correlogram of the taps and the motor unit spikes revealed a primary correlation kernel, the width of which was interpreted as an indicator of the mean time-to-peak of excitatory postsynaptic potentials (EPSPs) elicited monosynaptically in an alpha-motoneurone by the triangular taps. The mean time-to-peak was 7.6 +/- 1.3 ms in normal subjects and 9.0 +/- 1.8 ms in spastic patients (P less than 0.005). The prolonged time-to-peak of EPSP in spastic patients is consistent with the hypothesis that as a result of degeneration of the corticomotoneuronal tract the Ia axons sprout and form more synaptic contacts on distal portions of the dendrites of alpha-motoneurones.