Coding process in human stretch reflex analysed by phase-locked spikes.

The Achilles tendon of man was tapped by triangular pulsatory waves with stimulus intervals from 10 to 100 Hz, while single motor unit spikes were recorded from the soleus muscle. The discharge probability of the motor unit spikes in relation to the triangular taps was analysed by means of cross-correlograms. A summation of the results of cross-correlograms of motor unit spikes with 10--100 Hz taps revealed one prominnet kernel, the primary correlation kernel. From the summated correlograms, it became clear that the mean width of the primary correlation kernel, the correlation time, was 8.3 +/- 2.5 msec. The correlation time is interpreted as representing the time-to-peak of the excitatory postsynaptic potential of an alpha-motoneuron.