Monosynaptic coding of group Ia afferent discharges during vibratory stimulation of muscles.

1. Tonic activation of muscular activity was observed during forced vibration of the gastrocnemius and soleus muscles in the decerebrate cat. Such tonic activity was not observed in the tibialis anterior muscle. 2. Intervals of both unitary EMG and motoneuronal spikes were shown to occur according to the principle of integer multiplication of vibratory cyclic time. 3. Gradual recruitment of tonic vibration reflex (vibratory facilitation) was found to survive after the cessation of vibratory stimulation (postvibratory facilitation). 4. Nonsequential interspikes revealed that gradual tonic recriutment is effected by the spikes with a shorter firing interval. 5. Muscle activities during TVR may be effected by PTP with some excitatory frequency associated with that of the applied vibration. 6. Postvibratory facilitation did not correlate with the vibratory frequency. The firing of such phases may be determined by the intrinsic repetition rate of the individual motoneuron.