Figure 3. Time course of amplitude changes of the M- response and H- reflex evoked by electrical stimulation of the tibial nerve in the rat.

Two stimulation patterns were used: continuous bursts of stimuli (solid lines: black – H reflex, grey – M response) or single stimuli (dashed lines: black - H reflex and grey – M response). The averaged responses to the single stimuli consisted of 30 reflexes collected at the beginning of the first and at the end of the last stimulation sessions daily in one animal. The averaged responses to burst of stimuli were collected during 3 min periods at the beginning and the end of every daily session. The strength of stimulation was established near the threshold of activation of the motor fibers, which is higher than that of Ia afferents, therefore stimulation elicited a moderate H-reflex as the majority of Ia fibers are already excited when the direct motor response (M) is at its threshold.