Characteristics of preceding Ia activity on postactivation depression in health and disease

Abstract

Previous activation of the soleus Ia afferents causes a depression in the amplitude of the H-reflex. This mechanism is referred to as postactivation depression (PAD) and is suggested to be presynaptically mediated. With the use of a paired reflex depression paradigm (eliciting two H-reflexes with conditioning- test intervals from 80 ms to 300 ms), PAD was examined in a group of healthy individuals and a group of hemiplegic patients. Healthy individuals showed substantial depression of the test H-reflex at all intervals. Although the patient group showed substantially less depression at all intervals, increasing the interval between the two reflexes sharply reduced the depression. In a separa..