Dual effect of response preparation on conditioned H reflex.

The late or intercurrent facilitation of the soleus H reflex recovery cycle was studied during the preparatory period of a visual reaction time task. Response preparation produced three kinds of effect on the conditioned reflex elicited 200 msec before the end of the preparatory period: depression of the conditioned reflex which was maximum at the 150 msec conditioning interval; enhancement of the conditioned reflex which was maximum at the 300 msec conditioning interval; and, when the soleus muscle was involved in the execution of the voluntary response, an additional depression of the conditioned reflex at each conditioning interval. These different effects of response preparation are discussed with reference to the neural mechanisms which are thought to mediate the intercurrent facilitation.