Fig. 4. Original tracings of the conditioned and unconditioned H reflex during control conditions and 0.8 vol% sevoflurane. The conditioning stimulus leads to an increase of the H-reflex amplitude (  dotted line ) in comparison with the unconditioned H-reflex amplitude (  continuous line ). During sevoflurane administration, the H reflex was adjusted so that the amplitude of the unconditioned H reflex was of the same size as during control conditions. The conditioning volley of the femoral nerve was kept constant during both conditions. During control conditions, the conditioning volley leads to a greater increase (facilitation) of the H reflex than during 0.8 vol% sevoflurane (  dotted line ),  i.e. , the heteronymous Ia facilitation of the soleus H reflex is suppressed by sevoflurane. The amount of facilitation is calculated as the increase (%) of H-reflex amplitude due to the conditioning stimulus.