Fig. 1.

Study protocol. After learning to walk on the treadmill, each rat was subjected under anesthesia to a midthoracic contusion injury of the right lateral column (LC) at T₉ and was implanted with soleus EMG electrodes and nerve cuff stimulating electrodes 20 days later. At least 56 days after the injury, each rat was exposed to the control mode (i.e., the right soleus H-reflex was simply measured) for 20 days; the H-reflex up- or down-conditioning mode [i.e., reward occurred when the H-reflex was greater (up-conditioning) or smaller (down-conditioning) than a criterion] for 50 days; and the control mode for 79–108 more days. Soleus locomotor EMG, H-reflexes, and kinematics were assessed before and immediately after conditioning and at the end of data collection. The data from days 60–70, 110–120, and 210–220 (indicated by heavy lines) were used to determine initial (i.e., control) H-reflex size, H-reflex size at the end of up- or down-conditioning, and H-reflex size at the end of data collection (i.e., final H-reflex size), respectively.