Figure 1.

Schematic illustration of cortical control of spinal reflex circuits and spinal interneuronal circuits investigated after 60 sessions of locomotor training in the same SCI subject. The soleus H-reflex evoked by posterior tibial nerve stimulation, tibialis anterior (TA) muscle motor evoked potential (MEP), soleus H-reflex conditioned by subthreshold transcranial magnetic stimulation (TMS) delivered at an optimal site (“hot spot”) for evoking an MEP in the right soleus muscle, soleus H-reflex depression by common peroneal nerve stimulation that is mediated by Ia inhibitory interneurons (Ia INs; reciprocal inhibition), and the reciprocal inhibition conditioned by subthreshold TMS delivered at an optimal site (“hot spot”) for evoking an MEP in the right TA muscle were all investigated in the same patient at rest and/or during assisted stepping after locomotor training. Open triangles indicate excitatory synapses, while the filled circle indicates inhibitory synapses. The cortical control on these spinal circuits is indicated as a synapse that may increase (+) or decrease (−) actions of flexor-extensor α motor neurons and/or Ia inhibitory interneurons.