Figure 6. Schematic diagram outlining the possible neural pathways for integration of inputs arising from leg cycling and somatosensory conditioning stimulation on the presumed Ia presynaptic inhibitory pathway.

At the center is a simplified H-reflex pathway illustrating group Ia afferents synapsing with alpha motoneurons (MNs) of the flexor carpi radialis. Ia PSI and excitability of MNs are regulated by central commands and peripheral feedback related to leg cycling (black square). Inputs from the radial (red lightning bolt) and superficial radial nerves (blue lightning bolt) have excitatory and inhibitory connections onto Ia PSI interneurons (gray circle), respectively. The square with dashed line is a possible shared presynaptic pathways integrating locomotor-related inputs and somatosensory conditioning volleys during locomotion. Green lightning bolt: median nerve stimulation (test stimulation for evoking the FCR H-reflex).