Figure 1.
Chronic PT stimulation or injury alone increase the strength of ipsilateral connections, which were further strengthened by combined injury and stimulation. A, Schematic model of CS termination field in the normal cervical spinal cord (Control) and the changes in termination density after PT lesion (Injured). Blue axons derive from the intact PT; red axons derive from the injured PT; pink shading in injured CS shows the former position of the lesioned axons. B, Ratios of ipsilateral current threshold to contralateral current threshold (Ipsilateral/Contral Threshold Ratio) needed to evoke responses in the deep branch of the radial nerve to PT stimulus trains of two, three, five, and eight pulses. A lower value in the ipsilateral–contralateral ratio indicates augmented access to ipsilateral spinal motor circuits. C, Summary graph showing percentage change in ipsilateral–contralateral threshold ratio. The values for each group were calculated from an average threshold response to all stimulus train lengths. Stimulation (Stim) and injury alone both show increased enhanced capacity to evoke ipsilateral motor responses, which is augmented further in the combined condition (Stim+Inj).
