Cervical and thoracolumbar transspinal stimulation at 0.3 Hz and 30 Hz facilitates neuronal excitability in healthy humans: A randomized cross-over study

Effective neuromodulation protocols for upper motor neuron lesions are in great need. Based on the significant role of intraspinal neuronal pathways in motor control, we investigated here the effects of multisite cervical and thoracolumbar transspinal stimulation on arm and leg corticospinal and spinal reflex excitability. Ten healthy subjects were randomly assigned to receive multisite transspinal stimulation at either 0.3 or 30 Hz. Stimulation at either frequency was delivered at alternating subthreshold and suprathreshold intensities in blocks of 10 minutes for 40 minutes total. Before and after multisite transspinal stimulation, the flexor carpi radialis (FCR) and right tibialis anterior (TA) motor evoked potentials, and the soleus M-wave and H-reflex recruitment curves were assembled. Multisite cervical and thoracolumbar transspinal stimulation at 0.3 and/or 30 Hz increased corticospinal excitability for both upper and lower extremity. A shift to the left was evident for the soleus H-reflex recruitment curve only with multisite transspinal stimulation at 30 Hz, which supports for changes in the recruitment order of soleus motoneurons. These findings suggest that multisite transspinal stimulation along the neural axis increases the excitability state of distributed corticospinal neuronal networks and can be beneficial for recovery of weak corticospinal control of arms and legs as is the case in upper motoneuron lesions in humans.