J Neurophysiol. 2019 Nov 20

Transcutaneous spinal cord stimulation of the cervical cord modulates lumbar networks.

Barss TS1, Parhizi B2, Mushahwar VK3.
Author information
University of Alberta, Canada.
Neuroscience and Mental Health Institute, University of Alberta.
Division of Physical Medicine & Rehabilitation, Department of Medicine, University of Alberta, Canada.
IIt has been established that coordinated arm and leg (A&L) cycling facilitates corticospinal drive, modulation of cervico-lumbar connectivity and ultimately improves over-ground walking in people with incomplete spinal cord injury (iSCI) or stroke. This study examined the effect of non-invasive transcutaneous spinal cord stimulation (tSCS) on the modulation of cervico-lumbar connectivity. Thirteen neurologically intact adults participated in the study. The excitability of the Hoffmann (H-) reflex elicited in the soleus muscle was examined under multiple conditions involving either the arms held in a static position or rhythmic arm cycling, while tSCS was applied to either the cervical or lumbar cord. As expected, soleus H-reflex amplitude was significantly suppressed by 19.2 % during arm cycling (without tSCS) relative to arms static (without tSCS). Interestingly, tSCS of the cervical cord with arms static significantly suppressed the soleus H-reflex (-22.9%) while tSCS over the lumbar cord did not suppress the soleus H-reflex (-3.8%). The combination of arm cycling with cervical or lumbar tSCS did not yield additional suppression of the soleus H-reflex beyond that obtained with arm cycling alone or cervical tSCS alone. The results demonstrate that activation of the cervical spinal cord through both rhythmic arm cycling and tonic tSCS significantly modulate the activity of lumbar networks. This highlights the potential for engaging cervical spinal cord networks through tSCS during rehabilitation interventions to enhance cervico-lumbar connectivity. This connectivity is influential in facilitating improvements in walking function after neurological impairment.

H-reflex modulation; cervico-lumbar connectivity; cycling; locomotion; spinal cord injury