Abstract
Neuronal control of stepping movement in healthy human is based on integration between brain, spinal neuronal networks, and sensory signals. It is generally recognized that there are continuously occurring adjustments in the physiological states of supraspinal centers during all routines movements. For example, visual as well as all other sources of information regarding the subject's environment. These multimodal inputs to the brain normally play an important role in providing a feedforward source of control. We propose that the brain routinely uses these continuously updated assessments of the environment to provide additional feedforward messages to the spinal networks, which provides a synergistic feedforwardness for the brain and spinal cord. We tested this hypothesis in 8 non-injured individuals placed in gravity neutral position with the lower limbs extended beyond the edge of the table, but supported vertically, to facilitate rhythmic stepping. The experiment was performed while visualizing on the monitor a stick figure mimicking bilateral stepping or being motionless. Non-invasive electrical stimulation was used to neuromodulate a wide range of excitabilities of the lumbosacral spinal segments that would trigger rhythmic stepping movements. We observed that at the same intensity level of transcutaneous electrical spinal cord stimulation (tSCS), the presence or absence of visualizing a stepping-like movement of a stick figure immediately initiated or terminated the tSCS-induced rhythmic stepping motion, respectively. We also demonstrated that during both voluntary and imagined stepping, the motor potentials in leg muscles were facilitated when evoked cortically, using transcranial magnetic stimulation (TMS), and inhibited when evoked spinally, using tSCS. These data suggest that the ongoing assessment of the environment within the supraspinal centers that play a role in planning a movement can routinely modulate the physiological state of spinal networks that further facilitates a synergistic neuromodulation of the brain and spinal cord in preparing for movements.
Highlights
One factor that has been shown to be important, in movements such as locomotion, has been the degree of automaticity that is intrinsic to the neural networks that control stepping (Grillner, 2006; Rossignol and Frigon, 2011)
In our previous study we have shown that electromagnetic spinal cord stimulation or vibration of leg muscles were able to induce involuntary stepping movements ∼10% of tested healthy subjects placed in gravity neutral position (Gerasimenko et al, 2010)
When the subject was imagining performing the task as shown by the stick figure and visualized by the subject involuntary stepping movements were facilitated during Transcutaneous Electrical Spinal Cord Stimulation (tSCS) in all subjects (Supplementary Video 1)
Summary
One factor that has been shown to be important, in movements such as locomotion, has been the degree of automaticity that is intrinsic to the neural networks that control stepping (Grillner, 2006; Rossignol and Frigon, 2011). These networks have the ability to reorganize to rather dramatic functional levels when driven by activity-dependent mechanisms, which includes learning potential of spinal as well as supraspinal networks (Edgerton and Roy, 2009; Roy et al, 2012). In this study and in other similar studies, there has been little effort to understand how the spinal circuitry may be neuromodulated when imaginingvisualizing a motor task versus performing the motor task
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
