Mapping of the Spinal Sensorimotor Network by Transvertebral and Transcutaneous Spinal Cord Stimulation

Abstract

Transcutaneous stimulation is a neuromodulation method that is efficiently used for recovery after spinal cord injury and other disorders that are accompanied by motor and sensory deficits. Multiple aspects of transcutaneous stimulation optimization still require testing in animal experiments including the use of pharmacological agents, spinal lesions, cell recording, etc. This need initially motivated us to develop a new approach of transvertebral spinal cord stimulation (SCS) and to test its feasibility in acute and chronic experiments on rats. The aims of the current work were to study the selectivity of muscle activation over the lower thoracic and lumbosacral spinal cord when the stimulating electrode was located intravertebrally and to compare its effectiveness to that of the clinically used transcutaneous stimulation. In decerebrated rats, electromyographic activity was recorded in the muscles of the back (m. longissimus dorsi), tail (m. abductor caudae dorsalis), and hindlimb (mm. iliacus, adductor magnus, vastus lateralis, semitendinosus, tibialis anterior, gastrocnemius medialis, soleus, and flexor hallucis longus) during SCS with an electrode placed alternately in one of the spinous processes of the VT12–VS1 vertebrae. The recruitment curves for motor and sensory components of the evoked potentials (separated from each other by means of double-pulse stimulation) were plotted for each muscle; their slopes characterized the effectiveness of the muscle activation. The electrophysiological mapping demonstrated that transvertebral SCS has specific effects to the rostrocaudally distributed sensorimotor network of the lower thoracic and lumbosacral cord, mainly by stimulation of the roots that carry the sensory and motor spinal pathways. These effects were compared in the same animals when mapping was performed by transcutaneous stimulation, and similar distribution of muscle activity and underlying neuroanatomical mechanisms were found. The experiments on chronic rats validated the feasibility of the proposed stimulation approach of transvertebral SCS for further studies.

When Spinal Neuromodulation Meets Sensorimotor Rehabilitation: Lessons Learned From Animal Models to Regain Manual Dexterity After a Spinal Cord Injury

“…However, transcutaneous stimulation is scarcely studied in animals. Unstable fixation of the adhesive electrode on the animal's skin and the difficulty placing the electrodes identically during longitudinal studies limit its implementation and have led to the development of transvertebral electrical stimulation, in which electrodes are implanted into the vertebral spinous processes, with a mode of action and muscle responses analogous to those evoked by transcutaneous stimulation ( 153 ).…”

Trans-Spinal Electrical Stimulation Therapy for Functional Rehabilitation after Spinal Cord Injury: Review

“…To harness the benefits and to avoid the complications of an epidural SCS, a noninvasive spinal cord neuromodulation modality, called transcutaneous SCS, has been developed and investigated recently [ 45 , 46 , 47 , 48 ]. Transcutaneous stimulation can be induced alone or in combination with functional therapy, which leads to an increased motor function in patients with chronic paralysis [ 17 , 49 ].…”