Engaging Cervical Spinal Cord Networks to Reenable Volitional Control of Hand Function in Tetraplegic Patients

Abstract

Background Paralysis of the upper-limbs from spinal cord injury results in an enormous loss of independence in an individual’s daily life. Meaningful improvement in hand function is rare after one year of tetraparesis. Therapeutic developments that result in even modest gains in hand volitional function will significantly impact the quality of life for patients afflicted with high cervical injury. The ability to neuromodulate the lumbosacral spinal circuitry via epidural stimulation in regaining postural function and volitional control of the legs has been recently shown. A key question is whether a similar neuromodulatory strategy can be used to improve volitional motor control of the upper-limbs, i.e., performance of motor tasks considered to be less “automatic” than posture and locomotion. In this study, the effects of cervical epidural stimulation on hand function are characterized in subjects with chronic cervical cord injury. Objective Herein we show that epidural stimulation can be applied to the chronic injured human cervical spinal cord to promote volitional hand function. Methods and results Two subjects implanted with an cervical epidural electrode array demonstrated improved hand strength (approximately three-fold) and volitional hand control in the presence of epidural stimulation. Conclusions The present data are sufficient to suggest that hand motor function in individuals with chronic tetraplegia can be improved with cervical cord neuromodulation and thus should be comprehensively explored as a possible clinical intervention.

Combination of Functional Electrical Stimulation and Noninvasive Spinal Cord Electrical Stimulation for Movement Rehabilitation of the Children with Cerebral Palsy

“…This effect is evident in spinal motor evoked potentials of proximal and distal leg muscles to single stimulation pulses [23]. We have found that epidural SCS combined with training can increase hand grip force in spinal patients with cervical injuries [18]. This suggests that similar interventions of training and cervical TSCS could also benefit for children with CP.…”

Trans-spinal direct current stimulation for the modulation of the lumbar spinal motor networks

“…Reported diameters for both axon types, including myelin, are within a range of 13 µm to 20 µm for afferent (Ia) fibers [46] and 16 µm to 20 µm for efferent axons originating from cortical Betz neurons [47,48]. The inner axonal diameter, without myelin, was estimated via multiplication of the g-ratio (g=0.6) [49], whereby the chosen axon diameter of 10 µm is within the resulting range for both axons.…”

“…For instance, whereas reducing spasticity may require the downregulation of the reflexive pathways, an increase in corticospinal connection strength is required when aiming to aid voluntary motor control. Further investigation in this direction could be performed by varying electric field amplitude and direction [10,11,49] in combination with pathway specific neural activity [10]. In parallel to that, screening for other, known genetic dependencies may additionally help to explain response differences across subjects [21].…”

“…Using both invasive [36,37,46,47] and noninvasive [38,48] approaches, as well as either sub- [38,46,48] and supra-threshold [38,47] pulsed stimulation, a variety of studies have reported significant long or short-term improvements on voluntary motor control, weight bearing or other clinical outcome parameters [36][37][38][46][47][48][49]. For instance, in a study by Gerasimenko and colleagues, several subjects diagnosed with motor complete paralysis were able to partly regain voluntary movement control after an 18-week training program, including weekly transcutaneous pulsed, supra-threshold spinal stimulation in combination with pharmaceutical intervention.…”

“…For instance, in a study by Gerasimenko and colleagues, several subjects diagnosed with motor complete paralysis were able to partly regain voluntary movement control after an 18-week training program, including weekly transcutaneous pulsed, supra-threshold spinal stimulation in combination with pharmaceutical intervention. Thus, while the more substantial improvements in voluntary control have only been achieved after long periods of combined manual training and electrical stimulation [36][37][38][46][47][48][49], immediate acute effects can already be observed during the first application [47,50].…”