Spinal automaticity of movement control and its role in recovering function after spinal injury

INTRODUCTION

The significance of the spinal circuitry in controlling postural and locomotor functions largely re-emerged in the mid-1970s under the leadership of Sten Grillner, demonstrating key phenomena of "central pattern generation" and "fictive locomotion" with an evolutionary perspective. These concepts raised the question of how much function can be recovered after paralysis, given the intrinsic automaticity of spinal networks in injured and uninjured states in adults.

AREAS COVERED

This review explores biological mechanisms governing spinal control of movements such as posture and locomotion. We focus on concepts that have evolved from experiments performed over the past decade. Rather than a comprehensive review of the vast literature on the neural control of posture and locomotion, we focus on the various mechanisms underlying functional automaticity, and their clinical relevance.

EXPERT OPINION

We propose that multiple combinations of sensory mechanoreceptors linked to proprioception generate an infinite number of different sensory ensembles, having species-specific meaning and extensive influence in controlling posture and locomotion. These sensory ensembles are translated as a probabilistic phenomenon into highly specific but indeterminate actions. Therefore, we opine that spinal translation of these ensembles in real-time plays a central role in the automaticity of motor control in individuals with and without severe neuromotor dysfunction.

Isolating Transcutaneous Spinal Cord Stimulation Artifact to Identify Motor Response during Walking

The objective of this investigation was to demonstrate the applicability of a custom-developed EMD-Notch filtering algorithm to isolate the scTS-induced artifact from sEMG signals during walking in an individual with motor-incomplete SCI. Overall, the EMD-Notch filtering algorithm provides an effective approach to isolate the scTS artifact, extract the sEMG data, and further study the modulation of the spinal neuronal networks during dynamic activities.Clinical Relevance- This investigation will help with the modification of individualized scTS parameters to achieve task-specific neuromodulatory effects.

Neurorestorative interventions involving bioelectronic implants after spinal cord injury

In the absence of approved treatments to repair damage to the central nervous system, the role of neurosurgeons after spinal cord injury (SCI) often remains confined to spinal cord decompression and vertebral fracture stabilization. However, recent advances in bioelectronic medicine are changing this landscape. Multiple neuromodulation therapies that target circuits located in the brain, midbrain, or spinal cord have been able to improve motor and autonomic functions. The spectrum of implantable brain-computer interface technologies is also expanding at a fast pace, and all these neurotechnologies are being progressively embedded within rehabilitation programs in order to augment plasticity of spared circuits and residual projections with training. Here, we summarize the impending arrival of bioelectronic medicine in the field of SCI. We also discuss the new role of functional neurosurgeons in neurorestorative interventional medicine, a new discipline at the intersection of neurosurgery, neuro-engineering, and neurorehabilitation.

Spinal cord repair: advances in biology and technology

Individuals with spinal cord injury (SCI) can face decades with permanent disabilities. Advances in clinical management have decreased morbidity and improved outcomes, but no randomized clinical trial has demonstrated the efficacy of a repair strategy for improving recovery from SCI. Here, we summarize recent advances in biological and engineering strategies to augment neuroplasticity and/or functional recovery in animal models of SCI that are pushing toward clinical translation.

Epidural and transcutaneous spinal electrical stimulation for restoration of movement after incomplete and complete spinal cord injury

PURPOSE OF REVIEW

The Purpose of this review is to outline and explain the therapeutic use of electrical spinal cord stimulation (SCS) for modification of spinal motor output. Central functional stimulation provides afferent input to posterior root neurons and is applied to improve volitional movements, posture and their endurance, control spasticity, and improve bladder function or perfusion in the lower limbs. Clinical accomplishments strongly depend on each individual's physiological state and specific methodical adaptation to that physiological state.

RECENT FINDINGS

Effectiveness of this neuromodulory technique for changing motor control after spinal cord injury (SCI) continues to be explored along with the underlying mechanisms of its effect in people with complete and incomplete spinal cord injuries. There are extensive studies of tonic and rhythmical activity elicited from the lumbar cord as well as data demonstrating augmentation of residual volitional activity. Recent studies have focused on verifying if and how SCS can modify features of neurocontrol in ambulatory spinal cord patients.

SUMMARY

In this review, we emphasize recent publications of research revealing that SCS can substitute for the reduced brain drive for control of excitability in people with SCI. Artificially replacing diminished or lost brain control over the spinal cord has limitations. A fundamental requirement for successful SCS application is analysis of each individual's residual postinjury neural function. This will allow a better understanding of the physiological interactions between SCS and spinal cord motor control below injury and provide criteria for its application. Finally, the publication of both successful and failed applications of SCS will be crucial for gaining future progress.