And yet it moves: Recovery of volitional control after spinal cord injury

• Published in: Progress in neurobiology Vol. 160; pp. 64 - 81
• Main Authors: Taccola, G, Sayenko, D, Gad, P, Gerasimenko, Y, Edgerton, V R
• Format: Journal Article
• Language: English
• Published: England Pergamon Press 01.01.2018
• Subjects: Animals; Humans; Motor Activity - physiology; Recovery of Function - physiology; Spinal Cord Injuries - physiopathology; Spinal Cord Injuries - therapy; Volition - physiology; Electrical stimulation; Spinal networks; Motor training; Neuromodulation
• ISSN: 0301-0082; 1873-5118
• DOI: 10.1016/j.pneurobio.2017.10.004

Preclinical and clinical neurophysiological and neurorehabilitation research has generated rather surprising levels of recovery of volitional sensory-motor function in persons with chronic motor paralysis following a spinal cord injury. The key factor in this recovery is largely activity-dependent plasticity of spinal and supraspinal networks. This key factor can be triggered by neuromodulation of these networks with electrical and pharmacological interventions. This review addresses some of the systems-level physiological mechanisms that might explain the effects of electrical modulation and how repetitive training facilitates the recovery of volitional motor control. In particular, we substantiate the hypotheses that: (1) in the majority of spinal lesions, a critical number and type of neurons in the region of the injury survive, but cannot conduct action potentials, and thus are electrically non-responsive; (2) these neuronal networks within the lesioned area can be neuromodulated to a transformed state of electrical competency; (3) these two factors enable the potential for extensive activity-dependent reorganization of neuronal networks in the spinal cord and brain, and (4) propriospinal networks play a critical role in driving this activity-dependent reorganization after injury. Real-time proprioceptive input to spinal networks provides the template for reorganization of spinal networks that play a leading role in the level of coordination of motor pools required to perform a given functional task. Repetitive exposure of multi-segmental sensory-motor networks to the dynamics of task-specific sensory input as occurs with repetitive training can functionally reshape spinal and supraspinal connectivity thus re-enabling one to perform complex motor tasks, even years post injury.