Vibration training after chronic spinal cord injury: Evidence for persistent segmental plasticity

Abstract

H-reflex paired-pulse depression is gradually lost within the first year post-SCI, a process believed to reflect reorganization of segmental interneurons after the loss of normal descending (cortical) inhibition. This reorganization co-varies in time with the development of involuntary spasms and spasticity. The purpose of this study is to determine whether long-term vibration training may initiate the return of H-reflex paired-pulse depression in individuals with chronic, complete SCI. Five men with SCI received twice-weekly vibration training (30Hz, 0.6g) to one lower limb while seated in a wheelchair. The contra-lateral limb served as a within-subject control. Paired-pulse H-reflexes were obtained before, during, and after a session of vibration. Untrained limb H-reflex depression values were comparable to chronic SCI values from previous reports. In contrast, the trained limbs of all 5 participants showed depression values that were within the range of previously-reported Acute SCI and Non-SCI H-reflex depression. The average difference between limbs was 34.98% (p=0.016). This evidence for the return of H-reflex depression suggests that even for people with long-standing SCI, plasticity persists in segmental reflex pathways. The spinal networks involved with the clinical manifestation of spasticity may thus retain adaptive plasticity after long-term SCI. The results of this study indicate that vibration training may hold promise as an anti-spasticity rehabilitation intervention.

Keywords: H-reflex; Paralysis; Post-activation depression; Pre-synaptic inhibition; Spasticity.

Copyright © 2017 Elsevier B.V. All rights reserved.

Figures

Figure 1

Schematic representation of the constrained-limb vibration system.

Figure 2

Mean (SE) H1 and H2 normalized to HB Before (leftmost bars), During (grey region) and After vibration (rightmost bars) for the trained and untrained limbs. * = significantly different from Before and After, p

Figure 3

A) Mean (SE) Depression ratio (100* (HB-H2)/HB) for the Before, During and After conditions for the trained and untrained limbs. * = significantly different from Before and After, both p