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 (30 Hz, 0.6 g) 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.

Sustained submaximal contraction yields biphasic modulation of soleus Post‐activation depression in healthy humans

“…In pathologies such as spinal cord injury (SCI), changes in H‐reflex behavior signify reorganization of spinal circuitry and may be germane to clinical syndromes such as spasticity . The normalization of H‐reflex behavior to a pre‐SCI pattern is a potential target for post‐SCI rehabilitation interventions . Understanding the conditions that modulate H‐reflex excitability in neurologically intact humans is an important foundation for the development of therapies for patients with neurologic pathology.…”

“…2 The normalization of H-reflex behavior to a pre-SCI pattern is a potential target for post-SCI rehabilitation interventions. 3,4 Understanding the conditions that modulate H-reflex excitability in neurologically intact humans is an important foundation for the development of therapies for patients with neurologic pathology.…”

Limb Segment Load Inhibits the Recovery of Soleus H-Reflex After Segmental Vibration in Humans

“…After SCI, reorganization of spinal circuitry leads to loss of post activation depression (Ashby, Verrier, & Lightfoot, 1974; Calancie et al, 1993; Hiersemenzel, Curt, & Dietz, 2000; Schindler-Ivens & Shields, 2000; Shields, 2002; Skinner, Houle, Reese, Berry, & Garcia-Rill, 1996). We recently showed that constrained-limb vibration training can initiate a restoration of post-activation depression, even in patients with long-standing SCI (Yen, McHenry, Petrie, Dudley-Javoroski, & Shields, 2017). Vibration training may therefore have merit as an intervention to trigger neural adaptation in patients with SCI.…”

Activity-dependent synaptic dynamics in motor circuits of the spinal cord

“…In contrast, compressive loading of limb segments fails to modulate PAD in SCI patients, revealing a decreased capability of spinal segment below the lesion to respond to short episodes of sensory stimulation [25]. However, an ever-growing body of evidence suggests that the reactivation of sensorimotor pathways for example by passive cycling movements, treadmill training, physical therapy or robotic-assisted gait training improve functional motor recovery and restore PAD expression in both humans and animals after SCI or stroke [20,[26][27][28]. The changes in PAD rate observed after motor mobilization requires the integrity of the sensory afferent pathways [29] and are accompanied by improvement in balance control [20].…”

“…In this sense, TBS and STDP-like protocols appear to be highly valuable tools towards obtaining therapeutic benefits. In this context, it is noteworthy, that the data gathered on the PAD of H-reflex show that functional motor recovery is always associated with the restoration of a capability for synaptic plasticity (or vice versa) [20,[26][27][28]. Such findings lead to the chicken and egg dilemma.…”