H‐reflex conditioning during locomotion in people with spinal cord injury

Abstract

r In people or animals with incomplete spinal cord injury (SCI), changing a spinal reflex through an operant conditioning protocol can improve locomotion.r All previous studies conditioned the reflex during steady-state maintenance of a specific posture. By contrast, the present study down-conditioned the reflex during the swing-phase of locomotion in people with hyperreflexia as a result of chronic incomplete SCI. The aim was to modify the functioning of the reflex in a specific phase of a dynamic movement.r This novel swing-phase conditioning protocol decreased the reflex much faster and farther than did the steady-state protocol in people or animals with or without SCI, and it also improved locomotion.r The reflex decrease persisted for at least 6 months after conditioning ended. r The results suggest that conditioning reflex function in a specific phase of a dynamic movement offers a new approach to enhancing and/or accelerating recovery after SCI or in other disorders.Abstract In animals and people with incomplete spinal cord injury, appropriate operant conditioning of a spinal reflex can improve impaired locomotion. In all previous conditioning studies, the reflex was conditioned during steady-state maintenance of a stable posture; this steady-state protocol aimed to change the excitability of the targeted reflex pathway; reflex size gradually changed over 8-10 weeks. The present study introduces a new protocol, comprising a dynamic protocol that aims to change the functioning of the reflex pathway during a specific phase of a complex movement. Specifically, we down-conditioned the soleus H-reflex during the swing-phase of locomotion in people with hyperreflexia as a result of chronic incomplete SCI. The swing-phase H-reflex, which is absent or very small in neurologically normal individuals, is abnormally large in this patient population. The results were clear. With swing-phase down-conditioning, the H-reflex decreased much faster and farther than did the H-reflex in all previous animal or human studies with the steady-state protocol, and the decrease persisted for at least 6 months after conditioning ended. The H-reflex decrease was accompanied by Aiko Thompson received her PhD in Neuroscience from the University of Alberta, Canada, and carried out postdoctoral training at the Wadsworth Center in Albany, NY, USA. She developed the original human H-reflex operant conditioning protocol and conducted the first H-reflex conditioning study in people with spinal cord injury, in which successful reflex conditioning improved people's walking. The research goals of her laboratory are to understand the human CNS plasticity related to motor control and to learn how to guide such plasticity to help restore useful movement function in people after injuries to the nervous system. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commerc...

Neurophysiological Changes After Paired Brain and Spinal Cord Stimulation Coupled With Locomotor Training in Human Spinal Cord Injury

“…In neurologically intact individuals, soleus H-reflex amplitudes are minimal during swing and at heel contact, increase rapidly during stance, and decrease abruptly after toe-off (42,46). SCI disrupts this phase-dependent soleus H-reflex amplitude modulation during walking, varying from relatively normal in some patients to completely absent in others (7,8,12,39,47). The most common change observed after locomotor training is the partial return of soleus H-reflex depression during the swing phase; but extensor motoneuron excitability during the stance phase remains unstable (12,39).…”

Lost in Translation: Simple Steps in Experimental Design of Neurorehabilitation-Based Research Interventions to Promote Motor Recovery Post-Stroke

“…Note that a simple contextualization can drive motivation if the participant sees how the task can positively impact their life outside of the research lab, yet these person-centered outcomes are rarely if ever included in research protocols (Winstein, 2018). To further support our argument, recent studies have shown that motivation can mediate long-lasting neural plasticity: for example, operant conditioning protocols use a reward-based approach to downregulate plantarflexor muscle H-reflex through brain and spinal cord plasticity (Wolpaw et al, 1986;Thompson and Wolpaw, 2014;Chen et al, 2017), which can restore preinjury reflex excitability and invoke positive changes in walking function (Thompson et al, 2013;Thompson and Wolpaw, 2019). Therefore, the contextualization process establishes meaningful goals linked to the research task being used to promote recovery through fundamental learning-based processes, supported by brain and spinal cord plasticity (Tsay and Winstein, 2020).…”

Can Operant Conditioning of EMG-Evoked Responses Help to Target Corticospinal Plasticity for Improving Motor Function in People With Multiple Sclerosis?

“…Among the major descending pathways, the corticospinal tract is the only pathway essential for conditioning-induced plasticity ( 97 ). Thus, when the corticospinal tract and its plasticity are preserved at least partially, the targeted change can be induced through conditioning ( 98 ), which then changes how that reflex pathway functions in complex motion such as locomotion ( 80 , 92 , 99 ). These provide the foundation for currently emerging clinical applications of MEP operant conditioning.…”

“…In addition to MEP conditioning protocols, several reflex conditioning protocols are currently being developed. To date, two protocols have been systematically tested in people with or without CNS damage: the soleus short-latency stretch reflex (known as M1 response) conditioning, using mechanical joint perturbation ( 135 ), and the soleus H-reflex conditioning, which uses electrical stimulation of the tibial nerve ( 92 , 99 , 102 , 136 ). With both stretch and H-reflex conditioning protocols, the person learns to increase or decrease the target reflex size over 24–30 conditioning sessions.…”

“…Up until now, the majority of evoked potential operant conditioning studies have been done in SCI ( 68 , 80 , 82 , 92 , 99 , 141 – 145 ), and its investigation in MS is still in an early stage. Unique challenges in the MS population that do not necessarily apply to the SCI population include impaired cognitive function, fatigue, and ongoing and/or recurring inflammation ( 14 , 56 , 59 , 146 ).…”