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

Frontiers in Neurology, 2021 · DOI: 10.3389/fneur.2021.627975 · Published: May 10, 2021

Spinal Cord Injury Neurology Neurorehabilitation

Simple Explanation

This study investigates how combining brain and spinal cord stimulation with locomotor training affects neurophysiological changes in individuals with spinal cord injury (SCI). The rationale is that such combined interventions, despite being common in clinical practice, are not frequently studied in research. The research explores two protocols: TMS (transcranial magnetic stimulation) delivered before transspinal stimulation, and TMS delivered after transspinal stimulation. The study hypothesizes that the timing of these stimulations influences the reorganization of spinal networks during stepping. The study found that both stimulation protocols, when paired with locomotor training, promoted a more physiological modulation of motor activity, suggesting that targeting corticospinal and spinal pathways can benefit stepping in individuals with SCI.

Study Duration

Not specified

Participants

14 individuals with motor incomplete and complete SCI

Evidence Level

Randomized clinical trial

Key Findings

1
Transspinal-TMS PAS and locomotor training improved reﬂex inhibition during the swing phase when H-reﬂexes were grouped based on the TMS-targeted leg.
2
TMS-transspinal PAS and locomotor training improved excitation and stabilization of reﬂexively induced motoneuronal depolarization during the stance phase when H-reﬂexes were grouped based on the TMS-targeted leg.
3
Both transspinal-TMS and TMS-transspinal PAS and locomotor training increased EMG amplitude and promoted a more physiological modulation of motor activity.

Research Summary

The study investigated the effects of locomotor training coupled with paired transspinal and TMS on soleus H-reﬂex phase-dependent amplitude modulation in individuals with chronic motor incomplete and complete SCI. Transspinal-TMS PAS and locomotor training facilitated the left soleus H-reﬂex during mid-stance and early-swing, while depressing the right soleus H-reﬂex during mid-swing, and decreased the soleus H-reﬂex input-output curve in the right leg at rest. TMS-transspinal PAS and locomotor training did not produce signiﬁcant changes on the soleus H-reﬂex during stepping or at rest, suggesting the importance of stimulation timing in affecting spinal reflex reorganization.

Practical Implications

Targeted Intervention

Based on the SCI-induced pathological behavior of reﬂex modulation, transspinal-TMS or TMS-transspinal PAS may provide a targeted intervention.

Combined Therapies

The resemblance between the reﬂex reorganization observed in this study and locomotor training alone supports the use of combined interventions that target stimulation of the brain and spinal cord with exercise-based therapies.

Restoration of Muscle Control

Restoration of phase-dependent soleus H-reﬂex amplitude modulation and EMG amplitude during assisted stepping could potentially facilitate appropriate control of leg muscles during locomotion in this patient population.

Study Limitations

1
Neurophysiological tests were not performed at diﬀerent time points following cessation of the intervention, limiting the assessment of neuroplasticity sustainability.
2
The lack of control experiments, such as brain or transspinal stimulation alone or locomotor training without stimulation, makes it difficult to isolate the specific effects of the combined intervention.
3
The PAS protocol is uniquely diﬀerent from PAS protocols targeting the brain and peripheral nerves.

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