Does Trans-Spinal Direct Current Stimulation Alter Phrenic Motoneurons and Respiratory Neuromechanical Outputs in Humans? A Double-Blind, Sham-Controlled, Randomized, Crossover Study

Abstract

Although compelling evidence has demonstrated considerable neuroplasticity in the respiratory control system, few studies have explored the possibility of altering descending projections to phrenic motoneurons (PMNs) using noninvasive stimulation protocols. The present study was designed to investigate the immediate and long-lasting effects of a single session of transcutaneous spinal direct current stimulation (tsDCS), a promising technique for modulating spinal cord functions, on descending ventilatory commands in healthy humans. Using a double-blind, controlled, randomized, crossover approach, we examined the effects of anodal, cathodal, and sham tsDCS delivered to the C3-C5 level on (1) diaphragm motor-evoked potentials (DiMEPs) elicited by transcranial magnetic stimulation and (2) spontaneous ventilation, as measured by respiratory inductance plethysmography. Both anodal and cathodal tsDCS induced a progressive increase in DiMEP amplitude during stimulation that persisted for at least 15 min after current offset. Interestingly, cathodal, but not anodal, tsDCS induced a persistent increase in tidal volume. In addition, (1) short-interval intracortical inhibition, (2) nonlinear complexity of the tidal volume signal (related to medullary ventilatory command), (3) autonomic function, and (4) compound muscle action potentials evoked by cervical magnetic stimulation were unaffected by tsDCS. This suggests that tsDCS-induced aftereffects did not occur at brainstem or cortical levels and were likely not attributable to direct polarization of cranial nerves or ventral roots. Instead, we argue that tsDCS could induce sustained changes in PMN output. Increased tidal volume after cathodal tsDCS opens up the perspective of harnessing respiratory neuroplasticity as a therapeutic tool for the management of several respiratory disorders.

Motor cortex and spinal cord neuromodulation promote corticospinal tract axonal outgrowth and motor recovery after cervical contusion spinal cord injury

“…iTBS is routinely performed non-invasively using TMS (Huang et al, 2005). tsDCS is non-invasive and has been performed safely in human cervical spinal cord for modulating respiratory function (Niérat et al, 2014). A potential advantage of the “open loop” neuromodulatory approach used in this study is that it does not depend on the timing of critical neural events, such as with paired associative stimulation (Thickbroom, 2007), or on the occurrence of motor event, such as in “closed loop” stimulation paradigms (e.g., (McPherson et al, 2015)).…”

Concurrent electrical cervicomedullary stimulation and cervical transcutaneous spinal direct current stimulation result in a stimulus interaction

“…Another study that did examine motor responses during cervical tsDCS showed an increase in diaphragm MEPs (Niérat et al . ). Thus, we tested both MEPs and CMEPs in the upper limb during the application of cervical tsDCS.…”

“…C, averaged eCMEPs and mCMEPs (10-15 traces) for a single participant (upper traces are eCMEPs, and examine these potentials during stimulation (Dongés et al 2017). Another study that did examine motor responses during cervical tsDCS showed an increase in diaphragm MEPs (Niérat et al 2014). Thus, we tested both MEPs and CMEPs in the upper limb during the application of cervical tsDCS.…”

“…The diaphragm muscle responses were also modified during periods of tsDCS (Niérat et al . ). Both of these studies reported an increase in the size of muscle responses regardless of the polarity of tsDCS electrodes used.…”

“…The delivery of cervical tsDCS using an anterior-posterior electrode configuration has been reported to increase upper limb and diaphragm muscle responses to transcranial magnetic stimulation (TMS) of the motor cortex after tsDCS (Lim & Shin, 2011;Niérat et al 2014). The diaphragm muscle responses were also modified during periods of tsDCS (Niérat et al 2014). Both of these studies reported an increase in the size of muscle responses regardless of the polarity of tsDCS electrodes used.…”