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Comparison of the effect of neuromodulation of the cervical or lumbar spinal cord on nociceptive processing in healthy volunteers

Knaepen, Clara

(2023)

Details

Supervisors

Mouraux, André ; Steyaert, Arnaud

Degree label

Master [120] en sciences biomédicales, à finalité approfondie

Abstract

In the past few years, studies have aimed at developing transcutaneous spinal direct current stimulation as a non-invasive tool to modulate motor and sensory spinal functions in humans. Regarding nociceptive processing, low-thoracic anodal tsDCS has been shown to modulate laser-evoked potentials, the perception of nociceptive mechanical stimuli, and temporal summation of pain. However, previous studies have failed to show an effect of tsDCS applied at the cervical level, possibly because the stimulation protocol was not optimal. In the present study, we aimed to compare the effects of low-thoracic and cervical anodal tsDCS (with an optimized montage) on nociceptive processing. We conducted a within-subjects, cross-over, double-blinded study, where twenty-four healthy volunteers participated in two experimental sessions. We assessed the brain responses and perception elicited by nociceptive contact heat stimuli, the intensity of perception to nociceptive mechanical stimuli, as well as the magnitude of temporal summation of pain, at baseline and after 20 minutes of either cervical or low-thoracic anodal tsDCS. Stimuli were delivered to the dominant forearm and foot dorsum. The amplitude of the CHEP-N2 wave remained similar before and after cervical and low-thoracic tsDCS for stimuli delivered to the forearm, however it decreased for stimuli delivered to the foot. Regarding our behavioral measures, CHEP NRS ratings were significantly higher for the forearm compared to the foot and significantly higher post-stimulation compared to baseline for the arm, but not for the foot. Lastly, our results for the NRS ratings to pinprick stimuli showed that, for the foot, ratings were lower post-stimulation compared to baseline following both cervical and low-thoracic tsDCS. The results of the present study do not support a differential effect of cervical and low-thoracic stimulation on behavioral and EEG responses to nociceptive stimuli. This absence of difference may be explained either by an absence of effect or by a similar effect of both stimulation protocols. While the absence of sham stimulation makes it impossible to definitively exclude that the observed findings are, in fact, the result of an absence of neuro-modulatory effects by both montages, we do believe our stimulation protocol was valid and correctly applied. Overall, our results are more consistent with some sort of supraspinal mechanism(s) which would have a differential effect on the upper and lower limb than with a segmental effect on the synaptic efficacy of the local processing and/or transmission of nociceptive inputs at the level of the dorsal horn.