The nociceptive withdrawal reflex of the trunk is organized with unique muscle receptive fields and motor strategies

Abstract

Noxious stimuli induce a nociceptive withdrawal reflex (NWR) to protect the tissue from injury. Although the NWR was once considered as a stereotyped response, previous studies report distinct responses depending on the stimulation site and context for limbs. We aimed to determine whether noxious stimuli over the trunk produced adaptable complex NWR. We hypothesized that organization of the NWR of the trunk muscle would vary with the site of noxious input and would differ between body and spine postures, which modify the potential for specific muscles to remove threat. Fourteen participants were tested in sitting and three lumbar spine postures in side lying (neutral, flexion and extension). Noxious electrical stimuli were applied over the sacrum, spinous process of L3 and T12, lateral side of the 8th rib and anterior midline. NWR latency and amplitude were recorded with surface electromyography (EMG) electrodes over different trunk muscles. Distinct patterns of muscle activation depended on the stimulation site and were consistent with motor strategies needed to withdraw from the noxious stimuli. The NWR pattern differed between body positions, with less modulation observed in sitting than side lying. Spine posture did not affect the NWR organisation. Our results suggest the circuits controlling trunk muscle NWR presents with adaptability as a function of stimulation site and body position by utilizing the great complexity of the trunk muscle system to produce an efficient protective response. This suggests that the central nervous system (CNS) uses multiple adaptable strategies that are unique depending on which context the noxious stimuli are applied.

The effect of experimental pain on the excitability of the corticospinal tract in humans: A systematic review and meta‐analysis

“…Although our results are difficult to generalize to pain conditions, many studies reported changes in TMS outcomes in clinical populations (e.g. (Massé-Alarie et al, 2016;Salerno et al, 2000). This highlights the relevance to use TMS in experimental or clinical pain.…”

“…Some authors suggested that the role of the rapid reduction in corticospinal excitability consecutive to phasic pain is to foster the apparition of a spinal withdrawal reflex (Farina et al., 2003). Indeed, the withdrawal reflex represents a multisegmental functional movement tuned to noxious location (Andersen et al., 1999; Massé‐Alarie et al., 2019) partially controlled at the spinal cord. However, considering that noxious stimulus modulate EMG activity (e.g.…”

Motor Responses of Lumbar Erector Spinae Induced by Electrical Vestibular Stimulation in Seated Participants

“…The amplitude of the motor response was calculated as a percentage of the MVC after subtracting the pre-stimulus rms EMG (from –110 to –10 ms). This method allowed determining the direction of the response (excitatory vs. inhibitory) relative to the participant’s maximal contraction ( Massé-Alarie et al, 2019 ). The occurrence was calculated as the percentage of participants having a discernible inhibitory/excitatory motor response (on the average rectified EMG signal of the 15 stimuli) on the total number of participants tested.…”

Spinal spatial integration of nociception and its functional role assessed via the nociceptive withdrawal reflex and psychophysical measures in healthy humans

“…In this study, the use of double simultaneous stimulation with different IED enabled us to investigate the spinal nociceptive system in relation to spatial aspects of nociceptive integration and further interpreting the critical defensive role of the NWR in the perspective of the modular reflex organization (Andersen, 2007;Andersen et al, 1999;Julious, 2004;Levinsson et al, 1999;Massé-Alarie et al, 2019;Schouenborg et al, 1994;Sonnenborg et al, 2000).…”

“…The NWR pathway, however, has a different projection compared to the ascending fibers within the spinal cord (Eccles and Lundberg, 1959;Schomburg, 1990). The reflex arc integrates afferent inputs across a well-defined skin area to generate optimal withdrawal of the exposed area (Andersen, 2007;Kugelberg et al, 1960;Massé-Alarie et al, 2019;Schouenborg & Kalliomäki, 1990;Schouenborg et al, 1994). As a large amount of evidence has been collected supporting the hypothesis that spinal networks likely contribute to the observations of spatial summation and lateral inhibition (Andersen et al, 1994;Coghill et al, 1993aCoghill et al, , 1993bMørch et al, 2010;Price et al, 1989;Quevedo & Coghill, 2009;Quevedo et al, 2017;Wagman & Price, 1969), it would be highly interesting to apply a methodology to investigate these phenomena capable of assessing the spinal circuitry.…”