Inhibition and Facilitation of the Spinal Locomotor Central Pattern Generator and Reflex Circuits by Somatosensory Feedback From the Lumbar and Perineal Regions After Spinal Cord Injury

Abstract

Somatosensory feedback from peripheral receptors dynamically interacts with networks located in the spinal cord and brain to control mammalian locomotion. Although somatosensory feedback from the limbs plays a major role in regulating locomotor output, those from other regions, such as lumbar and perineal areas also shape locomotor activity. In mammals with a complete spinal cord injury, inputs from the lumbar region powerfully inhibit hindlimb locomotion, while those from the perineal region facilitate it. Our recent work in cats with a complete spinal cord injury shows that they also have opposite effects on cutaneous reflexes from the foot. Lumbar inputs increase the gain of reflexes while those from the perineal region decrease it. The purpose of this review is to discuss how somatosensory feedback from the lumbar and perineal regions modulate the spinal locomotor central pattern generator and reflex circuits after spinal cord injury and the possible mechanisms involved. We also discuss how spinal cord injury can lead to a loss of functional specificity through the abnormal activation of functions by somatosensory feedback, such as the concurrent activation of locomotion and micturition. Lastly, we discuss the potential functions of somatosensory feedback from the lumbar and perineal regions and their potential for promoting motor recovery after spinal cord injury.

Spinal sensorimotor circuits play a prominent role in hindlimb locomotor recovery after staggered thoracic lateral hemisections but cannot restore posture and interlimb coordination during quadrupedal locomotion in adult cats

“…Although all cats recovered quadrupedal locomotion after staggered hemisections, some cats required perineal stimulation after the second hemisection ( Table 1 ), which increases spinal neuronal excitability and facilitates hindlimb locomotion in spinal mammals through an undefined mechanism (Eidelberg et al, 1980; Alluin et al, 2015; Harnie et al, 2019; Merlet et al, 2021; Audet et al, 2022). Previous studies proposed that the amount of locomotor training constitutes an important factor in locomotor recovery after partial spinal lesions (Kloos et al, 2005; Rossignol et al, 2009).…”

“…As described, the strength of perineal stimulation is difficult to quantify but we adjusted the pressure applied to the perineal region on a case-by-case basis (light/strong, tonic/rhythmic) to achieve the best hindlimb locomotor pattern possible (Caron et al, 2020; Audet et al, 2022). Perineal stimulation increases spinal excitability and facilitates hindlimb locomotion in spinal mammals through an undefined mechanism(Merlet et al, 2021). However, if the perineal stimulation was too strong, we observed exaggerated flexion of the hindlimbs (hip, knee and ankle) and/or improper left-right alternation, which impaired treadmill locomotion.…”

Novel Noninvasive Spinal Neuromodulation Strategy Facilitates Recovery of Stepping after Motor Complete Paraplegia

“…Other studies have also shown that scTS of the cervical area can lead to the facilitation of voluntary behaviors [28,31]. Lastly, stimulation of the sacral afferents has been shown to be an effective neuromodulator of the lower limb muscles [32,33]. We attempted to replicate this effect through scTS at the sacral-coccygeal level.…”

How Does the Central Nervous System for Posture and Locomotion Cope With Damage-Induced Neural Asymmetry?

“…Spinal cord injured animals are common models for studying neural plasticity ( Dietz and Fouad, 2014 ; Alizadeh et al, 2019 ) in the context of motor functions (respiration: Streeter et al, 2020 ; posture and locomotion: Brown and Martinez, 2019 ). Most species are capable of partial or complete recovery after SCI, demonstrating the intrinsic ability of spinal sensory-motor networks to organize functionally relevant motor commands even in the absence of part or all descending commands and neuromodulation ( Rossignol et al, 1996 ; but see also Merlet et al, 2021 ). Lumbar SCIs are more deleterious than mid-thoracic ones as reported in cats ( Rossignol et al, 2002 ) and rats ( García-Alías et al, 2006 ), probably because they may directly injure the locomotor CPG.…”