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.
Highlights
Terrestrial locomotion in mammals is a complex movement that engages all levels of the nervous system
We showed that mechanically stimulating the lumbar region with vibration or pinch increased ipsilateral and crossed shortlatency excitatory cutaneous reflex responses while perineal stimulation, in contrast, decreased reflex responses
We propose that somatosensory feedback from lumbar or perineal regions, the spinal locomotor central pattern generator (CPG) and/or the spinal circuitry for micturition project to a mechanism that controls neurotransmitter release of primary afferents and the excitability of neurons within the reflex pathways, thereby increasing or decreasing reflex gain
Summary
Terrestrial locomotion in mammals is a complex movement that engages all levels of the nervous system. Because of the spinal locomotor CPG and its interactions with somatosensory inputs, various sensorimotor functions recover, such as spinal reflexes and locomotion, in various mammals, such as mice, rats and cats, and even humans but to a lesser degree (Rossignol and Frigon, 2011). Somatosensory feedback from the limbs shapes the output of the spinal locomotor CPG, inputs from other body regions generate powerful inhibition or facilitation of locomotion. 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, the possible mechanisms involved and their potential functions.
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