How detailed is the central pattern generation for locomotion?

Spinal cord stimulation is a widespread treatment of chronic neuropathic pain from different conditions. Several novel and improving technologies have been recently developed to increase the effect of neuromodulation in patients refractory to pharmacological therapy.

To explore spinal cord stimulation’s mechanisms of action, indications, and management.

The paper initially explores the mechanism of action of this procedure based on the generation of an electric field between electrodes placed on the posterior dural surface of the spinal cord probably interfering with the transmission of pain stimuli to the brain. Subsequently, the most consolidated criteria for selecting patients for surgery, which constitute a major issue of debate, were defined. Thereafter, the fundamental patterns of stimulation were summarized by exploring the advantages and side effects. Lastly, the most common side effects and the related management were discussed.

Proper selection of the patient is of paramount importance to achieve the best results from this specific neuromodulation treatment. Regarding the different types of stimulation patterns, no definite evidence-based guidelines exist on the most appropriate approach in relation to the specific type of neuropathic pain. Both burst stimulation and high-frequency stimulation are innovative techniques that reduce the risk of paresthesias compared with conventional stimulation.

Novel protocols of stimulation (burst stimulation and high frequency stimulation) may improve the trade-off between therapeutic benefits and potential side effects. Likewise, decreasing the rates of hardware-related complications will be also useful to increase the application of neuromodulation in clinical settings.

This review is intended for clinicians, therapists and researchers interested in proprioception and its role in kinesthesia and the control of movement. First, the neurophysiological basis of proprioception is summarized, identifying the sensory receptors involved and how their signals mediate the perception and control of bodily movement. Past and present hypotheses and the continuing uncertainties and controversies that surround them are outlined. Psychophysical experiments that have helped identify the contribution of proprioceptive receptors to kinesthesia in humans are briefly reviewed. The article then discusses proprioceptive deficits, what causes them, how they are treated and how proprioceptive acuity is assessed.

Sensory information arising from limb movements controls the spinal locomotor circuitry to adapt the motor pattern to demands of the environment. Stimulation of extensor group (gr) I afferents during fictive locomotion in decerebrate cats prolongs the ongoing extension, and terminates ongoing flexion with an initiation of the subsequent extension, i. e. “resetting to extension”. Moreover, instead of the classical Ib non-reciprocal inhibition, stimulation of extensor gr I afferents produces a polysynaptic excitation in extensor motoneurons with latencies (∼3.5–4.0 ms) compatible with 3 interposed interneurons. We assume that some interneurons in this pathway actually belong to the rhythm-generating layer of the locomotor Central Pattern Generator (CPG), since their activity was correlated to a resetting of the rhythm. In the present work fictive locomotion was (mostly) induced by i.v. injection of nialamide followed by l-DOPA in paralyzed cats following decerebration and spinalization at C1 level. In some experiments, we extended previous observations during fictive locomotion on the emergence and locomotor state-dependence of polysynaptic excitatory postsynaptic potentials from extensor gr I afferents to ankle extensor motoneurons. However, the main focus was to record location and properties of interneurons (n = 62) that (i) were active during the extensor phase of fictive locomotion and (ii) received short-latency excitation (mono-, di- or polysynaptic) from extensor gr I afferents. We conclude that the interneurons recorded fulfill the characteristics to belong to the neuronal pathway activated by extensor gr I afferents during locomotion, and may contribute to the ‘resetting to extension’ as part of the locomotor CPG.

An animal at rest or engaged in stationary behaviors can instantaneously initiate goal-directed walking. How descending brain inputs trigger rapid transitions from a non-walking state to an appropriate walking state is unclear. Here, we identify two neuronal types, P9 and BPN, in the Drosophila brain that, upon activation, initiate and maintain two distinct coordinated walking patterns. P9 drives forward walking with ipsilateral turning, receives inputs from central courtship-promoting neurons and visual projection neurons, and is necessary for a male to pursue a female during courtship. In contrast, BPN drives straight, forward walking and is not required during courtship. BPN is instead recruited during and required for fast, straight, forward walking bouts. Thus, this study reveals separate brain pathways for object-directed walking and fast, straight, forward walking, providing insight into how the brain initiates context-appropriate walking programs.

The cat model has a rich tradition in our understanding of the neural control of locomotion. Arguably, the most important discoveries for the neural control of locomotion are the demonstrations that a spinal network generates the basic pattern of locomotion and that a region located within the midbrain initiates locomotion and participates in increasing stepping speed. Both these landmark discoveries were first shown in the cat model. In this chapter, I review the contribution of the cat model to the neural control of locomotion. I first start with a historical perspective followed by contributions made by the cat model to our understanding of the neural control of locomotion in three main areas: (1) control by spinal mechanisms, (2) control by somatosensory feedback, and (3) control by supraspinal structures.

Lampreys are basal vertebrates with a nervous system very similar to that of mammals but with a much smaller size and far fewer neurons. The lamprey nervous system can be entirely maintained in vitro for extended periods of time (easily up to 40 h). For these reasons, the lamprey has been considered as a model of choice to characterize the neural mechanisms underlying locomotion at the system, cellular, and subcellular levels since its introduction in the late 1970s by Sten Grillner and his collaborators in Sweden. This chapter summarizes some of the salient discoveries made in lampreys and examines how this animal model will likely be the source of future exciting discoveries on the neural control of locomotion.