Peeling back the layers of locomotor control in the spinal cord

Abstract

Vertebrate locomotion is executed by networks of neurons within the spinal cord. Here, we describe recent advances in our understanding of spinal locomotor control provided by work using optical and genetic approaches in mice and zebrafish. In particular, we highlight common observations that demonstrate simplification of limb and axial motor pool coordination by spinal network modularity, differences in the deployment of spinal modules at increasing speeds of locomotion, and functional hierarchies in the regulation of locomotor rhythm and pattern. We also discuss the promise of intersectional genetic strategies for better resolution of network components and connectivity, which should help us continue to close the gap between theory and function.

Decoding the organization of spinal circuits that control locomotion

“…There are four morphological classes of V0 V neurons, one of which is the multipolar commissural descending (MCoD) neurons that seem to be involved in rhythm generation rather than in left–right alternation (see below). Decisive information about the role of the other classes of inhibitory and excitatory V0 neurons for left–right coordination has not yet been obtained in zebrafish larvae 30,63,64 .…”

“…Part c is based on data from REFS 50,83,87,92. Part d is based on data from REFS 30,63,64,98,99. Part e is based on data from REFS 25,102.…”

“…In this way, it has been possible to probe these large-scale networks and reveal both molecular and physiological aspects of network organization in a behavioural context and to link neuronal populations to specific aspects of the behaviour. A similar approach has been instigated in the genetically tractable zebrafish 20,25,27,29,30,38 .…”

Investigation of the Intra- and Inter-Limb Muscle Coordination of Hands-and-Knees Crawling in Human Adults by Means of Muscle Synergy Analysis

“…Although many models have been proposed and discussed, people still do not know exactly how rhythmic motions are generated and controlled. The potential advantages, disadvantages, and the plausibility of the UBG and two-level structure were debated widely in related studies [41][42][43]. Taking advantage of its great potential in revealing the motor control strategy of the CNS, muscle synergy analysis was adopted to explore the intra-and inter-limb muscle coordination of human hands-and-knees crawling under different speeds in this study, and the results can help to understand the underlying neuromuscular control mechanism of CNS on crawling movement.…”

Modular organization of the multipartite central pattern generator for turtle rostral scratch: knee-related interneurons during deletions

“…More recently, investigators have gathered data in support of hypotheses suggesting more complex multipartite modular organization of spinal CPGs (Ampatzis et al 2014;Bagnall and McLean 2014;Bellardita and Kiehn 2015;Bizzi et al 2008;Duysens et al 2013;Giszter 2015;Giszter and Hart 2013;Grillner 1981;Grillner et al 2008b;Grillner and El Manira 2015;Hagglund et al 2013;Hao et al 2014;Hinckley et al 2015;Krouchev et al 2006;Krouchev and Drew 2013;Lacquaniti et al 2012;Markin et al 2012;McCrea and Rybak 2008;McLean and Dougherty 2015;Prilutsky and Edwards 2016;Stein 1985Stein , 2008Zhang et al 2014). Many of these studies conclude that the classic bipartite flexor/extensor halfcenter hypothesis is not sufficient to account for the specifics of spinal cord motor output and that a multipartite modular hypothesis is needed to account for important features of the experimental data.…”