Spinal Interneurons: Diversity and Connectivity in Motor Control

The spinal cord is home to the intrinsic networks for locomotion. An animal in which the spinal cord has been fully severed from the brain can still produce rhythmic, patterned locomotor movements as long as some excitatory drive is provided, such as physical, pharmacological, or electrical stimuli. Yet it remains a challenge to define the underlying circuitry that produces these movements because the spinal cord contains a wide variety of neuron classes whose patterns of interconnectivity are still poorly understood. Computational models of locomotion accordingly rely on untested assumptions about spinal neuron network element identity and connectivity. In this review, we consider the classes of spinal neurons, their interconnectivity, and the significance of their circuit connections along the long axis of the spinal cord. We suggest several lines of analysis to move toward a definitive understanding of the spinal network.

Automated summary

The spinal cord is the location of intrinsic networks for locomotion. Even when the brain is fully severed from the spinal cord, as long as some excitatory drive is provided, animals can still produce rhythmic, patterned movements. However, the underlying circuitry that produces these movements remains poorly understood due to the wide variety of neuron classes and their interconnectivity in the spinal cord. This review considers the classes of spinal neurons, their interconnectivity, and suggests several lines of analysis to improve our understanding of the spinal network.