A neural circuitry that emphasizes spinal feedback generates diverse behaviours of human locomotion

Abstract

Key pointsr It is often assumed that central pattern generators, which generate rhythmic patterns without rhythmic inputs, play a key role in the spinal control of human locomotion.r We propose a neural control model in which the spinal control generates muscle stimulations mainly through integrated reflex pathways with no central pattern generator.r Using a physics-based neuromuscular human model, we show that this control network is sufficient to compose steady and transitional 3-D locomotion behaviours, including walking and running, acceleration and deceleration, slope and stair negotiation, turning, and deliberate obstacle avoidance.r The results suggest feedback integration to be functionally more important than central pattern generation in human locomotion across behaviours.r In addition, the proposed control architecture may serve as a guide in the search for the neurophysiological origin and circuitry of spinal control in humans.Abstract Neural networks along the spinal cord contribute substantially to generating locomotion behaviours in humans and other legged animals. However, the neural circuitry involved in this spinal control remains unclear. We here propose a specific circuitry that emphasizes feedback integration over central pattern generation. The circuitry is based on neurophysiologically plausible muscle-reflex pathways that are organized in 10 spinal modules realizing limb functions essential to legged systems in stance and swing. These modules are combined with a supraspinal control layer that adjusts the desired foot placements and selects the leg that is to transition into swing control during double support. Using physics-based simulation, we test the proposed circuitry in a neuromuscular human model that includes neural transmission delays, musculotendon dynamics and compliant foot-ground contacts. We find that the control network is sufficient to compose steady and transitional 3-D locomotion behaviours including walking and running, acceleration and deceleration, slope and stair negotiation, turning, and deliberate obstacle avoidance. The results suggest feedback integration to be functionally more important than central pattern generation in human locomotion across behaviours. In addition, the proposed control architecture may serve as a guide in the search for the neurophysiological origin and circuitry of spinal control in humans.

A Robust Parameterization of Human Gait Patterns Across Phase-Shifting Perturbations

“…Biomechanical signals involved in key reflex pathways [25] may be closely related to the phase of human gait. In particular, the neuro-science literature suggests that muscle afferents acting at the hip joint are essential to controlling the more distal joints of the leg (e.g., knee and ankle) in mammalian locomotion [26].…”

A Perturbation Mechanism for Investigations of Phase-Dependent Behavior in Human Locomotion

“…As previously mentioned in the introduction, there are multiple hypotheses about the neuromechanics involved during locomotion. Due to the simplicity of the perturbation used in these experiments, scientists could simulate a perturbation of the same magnitude and response time as the one presented here and apply it to their models, e.g., [12] and [17]. One could compare the response of their models with respect to the actual human response, and thus help evaluate and improve their models.…”

“…Some hypotheses have proposed that there exists an internal clock, such as a central pattern generator (CPG) [12]–[14] or coupled oscillators [15], [16], helping keep the body synchronized and in rhythm through the entire gait cycle. However, other hypotheses propose that synchronization during walking could be achieved merely by reflex responses and that only synergistic cooperation between proprioception feedback and muscle activation is necessary to achieve stable locomotion [17]. These models inform neuroscientists about the different neural architectures that might be used in humans during locomotion.…”

“…These models inform neuroscientists about the different neural architectures that might be used in humans during locomotion. These models have been extensively studied in computer simulations [17], [18], but it would be of great interest to the scientific community to use human data to validate their accuracy.…”

Decentralized feedback controllers for exponential stabilization of hybrid periodic orbits: Application to robotic walking

“…However, human locomotion may employ a decentralized control scheme relying heavily on local feedback loops [12], [13]. Centralized control schemes designed for bipedal robots also cannot be easily transferred to powered prosthetic legs, which act as decentralized subsystems.…”