Jean-Marie Cabelguen

Fractional Multi-models of the Frog Gastrocnemius Muscle

In this article, frog gastrocnemius muscles are studied, and a multi-model identification presented. A transfer function is defined with few parameters to simulate striated muscle (Gastroctnemius) behaviour, for inclusion in a future real-time salamander computer model. A two-model structure permits description of both contraction and relaxation properties. Here, two physiological influences, fatigue and fibre types, are taken into account. A multi-model structure for each fibre type (fast (IIB), intermediate (IIA) and slow (I) fibres) is also used for inclusion in a future agonist-antagonist structure computer model.

A Salamander’s Flexible Spinal Network for Locomotion, Modeled at Two Levels of Abstraction

Animals have to coordinate a large number of muscles in different ways to efficiently move at various speeds and in different and complex environments. This coordination is in large part based on central pattern generators (CPGs). These neural networks are capable of producing complex rhythmic patterns when activated and modulated by relatively simple control signals. Although the generation of particular gaits by CPGs has been successfully modeled at many levels of abstraction, the principles underlying the generation and selection of a diversity of patterns of coordination in a single neural network are still not well understood. The present work specifically addresses the flexibility of the spinal locomotor networks in salamanders. We compare an abstract oscillator model and a CPG network composed of integrate-and-fire neurons, according to their ability to account for different axial patterns of coordination, and in particular the transition in gait between swimming and stepping modes. The topology of the network is inspired by models of the lamprey CPG, complemented by additions based on experimental data from isolated spinal cords of salamanders. Oscillatory centers of the limbs are included in a way that preserves the flexibility of the axial network. Similarly to the selection of forward and backward swimming in lamprey models via different excitation to the first axial segment, we can account for the modification of the axial coordination pattern between swimming and forward stepping on land in the salamander model, via different uncoupled frequencies in limb versus axial oscillators (for the same level of excitation). These results transfer partially to a more realistic model based on formal spiking neurons, and we discuss the difference between the abstract oscillator model and the model built with formal spiking neurons.

Gait Transition from Swimming to Walking: Investigation of Salamander Locomotion Control Using Nonlinear Oscillators

This article presents a model of the salamander’s locomotion controller based on nonlinear oscillators. Using numerical simulations of both the controller and of the body, we investigated different systems of coupled oscillators that can produce the typical swimming and walking gaits of the salamander. Since the exact organization of the salamander’s locomotor circuits is currently unknown, we used the numerical simulations to investigate which type of coupled-oscillator configurations could best reproduce some key aspects of salamander locomotion. We were in particular interested in (1) the ability of the controller to produce a traveling wave along the body for swimming and a standing wave for walking, and (2) the role of sensory feedback in shaping the patterns. Results show that configurations which combine global couplings from limb oscillators to body oscillators, as well as inter-limb couplings between fore- and hind-limbs come closest to salamander locomotion data. It is also demonstrated that sensory feedback could potentially play a significant role in the generation of standing waves during walking.