Sensorimotor functions and stability structures in emergent hindlimbs locomotion of decerebrate cats

This study aims to reduce the complexity of machine design, motion planning, control, and advanced adaptation to the environment in quadrupedal locomotion by using the emergent behavior observed in animals. We investigate the underlying principles for the emergence of quadrupedal locomotion in terms of structure, stability, and fluctuations by simulating generation and transition of the rhythm and gait observed in decerebrate cats. In this work, we show that the principles are clarified and expanded compared to those in our previous work by incorporating a single lift-off timing determination condition into the rhythm-generating part of the controller. In belt-driven locomotion on a treadmill using the spinal cat model, the sensorimotor functions of each leg autonomously generate locomotion patterns in response to belt speed while ceasing to coordinate with the contralateral leg. In self-propulsive locomotion on the floor using the midbrain cat model, the transition after the destabilization and critical fluctuations is observed in potential functions in response to increased locomotion power, and a single trigger function for coordination induces the stabilization. In both types of locomotion, the rolling motion perturbed by increasing speed initiates a transition from out-of-phase to in-phase running. Subsequently, the new lift-off condition causes a change of the stability structure and stabilizes the transitional gait afterward, either spontaneously or explicitly via the trigger. As a result, such principles become clearer that trunk oscillations inducing the rhythm and gait, being stabilized through the gait transition, sustain rhythmic motion. This perspective could help reduce the complexity inherent in quadrupedal locomotion.