The challenge of neuromechanical integration demands an interdisciplinary effort to match data systematically across mathematical models, numerical simulations, physical models, as well as biological experiments. Locomotion results from high-dimensional, dynamically coupled interactions between an organism and its environment. Fortunately, simple models we call templates can resolve the redundancy of multiple legs, joints and muscles. A template is the simplest dynamical system model that exhibits a targeted behavior. Extraordinarily diverse animals show the same dynamics - legged animals appear to bounce like people on pogo sticks. Force patterns produced by six-legged insects are the same as those produced by trotting eight-legged crabs, four-legged dogs and even running humans. These diverse species that differ in leg number and posture run in a stable manner like sagittal- and horizontal-plane spring-mass systems. Mathematical models show that these designs self-stabilize to perturbations without neural feedback. Templates must be grounded in more detailed models to ask questions about multiple legs, the joint torques that actuate them, the recruitment of muscles that produce those torques and the neural networks that activate the ensemble. We term these more elaborate models anchors. Since mechanisms require controls, anchors incorporate hypotheses concerning the manner in which unnecessary motion or energy from legs, joints and muscles is removed, leaving behind the behavior of the body in the low-degree of freedom template.

Guided by direct experiments on many-legged animals, mathematical models and physical models (robots), we postulate a hierarchical family of control loops that necessarily include constraints of the body’s mechanics. At the lowest end of this neuromechanical hierarchy, we hypothesize the primacy of mechanical feedback – neural clock excited tuned muscles acting through chosen skeletal postures. Control algorithms appear embedded in the form and skeleton of the animal itself. Muscles tune the system by acting as motors, springs, struts and shocks all in one. On top of this physical layer, we hypothesize sensory feedback driven reflexes that increase an animal’s stability further and, at the highest level, environmental sensing that operates on a stride-to-stride timescale to direct the animal’s body. Finally, locomotion requires an effective interaction with the environment. Amazing feet permit creatures such as geckos to climb up walls at over meter per second without using claws, glue or suction - just molecular forces using hairy toes. These fundamental principles of animal locomotion have inspired the design of new control circuits, tuned structured, artificial muscles, self-clearing dry adhesives, and autonomous legged robots such as the Ariel, Mecho-gecko, Sprawl, RHex, RiSE and Stickybot that can aid in search and rescue, inspection, detection and exploration.

Bio

Dr. Robert J. Full is Chancellor’s and Goldman Professor of Integrative Biology and Director of the Poly-PEDAL Laboratory and the Center for Bio-inspiration in Education and Research at the University of California Berkeley.

Host: Professor Jeff Moehlis