The Handbook of Brain Theory and Neural Networks

Locomotion is a fundamental skill for animals. It is required for a large variety of actions such as finding food, encountering a mate, and escaping predators. Vertebrate locomotion can take various forms including swimming, crawling, walking, flight, as well as some more idiosyncratic gaits such as hopping, brachiation, and burrowing. Animal locomotion is characterized by rhythmic activity and the use of multiple degrees of freedom (i.e. multiple joints and muscles). In vertebrates, motion is generated by the musculoskeletal system in which torques are created by antagonist muscles at the joints of articulated systems composed of rigid bones. All types of vertebrate locomotions rely on some kind of rhythmic activity to move forward: undulations or peristaltic contractions of the body, and/or oscillations of fins, legs or wings. By rhythmically applying forces to the environment (ground, water, or air), reactions forces are generated which move the body forward. This type of locomotion is in contrast to most manmade machines which usually rely on few degrees of freedom (e.g. a limited number of powered wheels, propellers, or jet engines), and continuous, rather than rhythmic, actuation. From a technological point of view, animal locomotion is significantly more difficult to control than most wheeled or propelled machines. The oscillations of the multiple degrees of freedom need indeed to be well coordinated to generate efficient locomotion. However, as can be observed from the swimming of a dolphin or from the running of a goat in irregular terrain, animal locomotion presents many interesting features, such as energy efficiency (for swimming) and agility. The next sections will review the neural and mechanical mechanisms underlying vertebrates’ fascinating locomotor abilities.