Basic Concepts of the Control and Learning Mechanism of Locomotion by the Central Pattern Generator

Basic locomotor patterns of living bodies, such as walking and swimming, are produced by a central nervous system that is referred to as the CPG (central pattern generator). In vertebrates, the CPG is located in the spinal cord and a burst signal from the brainstem induces a periodic activity in the CPG. The firing pattern of the CPG is strongly affected by sensory feedback signals from the musculoskeletal system; with the help of these feedback signals, the CPG synchronizes with body movement and accordingly send motor commands to motor neurons at an appropriate time in a movement cycle. Although it has been known that higher centers are also involved in the control of locomotion, particularly in higher vertebrates such as cats (Takakusaki et al., 2004), some experiments on spinal animals have revealed that only the CPG in the spinal cord can generate a basic motor command (Kandel et al., 2000). Although the neural circuit of the CPG would be genetically determined at a significant level, some studies such as those on spinal cats suggest the existence of a learning mechanism in the CPG (Rossignol & Bouyer, 2004). How does the CPG learn and generate proper motor signals for locomotor patterns? Considering the answer for this question would not only help the understanding of learning control system of living bodies but also bring a hint to make legged robots. In fact, some studies using computer simulation and legged robots have indicated the robustness of locomotion by using the concept of the CPG (Taga et al., 1991; Fukuoka et al., 2003). In this chapter, we introduce basic concepts of the control and learning mechanism of locomotor patterns produced by the CPG.