11-4. Locomotion

In the classic half center model of a CPG, as proposed by Anders Lundberg and his colleagues (Jankowska et al., 1967a, b; Stuart and Hultborn, 2008), it was assumed that each limb is controlled by a separate half center and that each half center contains two groups of excitatory interneurons that directly project to flexor and extensor motoneurons, respectively. Because of the mutual inhibitory interconnections between the two groups, only one group can be active at a time (Figure 34). The CPG circuit for lamprey locomotion has recently been analyzed in depth and reconstructed by simulation (Grillner et al., 1991, 2007; Grillner and Jessel, 2009). A substantial but less complete model has also been achieved for cat locomotion (McCrea and Ryback, 2008).