Figure 9.

Mechanisms of anterior-posterior coordination. (A) Minimal network capable of driving locomotion in each of the solutions from the “simple” group: M14 for VD⊢⊣DB⁺¹ (A1), M15 for DA⊢⊣AS⁺¹ (A2), and M6 for AS⊢⊣VA⁺¹) (A3). Arrows represent excitatory chemical synapses. Connections ending in circles represent inhibitory chemical synapses. Connections with line endings represent gap junctions. (B) Kymographs for each of the minimal configurations above show coordinated bending waves through the body. The intensity of red and blue depict dorsal and ventral curvature, respectively. The color-coding is the same as the one used in Figure 4A. (C) Entrainment analysis for each of the solutions reveals the directionality of the coordination among the subunit rhythmic pattern generators. The purple trajectory depicts the shift in phase that occurs in the posterior-most unit when the phase of the anterior-most unit is displaced. The brown trajectory depicts the shift in phase that occurs in the anterior-most unit when the phase of the posterior-most unit is displaced. In solutions M14 and M15, the anterior-most neural unit is capable of entraining the posterior-most neural unit but not the other way around (C1,C2). This suggests the coordination afforded by these two gap junctions is directed posteriorly. On the contrary, in solution M6, it is the posterior-most neural unit that can entrain the anterior-most unit and not the other way around (C3). This suggests the coordination afforded by this gap junction is directed anteriorly.