In all simulations, locomotor oscillations were produced by bilateral activation of glutamatergic populations in the CnF by the variable excitatory drive, DCnF,ex. The other variable drive was applied unilaterally to the inhibitory population either within the CnF (DCnF,in, A and D) or within the PPN (DPPN,in, B and E), or within the LPGi (DLPGi,in, C and F). In (A), (B) and (C), the corresponding 2D diagrams were built for all three cases, and frequency was represented by color. (A) Unilateral stimulation of the inhibitory population in the CnF reduced locomotor frequency and stopped locomotion at higher stimulation intensities. (B) Unilateral stimulation of the inhibitory population in the PPN decreased locomotor frequency but was not able to arrest locomotor oscillations completely. (C) Unilateral stimulation of the inhibitory population in the LPGi decreased locomotor frequency and could also stop locomotion similar to the situation in (A). Black dotted lines indicate iso-frequency lines for 2, 4, 6, 8 and 10 Hz. White vertical dashed lines indicate the threshold for activation of the corresponding inhibitory populations. (D)-(F) Example traces of rhythmic extensor activities in all four RGs to illustrate changes in gait for the different stimulation parameters. An increase of inhibition in all cases was accompanied by sequential frequency-dependent gait transitions. Examples 1–5 in (D)-(F) are taken from the parameter combinations indicated by open circles (labeled 1–5) along the red dashed lines in (A)-(C). In all examples, DCnF,ex = 3.04, DCnF/PPN/LPGi,in are indicated for each simulation. lh: left hind; lf: left fore; rh: right hind; rf: right fore.