Fig. 6.

Activity regimes depend on drive in the reduced model. A: frequency heat map obtained by independently changing drives to the flexor and extensor half-centers. Only frequencies where the flexor and extensor are rhythmically active in strict alternation (1:1) are color coded. White areas correspond to nonphysiological regimes of burst alternation (1:n or n:1) (example shown in E) and to the states when the flexor and/or extensor are tonically active or silent (example for both tonic shown in H). B: the alternating (1:1) oscillations result from a wide range of drive combinations and underlying intrinsic activity regimes of the flexor and extensor units. Dashed lines indicate where the intrinsic activity state switches from bursting to tonic. C–H: example traces of flexor (red) and extensor (blue) units generated at drive levels indicated by black squares in A, showing network activity at low, symmetric drives demonstrating the gap between two active states (C); intermediate, symmetric drives (D); asymmetric drives yielding nonphysiological (1:n) bursting (E); asymmetric drives yielding network oscillations due to intrinsic bursting in the flexor half-center with the extensor half-center in a tonic mode (F); high, symmetric drives for which the network exhibits half-center oscillations, although both flexor and extensor are intrinsically tonic (G); high symmetric drive yielding tonic network activity (represented by sustained elevated voltage) (H).