  Small inhibitory neuronal circuits have long been identified as key neuronal
motifs to generate and modulate the coexisting rhythms of various motor
functions. Our paper highlights the role of a cellular switching mechanism to
orchestrate such circuits. The cellular switch makes the circuits
reconfigurable, robust, adaptable, and externally controllable. Without this
cellular mechanism, the circuits rhythms entirely rely on specific tunings of
the synaptic connectivity, which makes them rigid, fragile, and difficult to
control externally. We illustrate those properties on the much studied
architecture of a small network controlling both the pyloric and gastric
rhythms of crabs. The cellular switch is provided by a slow negative
conductance often neglected in mathematical modeling of central pattern
generators. We propose that this conductance is simple to model and key to
computational studies of rhythmic circuit neuromodulation.
