The complexity of small circuits: the stomatogastric nervous system

•Analysis of small circuits reveals interacting dynamics at different time scales.•Synaptic and intrinsic properties, neuromodulation, and long-term regulation interact.•Neuromodulation ties together short-term flexibility and long-term stability.•Circuit parameters are variable, but correlated to ensure stable function.

The crustacean stomatogastric nervous system is a long-standing test bed for studies of circuit dynamics and neuromodulation. We give a brief update on the most recent work on this system, with an emphasis on the broader implications for understanding neural circuits. In particular, we focus on new findings underlining that different levels of dynamics taking place at different time scales all interact in multiple ways. Dynamics due to synaptic and intrinsic neuronal properties, neuromodulation, and long-term gene expression-dependent regulation are not independent, but influence each other. Extensive research on the stomatogastric system shows that these dynamic interactions convey robustness to circuit operation, while facilitating the flexibility of producing multiple circuit outputs.