Actions of identified neuromodulatory neurons in a simple motor system.

Recent work on neurons that release slow neuromodulators has revealed important generalities about the roles played by neuromodulation in motor systems. Activity of these cells can affect the cellular and synaptic properties of central pattern generating circuits, orchestrating new variations of motor patterns and sometimes coordinating their outputs with other motor patterns. Many modulatory neurons use multiple transmitters to evoke both fast and slow synaptic responses of various types in different target cells. Some modulatory cells can have a mediating as well as a modulating role, simultaneously acting as sensory neurons or components of another pattern generating circuit.