Neuroscience Forefront ReviewIn synch but not in step: Circadian clock circuits regulating plasticity in daily rhythms

- SCN clock neurons interact with one another to regulate network properties.
- SCN coupling involves multiple signaling mechanisms that remain ill defined.
- Plasticity in circadian behavior may provide insight into SCN coupling.
- This review highlights forms of circadian plasticity indicative of coupling.
- Conceptual models of coupling are proposed that can be tested in future work.

The suprachiasmatic nucleus (SCN) is a network of neural oscillators that program daily rhythms in mammalian behavior and physiology. Over the last decade much has been learned about how SCN clock neurons coordinate together in time and space to form a cohesive population. Despite this insight, much remains unknown about how SCN neurons communicate with one another to produce emergent properties of the network. Here we review the current understanding of communication among SCN clock cells and highlight a collection of formal assays where changes in SCN interactions provide for plasticity in the waveform of circadian rhythms in behavior. Future studies that pair analytical behavioral assays with modern neuroscience techniques have the potential to provide deeper insight into SCN circuit mechanisms.