How the brain's internal clock system uses genes, nerve cells, and circuits to keep time

The suprachiasmatic nucleus (SCN) functions as a ∼24 h clock both in living animals and in isolated culture.

• The transcriptional architecture of circadian clocks is consistent across different species.
• Mammalian interneuronal mechanisms provide enhanced integration of circadian signals.
• Recent findings explore how electrical activity and calcium levels within SCN neurons relate to intracellular clocks.
• Investigations into neuron and glial cell roles reveal their contributions to the encoding of circadian time.
• Mechanisms at the epigenetic and circuit levels help the SCN convert light signals into daily rhythms.

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