Xiang Mou
Circadian rhythmicity in gene expression and physiological process has been observed both in the central nervous system and in the periphery, including the hippocampus. As a center for memory formation and storage, the hippocampus shows circadian rhythmicity in clock gene expression and synaptic plasticity. Circadian variation in performance of hippocampus-dependent memory task suggests a link between clock gene oscillation and behavioral response. Yet the discrepancy in time scale between fast information encoding during memory acquisition and much slower circadian oscillation in cellular processes casts doubt on the underlying mechanism of circadian regulation of learning and memory. This short review suggests that instead of being a modulator of learning process and memory formation, the time-of-day information itself could be integrated as a component of episodic memory for later consolidation and retrieval.