Rhythms of the hippocampal network

Local field potential recordings of the hippocampus reveal three types of neural activity rhythms: theta, sharp wave–ripples and gamma. In this Review, Colgin discusses recent findings from rodent studies that provide insight into the origin of these rhythms and their roles in memory and other behaviours. The hippocampal local field potential (LFP) shows three major types of rhythms: theta, sharp wave–ripples and gamma. These rhythms are defined by their frequencies, they have behavioural correlates in several species including rats and humans, and they have been proposed to carry out distinct functions in hippocampal memory processing. However, recent findings have challenged traditional views on these behavioural functions. In this Review, I discuss our current understanding of the origins and the mnemonic functions of hippocampal theta, sharp wave–ripples and gamma rhythms on the basis of findings from rodent studies. In addition, I present an updated synthesis of their roles and interactions within the hippocampal network.