Fast network oscillations in the hippocampus

Neuronal networks often express coherent oscillatory activity. These rhythms can pro­vide a temporal reference for the activity of single neurons and allow the formation of spatiotemporal activity patterns with a de­fined phase relationship of action potentials. In a single brain nucleus, oscillations at dif­ferent frequencies might be simultaneous­ly generated, but isolated rhythms might also be characteristic for specific functional brain states. During the last two decades the mam­malian hippocampus has become an impor­tant model system for the study of neuronal network oscillations. In this brain area, cel­lular mechanisms underlying neuronal syn­chronization have been described, but also models were developed to explain the con­tribution of oscillations in encoding, con­solidation, and recall of memories. Neuro­nal rhythmic activities provide an impor­tant field of analysis bringing together cel­lular mechanisms and systemic functions of the brain. Here, we use a particularly fast type of neuronal oscillation, hippocampal “rip­ples”, as an example to outline current knowl­edge and open questions related with this re­search field.