Hippocampal gamma-frequency oscillations: from interneurones to pyramidal cells, and back.

GABAergic interneurones are necessary for the emergence of hippocampal gamma-frequency network oscillations, during which they play a key role in the synchronization of pyramidal cell firing. However, it remains to be resolved how distinct interneurone subtypes contribute to gamma-frequency oscillations, in what way the spatiotemporal pattern of interneuronal input affects principal cell activity, and by which mechanisms the interneurones themselves are synchronized. Here we summarize recent evidence from cholinergically induced gamma-frequency network oscillations in vitro, showing that perisomatic-targeting GABAergic interneurones provide prominent rhythmic inhibition in pyramidal cells, and that these interneurones are synchronized by recurrent excitation. We conclude by presenting a minimal integrate-and-fire network model which demonstrates that this excitatory-inhibitory feedback loop is sufficient to explain the generation of intrahippocampal gamma-frequency oscillations.