Interneuron networks in the hippocampus

The hippocampus has contributed enormously to our understanding of the operation of elemental brain circuits, not least through the classification of forebrain interneurons. Understanding the operation of interneuron networks however requires not only a wiring diagram that describes the innervation and postsynaptic targets of different GABAergic cells, but also an appreciation of the temporal dimension. Interneurons differ extensively in their intrinsic firing rates, their recruitment in different brain rhythms, and in their synaptic kinetics. Furthermore, in common with principal neurons, both the synapses innervating interneurons and the synapses made by these cells are highly modifiable, reflecting both their recent or remote use (short-term and long-term plasticity) and the action of extracellular messengers. This review examines recent progress in understanding how different hippocampal interneuron networks contribute to feedback and feed-forward inhibition at different timescales.

► Multiple interneuron networks co-exist in the hippocampus. ► Interneurons belonging to the same type are often coupled by chemical and/or electrical synapses. ► Interneurons are specialized with respect to wiring and temporal processing. ► Different feedback circuits generate oscillations or resonate with oscillations in other structures. ► Feed-forward inhibition may play a key role in routing information.