Oscillations of the neuronal network are well defined in the hippocampus, with theta oscillations associated with numerous cognitive functions. The role interneurons play in hippocampal oscillations is also well defined; however, the rules governing cell type-specific firing during oscillations are not known. The goal of this study is to determine how afferent inputs are processed to produce a given output in one class of GABAergic interneurons: Hippocampus-Septum (HS) interneurons using combined three-dimensional two-photon, electrophysiological and histological/anatomical methodology.Our proposal involves groundbreaking research by studying oscillations in a complete hippocampal preparation both on the network and subcellular level. The methods and technology to be involved is above the state-of-the-art, as novel, rapid three-dimensional two-photon techniques will be applied in conjunction with multicellular and single cellular electrophysiology. The project means the continuation of a fresh collaboration using the Hungarian partner’s knowledge on two-photon single- and multicellular imaging parallel with the French partner’s basis in epilepsy and neuronal oscillations. In a 24 month undertaking, the following objectives are to be addressed:1) Rules of action potential genesis and backpropagation in HS cells.2) Active properties of dendrites in HS cells.3) Rules of synaptic integration during physiological oscillations in HS cells.4) Hyperexcitability and dendritic properties of HS cells.The combined results on imaging, electrophysiology, immunohistochemistry and methods for correlation will be applied to deduct the correct conclusions on how hippocampal oscillations affect single neurons, neuronal processes and dendritic phenomena. As a result, we will be able to gain new insight on the information processing occurring under oscillatory activity in both the healthy and pathological brain states.