Current theories propose that memory engrams are initially stored in the hippocampus and then transferred to cortical areas for consolidation and subsequent long-term storage. However, how memory engrams emerge in the hippocampus is far from understood and is the main question, which drives my and my group’s scientific work. During the course of the last 10 years of intense research, my group efforts have been clarifying the structural, functional and dynamic properties of the different neuron types and synapses in the dentate gyrus (DG) circuitry and the cellular and molecular mechanisms underlying the synchronization of neuronal networks for the encoding of information. After setting the functional and anatomical grounds, we recently moved out to understand (1) how learning-related cell associations representing new memories emerge temporally and spatially in the DG compared to other hippocampal and cortical areas, (2) how the different neuron types (principal cells and the various interneuron types) contribute to this process and (3) what structural and functional circuit mechanisms underlie the emergence of cell associations. To address these fundamental questions we use state-of-the-art techniques including 1- and 2-photon population imaging in behaving mice, single unit recordings and in vitro electrophysiology and behavioural analysis.