The hippocampus is a brain area that is involved in a variety of functions. In particular, the formation of memory and the codification of space depend on the functioning of the hippocampus. Virtually all areas of the hippocampus, and of most parts of the brain, contain excitatory and inhibitory neurons that form individual microcircuits. It is in the interaction between excitatory and inhibitory circuits where appropriate functional responses arise. We study how excitation and inhibition interact to activate neurons in the dentate gyrus of the hippocampus, one of the only regions of the brain in which new neurons are formed throughout life. In this seminar I will present experiments using electrophysiology and calcium imaging aiming to understand the functional role of newborn neurons in the processing of afferent stimuli, with the focus on the synaptic mechanism that generate the unique properties they present.