The idea of a critical period in hippocampal postnatal development characterized by hyperexcitability was a major research line in the 90s. Giant Depolarizing Potentials (GDPs) represent a prominent population event recorded in vitro and in vivo. During my PhD Thesis, I studied the microcircuit dynamics and cell type contribution to GDPs. They were considered to be generated in the CA3 hippocampal region. I discovered they were actually ubiquitous at any hippocampal area (Menendez de la Prida et al., EJN 1998), and generated by small pieces of tissue provided they contain a minimal network following a threshold dynamics (Menendez de la Prida, J Neurophysiol 1999; Physical Rev. E 1999). Using simultaneous intracellular recordings, I started exploring the contribution of different cell types to the initiation and triggering of population events (Menendez de la Prida and Sanchez-Andres, Neuroscience 2000).