The hippocampus plays a critical role in the formation of many types of memory, most notably spatial and episodic memory.
This fact was made most famously clear in the case of patient Henry Molaison (H.M.) who post-operatively was unable to form new episodic memories (anterograde amnesia). He was henceforth only living in the present moment, unable to recall past or recent episodes in his life, though he maintained his pre-operative semantic knowledge of himself and the world. Another patient, Clive Wearing, was afflicted with encephalitis that destroyed most of his hippocampus and fornix fibers connecting the hippocampus to the neocortex. Consequently, he is unable to remember anything as recent as 30 seconds ago, though he still manages to play the piano beautifully (see also the article by Oliver Sacks, and the excellent film, Memento, by Christopher Nolan).
While there is still debate regarding the extent to which the hippocampus is necessary for the maintenance of stored information, the general view of hippocampal function resulting from these and a number of animal studies, is that the hippocampus is necessary for the formation of episodic memory. A number of different lines of evidence point to neuronal reactivation during sharp-wave ripples as a key mechanism for systems memory consolidation. One of our research goals is to better understand the role that network activity during sharp-wave ripples plays in this process, during waking and sleep.