Memory is a strange thing. It's a conglomeration of senses and emotions that combine to create a mental duplicate of a situation. But how do we create memories? Where do we store them? Why does seemingly random stimuli evoke all-but forgotten memories? These questions have no easy answer, but the hippocampus memory theory from chapter 3 of the Lilienfeld text seems to paint the most complete picture.
The hippocampus memory theory states that memories are sent to the hippocampus, where they are stored before being transferred elsewhere long-term. This helps to explain why something that happened 5 minutes ago surfaces quickly, while an incident from 5 years ago doesn't. After all, localizing our short term memories in one place makes them easier to conjure up. Incidentally, it also backs up a leading theory behind the bizarre phenomenon of déjà vu: the brain sends a short-term memory to the hippocampus twice instead of once, resulting in that unnerving feeling that you've done something before even if you haven't (Clark & Bryant, 2009).
Another theory, the multiple trace theory, is also quite interesting, but it doesn't hold up quite as well. Basically, it asserts that memories are initially stored in multiple areas of the brain. These memories either "take root" or "wither away" over time, leaving multiple traces behind (hence its name). It makes sense that memories would originate where the sense originated (visual recollections in the visual cortex, for example); however, if that information isn't then sent to a central location to be "packaged" so to speak, it seems our memories would be very disjointed. It also doesn't explain why someone with damage to his hippocampus has trouble making new memories, but not remembering older ones (Lilienfeld, 2011).
All in all, the hippocampus theory makes the most sense. When I cram for a test an hour or so beforehand, I almost always remember the information by visualizing what I wrote in my notes or read in my textbook. This is consistent with the hippocampus' role in spatial memory (Lilienfeld, 2011). Come the final, however, I usually have to relearn information that didn't become long-term memory. This distinction between short-term and long-term memory validates the hippocampus theory, but it also leaves unanswered questions. How long does short-term memory last? Is the transfer of memory from hippocampus to cortex gradual, or like the flip of a switch? These questions continue to pique my interest, and thanks to my hippocampus, I'll be sure to remember the answers to them once I find them!
If you're interested, here's a link to a podcast on déjà vu:
(And if that doesn't work, it's the Stuff You Should Know episode from March 24th, 2009. You can find it on iTunes.)
Chapter 3 of the Lilienfeld text
Clark, J., & Bryant, C. (Writer). (2009, March 24). How déjà vu works [Audio podcast]. Stuff You Should Know.