Memory for Places Learned Long Ago is Intact After Hippocampal Damage

Teng, E. & Squire, L.R. (1999). Nature 400: 675-677.

Now this is a relatively short paper (even for Nature!), but I thought it was pretty interesting.  Basically, the authors analyze a human patient that has extensive (almost complete) damage to the hippocampus.  What is the hippocampus?  Well, besides being a funny word, it is a very important part of the brain that is involved in learning and memory.  More specifically, it is thought to be important for declarative memory, including spatial memory (where things are located, especially relative to one another).  The question is, however...Is the hippocampus necessary for the processing of new memories, the recall of old memories, or both?

Well, this is where this paper comes in.  It has been established that people with damage to this part of the brain are unable to establish new declarative memories (I'll compare declarative to non-declarative memories below).  So, they will not remember their doctors, where they live, jokes you tell them, etc.  However, it is still unclear if they are able to recall old memories.  In this paper, the authors were specifically interested in old spatial memories.

When they tested this patient (76 years old) about his home town that he grew up in the 1930's and 1940's, they found that he could "navigate" through the town as well as his classmates who moved away about the same time as the patient (now, that had to require some detective work!).  When I say "navigate", I don't mean that the authors took the patient back to the town.  Rather, they asked him questions like, "How would I get to this store from your house?" or "If you were facing this church, which direction would the high school be?"  Now, those aren't the real questions, but examples of questions they asked him.  Remarkably, although the patient could not tell the authors anything about his current living area, he could answer all the questions as well as (sometimes even better) than the control subjects about his old neighborhood!  Pretty remarkable, eh?

For me, anything about the brain is important.  I think it is such a fascinating organ whose complexities and mysteries will provide many more years of interesting research.  Many neurological and psychiatric disorders are difficult to treat since we have only scratched the surface of understanding how the brain works, from the cellular level to the behavioral level. 

This paper is especially interesting for me since it discusses how we learn and remember.  Have you ever thought how this works?  I just think this area is so cool!  Now, as I mentioned above, cognitive psychologists and neuroscientists often divide memories into one of two categories: declarative (explicit) memories and non-declarative (implicit) memories.  I won't go into too much detail here, but I really encourage you to find more detailed reviews on the subject, you won't be disappointed!  Declarative memories are those memories we most often associate with memory: learning in school, remembering names and places, where we live, etc.  In other words, memories we can easily talk about.  The hippocampus appears to play an important role in the processing of these memories (but not in the recall of these memories as demonstrated here).  Non-declarative memories are those memories that we often do not think about (which is why they are also called implicit): like emotional memories or procedural memories (riding a bicycle).  If you are frightened in a particular environment, you may feel fright once again upon visiting that environment...but you may not know why.  That's an example of non-declarative memories.  A part of the brain called the amygdala seems to be important in these emotional memories, while the another part of the brain called the cerebellum may be important in the procedural memories.  Now, whether these brain areas are also involved in the recall of these memories, I'm not sure (sorry).  But, as you can see, the field of learning and memory itself is a very complex area...but so interesting!

Okay, I hope you enjoyed this summary...and I hope you check back soon for more advances in the life sciences!  Thanks again!