function of hippocampus

[Chris Trengove]

As a non-expert in regards to the hippocampus I would like to offer a
thought triggered by the following remarks of Minai, to see what people
think:

On Thu, 27 Aug 1998, Ali Minai wrote:
> That having been said, I do think (and others can marshall the evidence
> better than I can) that a preponderance of evidence favors a hippocampal
> involvement in episodic memory and, at least in rodents, spatial cognition.
..
> The issue of hippocampal involvement in spatial cognition in rodents...
> is given overwhelming credibility ... by the undeniable existence of
> place cells and head-direction cells. 
> ... provides
> convincing evidence that the hippocampus ``knows'' a great deal about
> the animal's spatial environment, is very sensitive to it, and responds
> robustly to disruptions of landmarks, etc. 
.. 
> I do not think we really understand what role the rodent hippocampus plays
> in spatial cognition, but it is hard to dispute that it plays some ---
> possibly many --- important roles. I think that, as theories about
> hippocampal function begin to place the hippocampus in the larger context
> of other interconnected systems (e.g., in the work of Redish and Touretzky),
> we will move away from the urge to say, ``Here! This is what the hippocampus
> does'' and towards the recognition that it is probably an important part
> in a larger system for spatial cognition.
.. 
> Finally, one issue that is particularly relevant to hippocampal theories
> is the possibility that the categories of memory (e.g., episodic, declarative,
> etc.) or task (DNMS, spatial memory, working memory, etc.) that
> we use in our theorizing may not match up with the categories relevant to
> actual hippocampal functionality. Perhaps we are trying to build a science
> of chemistry based on air, water, fire, and earth. 

  So, the above quotes concerning the role of hippocampus in categories of
memory such as episodic memory as well as tasks such as spatial cognition
suggests to me we consider from a top down, psychological standpoint why
spatial cognition and episodic memory should be tied together
functionally, and hence why we shouldn't be surprised that a single part
of the brain is involved in both.
  From my own subjective observations, if I am trying to remember a
thought that I had, or a particular piece of information that came up in a
conversation, often the best way to proceed is for me to remember where I
was when I had the thought.  Once I have remembered the place where I had
the thought I have access to a rich pool of cues that can help to trigger
the particular thought I'm after.
  It thus makes sense to me that spatial cognition should be involved in
the laying down of new memories.  In the course of a day I will have
perhaps hundreds of disctinct cognitive experiences to remember, but the
number of distinct _places_ in which I dwell whilst having those
experiences is likely to be at least an order of magnitude smaller.
  Thus it makes good sense to organise memory around the memories of the
places one has been during the course of a day.  I believe one idea in
circulation e.g. discussed by Rolls and coworkers, is that the hippocampus
provides a short term 'buffer' for storing memories, which are later
'transferred' to the neocortex for long term storage.  This idea is in a
similar vein.
  On a more general note, this kind of thinking suggests that eventually
we will find that there is a harmonious correspondence between the
functional interrelationships of certain, various aspects of cognition on
the one hand and the manner in which various brain structures (areas and
pathways) are especially involved in these aspects of cognition.  Thus the
feedback between neuroscience and psychology ought to give us insights
into the functional organisation of cognition which could not otherwise be
found; i.e. to help us to find the right categories, to go beyond 'air
water fire and earth' c.f. Minai, above.
  Back to the specific idea given above, I'm curious whether specialists
of the hippocampus find it (a) highly dubious, implausible or naive; or
(b) too obvious to be worth mentioning; or (c) a potentially useful way
to look at the role of the hippocampus.

Chris Trengove
School of Mathematical Sciences,
University of Technology, Sydney.