Memory (and SOMs)

Matt Jones jonesmat at physiology.wisc.edu
Mon Feb 18 12:37:52 EST 2002


"yan king yin" <y.k.y@(dont spam)lycos.com> wrote in message news:<ZB2b8.467$B92.91629 at news.xtra.co.nz>...


> > I agree with this too. For example, one area in the brain thought to
> > be critical for consolidation of short-term memory is the hippocampal
> > formation and associated entorhinal cortex. The iterative structure
> > looks like this:
> 
> You should be careful that consolidation is different from recall, and
> the hippocampus is required for consolidation, but not recall. There
> is also the additional complication that hippocampal lesions usually
> result in a few years of retrograde amnesia as well.

Perhaps consolidation is different, and perhaps not. How does an
experimenter know whether a memory has been consolidated unless the
test subject is also able to recall it? Either way, the hoippocampus
appears to be important in recall of memories that have just been
acquired (short-term). The famous example of being able to remember 7
plus or minus 2 digits of a phone number is sensitive to hippocampal
damage.


> I suppose you're talking about memory recall here, but hippocampus
> is not involved in recall of long term memories. Though you may argue
> that this is the recall mechanism of recent memories that is stored in the
> hippocampus.

Right. I think everyone agrees that long-term storage is somehow
distributed around cortex, not in hippocampus. Also, there are several
kinds of memories that appear to be little if at all affected by
hippocampal damage.




> 
> Another simplified schematic pathway is as follows: cortex -> EC ->
> dentate gyrus -> CA1 -> CA3 -> Subiculum -> EC -> cortex, where
> CA=hippocampus. So it looks like a loop and memory might pass through
> this loop to be stored in the cortex. It is also possible that memory is
> processed in other parts of the cortex and the hippocampus only
> mediates the consolidation process.

I think you mean dentate->CA3->CA1...


> 
> I think the central question is in where and how is memory stored
> in the cortex. 

I do not necessarily think that is the central question. The long-term
storage might be the very last step in the process. Lots of other
steps are probably very important. For example, decisions about which
experiences are worth storing and which are not are probably pretty
important steps. We don't store everything, only some things. Some
theories suggest that the selection of events for storage takes place
in hippocampus, and involves a comparison of new information with
previously buffered information. If the new information is
sufficiently different, then it gets processed and eventually stored.
If it's very similar to previous information, it may get ignored
because there's already a copy of it. There is a dual role of memory
processing at work, where similar information gets compressed into a
single representation, whereas novel information gets differentiated
from previous information. The hippocampus appears to be involved in
both of these processes, without which the cortex would just fill up
with a lot of extraneous information that isn't much use to the
animal, and was stored in a very inefficient manner.





>lished, but I saw his Neuroscience poster.
> 
> This sounds similar to the idea that the hippocampus forms a "cognitive
> map" of the environment.
> 


Yeah, I think the SOM work, and many other modeling efforts, are
attempts to develop a computational mechanism by which such cognitive
maps may be implemented.


cheers,

Matt




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