What have neural networks achieved?

[Ken Miller]

>>>>> "-" == Terry Sejnowski <terry at salk.edu> writes:

-> Regarding the comment by Ken Miller, the regions of the cortex that
-> surround the hippocampus, including the entorhinal cortex, the
-> perirhinal cortex and the parahippocampal cortex are staging areas
-> for converging inputs to the hippocampus.  Stuart Zola has shown
-> that the severity of amnesia folowing lesions of these areas in monkeys is
-> greater as more surrounding cortical areas are included in the lesion.  
-> The famous case of HM had surgical removal of the tmeporal lobe which 
-> included the areas surrounding the hippocampus.  The view in the field is no
-> longer to think of the hippocampus as the primary site but as part
-> of a memory system in reciprocal interaction with these cortical
-> areas.  

It's clear from the lesion studies that the surrounding pieces of
cortex are involved in memory.  The problem is, what's the evidence
that hippocampus itself is involved in memory? -- given that when
Mishkin lesions hippocampus, there is no deficit in visual recognition
or spatial memory.  Is the main evidence just that it's in heavy
recipricol interaction with the places that *are* implicated by lesion
studies in memory?

Randy O'Reilly suggested Mishkin's results could be explained by
postulating the overlying cortex can handle 'familiarity', and that is
enough for the memory tasks studied.  Whether it is enough for those
tasks is a separate question, but even if so the logic, if I
understand it right, seems a little tortured to me (though not
impossible): lesioning overlying cortex affects measurements of memory
bacause it destroys all those inputs to hippocampus; yet lesioning
hippocampus itself doesn't affect those same measurements of memory
bacause the overlying cortex can do some weak memory-like things by
itself.  It seems a pretty convoluted set of reasoning to preserve the
idea that hippocampus is critical to memory, compared to the simpler
conclusion that the overlying cortex is critical to memory and
hippocampus just isn't involved.

So again, is there positive evidence for *hippocampal* involvement
in memory?  There may well be some, but I don't think I've heard it
yet ... 

don't mean to be argumentative, just really wondering ... 

Ken
 
        Kenneth D. Miller               telephone: (415) 476-8217
        Dept. of Physiology		fax: (415) 476-4929
        UCSF                            internet: ken at phy.ucsf.edu
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