hippocampus function

Sturla Molden sturla.molden at svt.ntnu.no.--.delete.this
Mon Mar 27 09:33:48 EST 2000

On Sun, 26 Mar 2000 07:10:48 -0800, LAURA
<lauraritchie79NOlaSPAM at hotmail.com.invalid> wrote:

>Can anyone help? I am looking for a publication which neatly
>condenses and summarizes the hippocampal functions into
>"nice" manageable chunks. I am studying for my psychology
>degree and any aid would be greatly appreciated!

There are a number of theories of hippocampal function,
none of which are statisfactory. Typical contemporary models
of hippocampal function come in three classes:

1. "Memory models" typically emphasise human amnesia
associated with hippocampal neuropathology, e.g. the
"declaratve memory" by Larry Squire, Stuart Zola, Howard
Eichenbaum, et al.

2. "Spatial models" are derived from animal studies, e.g. 
single-unit recording, selective lesions, and behavioural
ecology. The typical controversy is whether the hippocampus
is involved in allocentric navigation, dead reckoning, or both.

3. "Computational models" are derived form connectionist theory
and typically belong to a class of neural networks called

The problem with "memory models" is that they are derived from invalid
studies, e.g. studies of human patiens that have experienced cerebral
ischemia. Cerebral ischemia produces effects that are different from
those of selective hippocapal lesions, e.g. deficits on the delayed
nonmatching-to-sample test which do not depend on hippocamal
integrity. The animal experiments that have seemed to
support this hypothesis have either been bady performed  or
insufficiently controlled. The problem with "spatial models", although
more consistent with the data than memory models (both in animals and
humans), is  the empirical fact that hippocampal lesions seem to
disrupt some tasks that are of "non-spatial" nature. These include
trace conditioning and latent inhibition. The problem with
"computational models" is that they are so premature and simplified
that they seldom allow any testable predictions to be drawn.

To my knowledge, no book chapter cover all three aspects of
hippocampal models. You could for example see issue 4 vol 9
(1999) of the journal "Hippocampus" for a debate on the information
encoded by single units. There are also several interesting
intoductory reviews in MIchael Gazzanigas recent antology 
"The New Cognitive Neurosciences" (MIT Press, 1999), read e.g. the
chapters by Matthew Wilson, Bruce McEwen, Larry Squire and Barabara
Knowlton, and David Sherry.


Sturla Molden

PS. To be fair a fourth class of hippocampal models, "the behavioural
inhibition theory" by Jeffrey Gray, grew out of the behaviourist
tradition, but have been as good as discarded on empirical grounds. It
is nevertheless still  encountered in some neuropsychology texts (even
very recent ones) although seldom or rever seen in the scientfic
journals (except for historical review papers). If you are studying
psychology you may therefore get familiar with it, but bevare that it
belong on the junk yard of empirically fasified theories.



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