Working memory localization in hippocampus

F. Frank LeFever flefever at ix.netcom.com
Sun Mar 15 00:32:49 EST 1998


Sturla--

Re-read what I wrote.  I did not say anything about needing prefrontal
cortex for "intellectual functions"; instead, I emphasized that tasks
WITHOUT much in the way of "intellectual" demands (note that quotation
marks were in the original) but with strong WORKING MEMORY demands were
compromised by prefrontal dysfunction.

Your examples illustrate my point about different operational
definitions based on different species and tasks.  The rat paradigm you
cite has questionable relevance to working memory as defined by human
tasks.

re "mentalistic" terms: as a neuropsychologist, I too try to avoid
them.  "Intellectual" (in quotes) was intended to convey a
plain-language understanding of the requirements of some kinds of
tasks--i.e. requiring a complex information base, difficult to perform
for the average person, etc.  Trails B requires only knowledge only of
alphabetical order and numerical order (i.e. a,b,c,d..etc. and
1.2.3.4..etc.).  The "intellectual" demand is small as demonstrated
operationally by the subject's typically repeating the instructions 
with no difficulty, both before and after failure in executing the
task.   (This is typical of many paradoxes of the "prefrontal
syndrome".)

Frank






In <3509180b.595894 at news.ntnu.no> stumol at stud.ntnu.no (Sturla Molden)
writes: 
>
>On 13 Mar 1998 03:53:38 GMT, flefever at ix.netcom.com(F. Frank LeFever)
>wrote:
>
>>One big problem in this area is the diversity of definitions of
>>"working" memory.
>>
>>Using at least some (operational as well as explicit) definitions, I
>>believe oone can argue that the hippocampus is NOT very important for
>>Working Memory.  Part of the difference may lie in the organisms and
>>paradigms used (e.g. rats and rat tasks vs. humans and human tasks).
>

>The claim that the hippocampus and surrounding temporal-lobe
>structures are involved in episodic and/or spatial working memory is
>not to say that these are the ony structures needed for this type of
>memory (cf. patient NA).
>
>However, bilateral hippocampectomy disrupts all forms of memory
>lasting for more than 15 seconds and containing more than a dozen
>items; i.e. the structure is needed for all forms of explicite memory
>that requires plastic rather than dynamic changes in the nervous
>system.
>
>Rawlins claim that the hippocampus was a temporary memory store was
>based on such findings as the abolished partial reinforcement
>extinction effect in rats with hippocampal lesions when between-trial
>interwals were long but not when they were short (eg less than 10
>seconds).


>
>>Soomeone (I think it may have been Joachim Fuster) said the better
term
>>might be "working WITH memory".  Fuster's work (monkeys again) has
>>shown the importance of the prefontal cortex of selecting/activating
>>specific regions of posterior cortex so as to make not just transient
>>memory but long-term memory NEEDED FOR PERFORMANCE OF A TASK
>>temporarily available (and, I would argue, dominant in competition
with
>>other memories and/or ambient stimuli).  Accordingly, "working with"
>>the relevant memories can be disrupted by local cooling of either the
>>relevant frontal region or the relevant posterior region (e.g. a
>>particular part of parietal cortex).  (Again, easy to locate via
>>Medline).
>>
>>In human clinical neuropsychology, performance of tasks with
relatively
>>little "intellectual" demands but strong "working memory" demands
(e.g.
>>Trails B) is impaired with frontal dysfunction (cortical or
>>subcortical).


>
>There can be little dubt that other structures such as the prefrontal
>cortex are needed for "intellectual functions" (as a biologist I try
>to avoid these mentalistic terms); but hippocampal lesions
>nevertheless disrupt the animals performance in working memory
>dependent tasks (and this is not due to perceptual or motorical
>dysfunctions). The exact function of the hippocampus remain to be
>discovered, but it is clearly essential for the operation of certain
>forms of memories (those that have a spatial component).
>
>
>Sturla Molden
>
>
>
>
>
>




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