Hippocampus and Learning
jwoodson at ucla.edu
Sat Nov 9 13:53:14 EST 1996
NEW: The phenomenon(s) of long term sensitization or even of long-term
potentiation (LTP) in the hippocampus point toward a putative and highly
debatable mechanism of neural plasticity underlying learning. Both forms
of adaptation have been found in the hippocampus. However, no one has
completely justified LTP as a mechanism of STORAGE. In fact, it may be
induced more effectively by high frequency trains of pulse stimuli than by
associative (pre & post synaptic) convergent stimuli, although this is
still the subject of much debate. If this is so, is LTP a mechanism of
association and coincidence detection, or is it mechanism for the
maintenance and storage of learned associations? I would propose the
former, although I am by no means an expert on the topic. Perhaps Eric
Kandel would have more to say. Differences in LTP in the hippocampus and
in the cortex vary with the particular region studied (e.g., CA1 vs CA3),
but seem to share many of the same mechanisms of induction, expression, and
I am intrigued by a more recent allusion to storage of memory traces in
oscillatory subcycles of neural activity proposed by John Lisman and Marco
Idart, (1995) Science, Vol 267, p 1512 - 1515. It would be interesting to
see the results of empirical studies integrating such theories with what is
known about LTP.
>If what you wrote below was entirely correct, then how would you explain
>the results that started to come out of Disterhoft's lab at NWU ten years
>ago (and have continued to be replicated in various ways right down to
>today) whereby hippocampi removed from the rabbit 24 hrs to subsequent to
>classical conditioning of the nictitating membrane reflex, show biophysical
>changes in K+ conductances within individual CA1 cells, that are
>learning-specific (ie, appear only in isolated hippocampi from conditioned
>rabbits, but not in the isolated hippocampi of control rabbits--both
>explicitly unpaired groups and naives). I tend to agree with you
>intellectually, but the empirical data out there needs to be delt with.
>Jim Olds Jr.
James Woodson* (jwoodson at ucla.edu)
Dept. of Psychology - Behavioral Neuroscience
University of California at Los Angeles
405 Hilgard Ave.
Los Angeles, CA 90095
"It is not what the man of science believes that distinguishes him,
but how and why he believes it. His beliefs are tentative, not
dogmatic; they are based on evidence, not on authority."
- Bertrand Russell
*Research in Learned Helplessness, Adenosine,
Anatomical Sex Differences in the Brain (SDN-POA), and Sexual Motivation
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