LTP LTD

[Yaakov Metzger]

Hi
Regarding your question on the net about LTP and LTD, I guess you might be
interested in my MSc thesis, published in:


AUTHOR =  {Y. Metzger and D. Lehmann},
TITLE = {Learning Temporal Sequences by Local Synaptic Changes},
JOURNAL = {Network},
VOLUME = {Vol 1},
PAGES = {169--188},
YEAR = 1990}

We present there some considerations around the nature of LTP and LTD.


I'd also like to know what aspects of LTP and LTD you are looking at,
and what other answers you got. Please mail me your answer even if you post it
because I dont scan the net too often.


Coby


From: granger at ics.uci.edu
Status: RO


I and my colleages at U.C. Irvine have done some computational modeling
of LTP in the olfactory system and in hippocampus.

The following article is based on computational analysis of network-level
effects of LTP as it occurs in the olfactory cortex.  The incremental
strengthening of synapses, in combination with lateral inhibitory activity,
led to a computational "clustering" effect; repetitive cyclic activity of
the olfactory bulb-cortex system led to sequential hierarchical information
emerging from the system:

Ambros-Ingerson, J., Granger, R., and Lynch, G. (1990).
Simulation of paleocortex performs hierarchical clustering.
{\em Science}, 247: 1344-1348.

 [LTP in olfactory paleocortex was shown by Jung et al., Synapse, 6: 279 (1990)
 and by Kanter & Haberly, Brain Research, 525: 175 (1990).]

The Science article led to specific behavioral and physiological predictions 
which were tested with positive results, reported in:

Granger, R, Staubli, U, Powers, H, Otto, T, Ambros-Ingerson, J, & Lynch, G. 
(1991).  Behavioral tests of a prediction from a cortical network simulation.
{\em Psychological Science}, 2: 116-118.

McCollum, J, Larson, J, Otto, T, Schottler, F, Granger, R, & Lynch, G. (1991).
Short-latency single-unit processing in olfactory cortex.
{\em J. Cognitive Neurosci.}, 3: 293-299.

These and related results are summarized and reviewed in:

Granger, R., and Lynch, G. (1991).
Higher olfactory processes: Perceptual learning and memory.
{\em Current Biology}, 1: 209-214.

LTP varies in its effects in different anatomical regions, such as the distinct
subddivisions of the hippocampal formation; possible effects of these different
variants of LTP and interactions among the regions expressing them are explored
in:

Lynch, G. and Granger, R. (1992).
Variations in synaptic plasticity and types of memory in cortico-hippocampal
networks.  {\em J.~Cognitive Neurosci.}, 4: 189-199.

Larson & Lynch, Brain Research, 489: 49 (1989) showed that synapses due to
different afferents all converging on a single target cell become
differentially strengthened (potentiated) via synaptic long-term potentiation
(LTP) as a function of the order in which the afferents are activated within a
time window of about 70 msec.  It might be expected that the latest arrivers
would coincide with the maximal depolarization of the target cell and thus by a
"Hebbian" argument would be most strengthened (potentiated), yet it is in fact
the earliest arriving afferents that become most potentiated, and the later
arrivers are least potentiated.  This enables the cell to become selective to
different sequential activation, i.e., to act as a form of sequence detector.
This is described in a forthcoming paper accepted in P.N.A.S. (to appear):

Granger, Whitson, Larson & Lynch (1992):
Non-Hebbian properties of LTP enable high-capacity encoding of temporal
sequences.  {\em Proc Nat Acad Sci USA} 1992, (in press).

Some of these results are briefly summarized in:

Anton, P., Granger, R. and Lynch, G. (1992).
Temporal information processing in synapses, cells and circuits.
In: {\em Single neuron computation}, 
(T.McKenna, J.Davis and S.Zornetzer, Eds.), NY: Academic Press, pp. 291-313.

Hope this is helpful; I'd be happy to provide more information and additional
papers if you wish.

-Richard Granger
 Bonney Center
 University of California
 Irvine, California 92717