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synaptic plasticity question, etc.

Eric Wassermann ewass at helix.nih.gov
Mon Feb 14 11:38:40 EST 1994

In article <2jec03$qu4 at gap.caltech.edu>, rawlings at cco.caltech.edu (Jeffrey
Rawlings) wrote:
> exb0405 at csdvax.csd.unsw.edu.au (BARRY MANOR, NO DOUBT.) writes:
> >Something I'm curious about.  During the course of the adult lifetime, say even
> >from minute to minute, does synaptic topography change dynamically ?  Are
> >synapses 'broken' and formed as part of normal ongoing brain function ?
> I would say "probably."  A couple of relevant lines of research:
> 	-In developing chick optic tectum, Scott Fraser and 
> colleagues have imaged individual axonal arbors on a time scale
> of an hour (maybe finer, now).  The results:  there are different
> classes of branch points with different lifetimes, and you can
> get very significant remodeling of entire arbours over fairly short 
> time spans.  There is of course the assumption that these branches
> actually contain functional synapses, and this is in developing, not 
> adult, chick.
> 	-In adult monkey, Mike Merzenich has demonstrated large changes
> in the receptive fields and maps in somatosensory cortex following
> training of the monkey.  These changes occur (I think) on the order of 
> weeks-months, although some may be faster.  Presumably, synapses
> would have to be formed and broken on a large scale to get these changes.
Experiments in our lab with transcranial magnetic stimulation showed
expension of the cortical representation of muscles proximal to an ischemic
nerve block in the arm within minutes of cuff inflation.  Kind of like
instant Merzenich and too fast for anything but loss of inhibition from the
deafferented part of the limb representation (see papers from Brasil-Neto
et. al: Neurology 42, Brain 116).
                                      As far as I know,
Eric Wassermann                       The opinions expressed are not
Human Motor Control Section           those of the Federal Government,
NINDS, NIH                            the U.S. Public Health Service
                                      or the National Institutes of Health

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