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Ten Percent Myth

Matt Jones jonesmat at physiology.wisc.edu
Tue Feb 12 13:51:53 EST 2002


"John H." <John at overhere> wrote in message news:<ln6a8.17640$N31.885925 at ozemail.com.au>...
> "Matt Jones" <jonesmat at physiology.wisc.edu> wrote in message
> news:b86268d4.0202111323.1a3c42ea at posting.google.com...
> > "John H." <John at overhere> wrote in message
>  news:<7Ra98.16263$N31.800561 at ozemail.com.au>...
> >

> http://www.ldolphin.org/constc.shtml
> 
> Couple of articles at above link allow download of relevant papers.
> 
> Series of links here, the idea is still controversial and hit the airwaves
> last year in a big way. Actually I don't mind this sort of thing, suits my
> cynicism towards absolutes ... . Anyway, what's so special about light that
> it should be constant?



Thanks for the references. I guess the ones about "slowing" light
aren't too objectionable because they all slow it by making it travel
through some medium, not a vacuum. The ones about "speeding" it
through a medium are sort of disquieting, as are the ones about the
speed of light changing over time.


I don't know why this bothers me. Maybe it's because if the speed of
light  -isn't- constant, then a lot of physics that has been shown
empirically to be predictable and derivable from special and general
relativity doesn't make sense anymore. Does anybody know of a worked
out theory that allows the speed of light to vary, and still have
everything fit together properly? Does superstring theory allow that
to happen?





 






> 
> John H.
> 
> By the way Matt, read your webpage sometime ago and was fascinated by the
> idea of a single Gaba neuron entraining hundreds of neurons (hippocampus I
> think). Hmmm, that's gotta be important. Care to throw any light on this?
> 



The best citation that  comes to mind is this one:

Cobb SR, Buhl EH, Halasy K, Paulsen O, Somogyi P.	Related Articles
Synchronization of neuronal activity in hippocampus by individual
GABAergic interneurons.
Nature. 1995 Nov 2;378(6552):75-8.

which is a really great demonstratoin, but I'm not sure if it was the
very first demonstration.


I agree that this must be important. The mechanism of synchronization
is as follows: Gabaergic interneurons have highly branched axons that
contact hundreds or thousands of principal cells. So a spike in the
interneuron evokes a synchronous IPSP in -each- of its targets. This
IPSP halts or delays firing for a brief period, similar in all target
cells, after which all the targets are able to fire, and they
therefore fire synchronously.
In addition, simply hyperpolarizing a neuron can lead to "rebound"
spikes, so the synchronous IPSPs don't just delay ongoing firing, they
partially -promote- a synchronous spike.

All this leads to some rhythmic population behavior, because the
principal cells also make excitatory synapses -back- onto the
Gabaregic neurons. So the synchronous spike in the principal cells
then excites a whole bunch of Gabaergic neurons, which fire spikes,
hyperpolarizing their targets and leading to another round of rebound
spikes. The period of the rhythmicity is directly related to the
duration of the IPSPs (and thus to the biophysical properties of
GABA-A receptors).

One way that this might be important is to participate in generating
the well-known theta and gamma rhythms observed in hippocampus and
cortex, and which are associated with specific behavioral states
(e.g., exploration, learning, REM sleep). One idea is that these
rhythms act as clocking signals to sequence the flow and timing of
information, and to "bind" together the activity of neurons encoding
different aspects of the same stimulus. For example, neurons that
encode "red" and those that encode "car" might be synchronized so that
we perceive the unified object  "red car" instead of just the separate
attributes.

Cool stuff.




Cheers,

Matt




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