[Neuroscience] Re: Distant connections between neurons

feedbackdroids at yahoo.com feedbackdroids at yahoo.com
Fri Mar 31 11:52:35 EST 2006


ganges wrote:
> Can neuroscince tell the fucntional significance of long range connections.
> What is the signifincance of local densed connections, Long range
> connections etc?
> Any idea?
>
> Having long range connections has any link to small world networks(Dynamical
> sytems terminology)
>
> waiting for some one's reply
> Gangadhar.G
>


In fact, this is a good observation, and probably true. There are many
"levels" of processing in the nervous system, but even so, behavioral
responsivity times are quite fast. EG, by rough estimates from people
like vanEssen, there are maybe 10-13 levels just in the visual system
alone. And this is just on the sensory side, and not counting any
central processing beyond vision or the several levels of processing on
the motor response side. If the system of the brain were simply one
level after another after another of more or less "linear" processing,
then it would take a long time for an animal to respond to external
stimuli.

The way this problem is apparently shortcut is by the presence of many
reciprocal feedback pathways that exist between cortical regions in the
white matter. Edelman in his several books has pictures showing 50+
cortical areas in the cat cortex interconnected by 1000+ feedback
pathways. This is a very high degree of connectivity. These pathways
turn the system from a sort of "linear" arrangement into something more
like a small-world network that you mentioned, and you know from the
dynamics of small-world networks that adding just a few global
cross-connections greatly reduces the time it takes signals to traverse
the network. So, this is how you can get fast responsivity in a complex
system with many processing levels.



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