[Neuroscience] Re: Decay constants. What does "weighted" mean?

r norman via neur-sci%40net.bio.net (by r_s_norman from _comcast.net)
Thu Jan 15 11:17:00 EST 2009


On Thu, 15 Jan 2009 01:01:28 -0800 (PST), Bill
<connelly.bill from gmail.com> wrote:

>Hi,
>
>Synaptic events decay with an (bi)exponetial function. You can of
>course report the decay constant, which I understand, but what do
>people mean when they refer to the weighted decay constant?
>
>Thanks.

When a function does not show simple exponential decay, but rather has
several terms each with a different time constant, then each term has
a "weight" associated with it
   a exp(-t/t1) + b exp(-t/t2) 
where t1 and t2 are two time constants and a and b are the respective
"weights".

That is the usual meaning, but describe the use of the term in
context, or better, the citation with a material and methods sections
talking about how to calculate the values, and I can describe it
better.

Note:  an RC circuit, of course, has a simple exponential decay but
synaptic decay is complicated because of the spatial decay
superimposed on the temporal decay.  That is, the partial differential
equation of the cable equation of the dendritic tree is rather
different from the simple differential equation of an RC circuit.  Of
course, lingering synaptic activation also can complicate the decay
pattern.  That means that synaptic decay is not simple exponential
decay.





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