leaky integrator

Thomas Chimento chimento at ursa.arc.nasa.gov
Mon May 24 11:46:48 EST 1993

In article <C7E22q.3uH at murdoch.acc.Virginia.EDU>, cp5m at cajal.med.Virginia.EDU (Colin Prepscius) writes:
|> Articles by Softky & Koch, 93, and Levine, 91, (and many more) describe  
|> modeling of neurons by a "leaky integrator", or "integrate and fire model".   
|> These are essentially capacitive models of neurons, but they all seem to  
|> include "reset"; after the neuron fires, its input (voltage) is set back to 0  
|> (or resting potential).
|> My question is:  to what extent is this "reset" biologically plausible?  It  
|> seems to me that such a reset is very different from a refractory period.   

Such a reset is somewhat different from a refractory period, but if defined
carefully can be rather close to one. There are two components of a 
refractory period: absolute and relative. In the absolute, no firing may
occur regardless of input magnitude. In relative, the threshold has been
raised requiring greater stimulus for firing. During the relative refractory
period the internal potential is below resting, and it could be argued that 
a model should include this detail. All models are approximations of 
reality, and until an individual is interested in examining the consequences
of that parameter on cell or network operation,it is most efficient to keep
it simple. 

A program called NEURON written by Michael Hines at Duke U. does a 
nice job of including most of the details one would want to examine.
But this program is designed to examine single cell operation using
1-dimensional compartmental modeling. It would not be practical to 
use such a system on large networks of cells on MOST computers (today).
This program specifies channel features and is more close to 'reality' 
than a simple 'reset' definition.

*Thomas C. Chimento Ph.D.  Internet: chimento at pioneer.arc.nasa.gov *
*NASA, Ames                   Phone: 415-604-0376 (and Voice Mail) *
*Biocomputation Center          Fax: 415-604-3954                  *
*MS 239-11                                                         *
*Moffett Field, CA  94035-1000                                     *
*   My thoughts, only my thoughts, and nothing but my thoughts.    *

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