COMPUTATION OF LONG-DISTANCE PROPAGATION OF IMPULSES ELICITED BY POISSON-
PROCESS STIMULATION.
Moradmand, K. and M.D. Goldfinger.
Department of Physiology & Biophysics, Wright State University, Dayton,
Ohio 45401-0927 USA.
APStracts 2:0258N, 1995.
SUMMARY AND CONCLUSIONS
1. The purpose of this work was to determine if computed temporally-coded
axonal information generated by Poisson process stimulation were modified
during long-distance propagation, as originally suggested by George (1977).
Propagated impulses were computed using the Hodgkin-Huxley equations and cable
theory to simulate excitation and current spread in 100.m-diameter
unmyelinated axons, whose total length was 8.1 (25) or 101.4 (312.5) cm.
Differential equations were solved numerically, using trapezoidal integration
over small, constant electrotonic and temporal steps (0.125 and 1.0 sec,
respectively). 2. Using dual-pulse stimulation, we confirmed (Miller and
Rinzel 1981; Horikawa 1992 ) that for interstimulus intervals between 5 and 11
msec, the conduction velocity of the second of a short-interval pair of
impulses was slower than that of the first impulse. Further, with sufficiently
long propagation distance, the second impulse's conduction velocity increased
steadily and eventually approached that of the first impulse. This effect
caused a spatially-varying interspike interval: as propagation proceded, the
interspike interval increased and eventually approached stabilization. 3. With
Poisson stimulation, the peak amplitude of propagating action potentials
varied with interspike interval durations between 5-11 msec. Such amplitude
attenuation was caused by the incomplete relaxation of parameters n
(macroscopic K-conductance activation) and h (macroscopic Na-conductance
inactivation) during the interspike period. 4. The stochastic properties of
the impulse train became less Poisson-like with propagation distance. In cases
of propagation over 99.4 cm, the impulse trains developed marked periodicities
in Interevent Interval Distribution and Expectation Density function because
of the axially-modulated transformation of interspike intervals. 5. Despite
these changes in impulse train parameters, the arithmetic value of the mean
interspike interval did not change as a function of propagation distance. This
work showed that in theory, while the pattern of Poisson-like impulse codes
was modified during long-distance propagation, their mean rate was conserved.
Received 16 March 1995; accepted in final form 31 July 1995.
APS Manuscript Number J176-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 15 September 1995.