Identification of the Impulse-Response Functions of a Non-Reflecting Monopolar Neuron and Its Parts
Valenzuela, Claudio Ignacio
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https://hdl.handle.net/2142/77669
Description
Title
Identification of the Impulse-Response Functions of a Non-Reflecting Monopolar Neuron and Its Parts
Author(s)
Valenzuela, Claudio Ignacio
Issue Date
1988
Department of Study
Physiology and Biophysics
Discipline
Biophysics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Neuroscience
Engineering, Biomedical
Biophysics, General
Language
eng
Abstract
In order to understand mechanistically how neurons process information, it is necessary to know how postsynaptic potentials and currents are propagated and integrated. In the present work the propagation of current was analyzed by introducing a "current" cable equation to standard ("voltage") cable theory. Also, the concepts of characteristic impedance, Z$\sb0$, and propagation factor, $\gamma$, of transmission line theory were instrumental in determining the propagation of both current and voltage signals, including those of their reflections. The latter were proven to be due to inhomogeneities in the distributed impedance of an otherwise uniform cable.
The processes of propagation and integration were assumed linear. Thus, the complete identification of the passive electrical behavior of a non-reflecting monopolar neuron stimulated at its soma was achieved by means of a quintuplet of mechanistic impulse-response functions. With the latter, both propagation and integration were performed as convolutions.
A general algorithm for deconvolution was developed for the empirical estimation of either the impulse-response function mentioned above or an unknown neuron's input function. The method works under conditions that: (1) minimize the duration of (and consequently the perturbation caused by) the identification experiments, and (2) allow the use of physiological (as opposed to artificial) probing signals.
An exact method (involving no approximations or truncation of series, for example) was developed for the empirical estimation of the non-reflecting monopolar neuron's parameters. The method involved the first three moments with respect to the origin of the (empirically determined) neuron impulse-response function $\sb{\rm V}$H$\sb{\rm SS-NRCAD}$(x,t)$\vert\sb{\rm x = 0}$ and the amplitude of an AC steady-state voltage response (experimentally recorded) at x = 0.
The concept of reflection coefficient was introduced to the theory of electrotonus and a technique for detecting voltage signals' reflections was derived.
The impulse-response function $\sb{\rm V}$H$\sb{\rm SS-NRCAD}$(x,t)$\vert\sb{\rm x = 0}$ was shown to be relevant to the study of PSP's and PSC's integration by the soma as well as to the analysis of a plausible plastic effect of the PSP's and PSC's upon the electrical properties of a neuron of arbitrary geometry.
Finally, it is suggested that experimental assessment of adaptiveness (plasticity) of the impulse-response functions of a neuron and its parts may be important in elucidating basic physiological mechanisms for self-organization underlying learning and memory in nervous systems.
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