Date of Award

Summer 1969

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Biomedical Engineering

Abstract

The purpose of most studies of the evoked response has been to research one or more of the following or related topics: a) the nature of the neuronal conduction pathways involved, b) the site of origin of the response, c) the cortical projection areas of peripheral sensors, d) the degree to which scalp responses reflect responses on the cortical surface, e) the amplitude distribution over the scalp, f) the extent to which variations in stimulus parameters and sites affect response configuration, g) or, more recently, to determine the accuracy with which evoked responses may be used to assess neurological disorders. A large number of investigator's in this area have suggested or inferred that "spread", "passive extension", "field effects", or "volume conduction", by obscuring the true character of underlying phenomena, has made, difficult a definitive interpretation of much evoked response data. (Abraham and Ajmone-Marsan l958; Cobb and Sears 1960; Geisler 1960; Goff, Rosner, and Allison 1962; Kelly, Goldring, and O'Leary 1965; Kooi and Bagchi 1964a). The purpose of this study, then was to determine the relative contribution of field effects to evoked potentials that might be expected in a passive conducting medium. Of major consideration was the formulation of a mathematical model, based on known tissue conductivities and the approximate geometry of the head, from which suitable comparative theoretical data could be derived. Of special consideration was the development of a mathematical representation of a current source infinitely variable in orientation (polarity vector), magnitude, and output waveform configuration.

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