3-D ANALYSIS OF AUDITORY BRAINSTEM RESPONSE COMPONENTS

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The goal of this research is to establish the surface potential patterns of elements of the Auditory Brainstem Response (ABR) in terms of the different axonal shapes and positions of neurons in the brainstem auditory system. The 3-Dimensional Lissajous Trajectory (3-CLT) is the resulting waveform when recordings from three orthogonally-placed electrodes are simulatneously plotted in three-dimensional voltage space. The 3-CLT of the ABR is known to produce planar curves whose shape and position are determined (at least in part) by the zonal portions of activated brainstem neurons. This research will examine the 3-CLT consequences of different axonal shapes and positions by placing a frog's nerve within a cat's skull filled with Ringer's solution, at the location of known brainstem axons. The success of this biological modelling will be measured by comparison with 3-CLT recordings from anesthetized cats, especially those in which only the VIIIth nerve is active. If successful, the research can be extended to study the likely contributions to human ABR recordings of specific neurons in the auditory brainstem system. Such an ability will provide more information as to how to interpret pathological changes in the ABR, a common clinical tool. Non-standard electrode placements to maximize the detection of abnormalities in specific neurons could be planned on the basis of this research. In addition, the effects of pre-amplifier filters, signal-to-noise ratio, and stimulus rate and intensity will be studied. Simpler methods for analyzing the 3-CLT will be evaluated using vector-time plots, and etection of straight line segments by analysis of the first derivative of the recorded waveforms.