Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

Biomedical Engineering

First Advisor's Name

Ranu Jung

First Advisor's Committee Title

Committee chair

Second Advisor's Name

James Abbas

Second Advisor's Committee Title

committee member

Third Advisor's Name

Jorge Riera

Third Advisor's Committee Title

committee member

Fourth Advisor's Name

Wei-Chiang Lin

Fourth Advisor's Committee Title

committee member

Fifth Advisor's Name

Jacob McPherson

Fifth Advisor's Committee Title

committee member

Sixth Advisor's Name

Wensong Wu

Sixth Advisor's Committee Title

committee member

Keywords

microchannel, electrode, peripheral, nerve, bi-directional, mixed nerve, regenerative, efferent, afferent

Date of Defense

11-14-2019

Abstract

Microchannel electrodes have emerged in recent years as promising interfaces for recording signals in peripheral nerves. Unlike many technologies, microchannels maintain stable long-term connections and can record activity in individual or small groups of axons. Unfortunately, a traditional symmetrical mid-channel electrode configuration, designed to reduce noise artifacts, prevents microchannels from being used to distinguish between signals traveling in opposite directions. This is a profound limitation given that most nerves contain a mix of efferent and afferent axons and microchannels were initially conceived and later used as the basic building block in arrays designed to record bi-directional neural traffic in regenerated nerve fibers.

Off-center, or “offset”, recording sites have been predicted to record larger signals than mid-channel locations. Unlike the mid-channel configuration, offset electrode asymmetry suggests it has the capacity to differentiate between efferent and afferent neural activity. Despite these apparent advantages, a theoretical basis for signal enhancement at offset locations has not been identified and, to our knowledge, no efforts to leverage offset electrodes for signal enhancement or discrimination in microchannels have been undertaken.

This work provides a theoretical basis to explain signal enhancement at offset electrodes. The theory is used to explore offset electrode configurations that maximize signal amplitudes and enhance differences between signals traveling in opposite directions. Neural recordings are used to validate theoretical predictions and to explore novel reference configurations that seek to minimize noise artifacts. Key shape differences between signals recorded for action potentials traveling in opposite directions are characterized and exploited to further enhance signal discrimination at offset electrodes, as well as to reduce the rate of overlapping spikes in more complex neural recording scenarios, including compound action potentials. Overall, this work introduces the offset electrode configuration as a new paradigm for recording signals in peripheral nerves and provides a foundation for the development of future devices with enhanced performance and signal discrimination capabilities.Off-center, or “offset”, recording sites have been predicted to record larger signals than mid-channel locations. Unlike mid-channel electrodes, offset electrode asymmetry suggests they have the capacity to differentiate between efferent and afferent neural activity. Despite these apparent advantages, the theoretical underpinnings for signal enhancement at offset locations has not been identified and, to our knowledge, no efforts have been made to leverage offset electrodes for signal enhancement or discrimination in microchannels.

This work provides a theoretical basis to explain signal enhancement at offset electrodes. The theory is used to explore and identify offset electrode configurations that maximize signal amplitudes and seek to enhance differences between signals traveling in opposite direction. Neural recordings in microchannels containing optimally-positioned offset electrodes are used to validate theoretical predictions and to explore novel reference configurations for minimizing noise artifacts. Shape differences between signals recorded at mid-channel and offset locations are characterized and exploited to further enhance signal discrimination at offset electrodes for single units and reduce the rate of overlapping spikes in more complex multi-unit spike trains as well as the compound action potential. Overall, this work demonstrates a new paradigm for neural recording in microchannels that provides a foundation for the development of future devices with enhanced performance and signal discrimination capabilities.

Identifier

FIDC008853

Available for download on Sunday, December 12, 2021

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