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Access Type

WSU Access

Date of Award

January 2019

Degree Type


Degree Name



Psychiatry and Behavioral Neurosciences

First Advisor

Paul R. Burghardt


Within the broad theoretical framework of physiological variability impacting psychology, researchers have begun to explore the role gastrointestinal microbes play in higher psychological functions. Current research on this subject is limited by small samples, inadequate control groups, or lack of evidence in human populations. However, these preliminary data, along with theoretical support, justify greater consideration for the role intestinal microbes have in modulating brain function. The body of research presented in this document was aimed at expanding our understanding of the “gut-brain-axis” in three ways. First, an in-silico analysis was conducted to evaluate how pervasive tryptophan production and degradation capability is in the bacterial kingdom. Second, a method was developed that permits a more finely resolved evaluation of fecal bacterial communities. Third, a dietary intervention was employed to better understand the relationship between diet, the gut microbiome, and resulting metabolic and psychological alterations. These three contributions are described in detail in the preceding chapters.

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