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Vocal communicators such as humans and songbirds rely on their auditory systems to learn, recognize, and encode acoustic features of communication vocalizations. Yet it remains unclear how varying behavioral, experimental, and developmental contexts impact neural coding in the songbird auditory system. In this dissertation I demonstrate that experimental and behavioral contexts relating to arousal are sufficient to alter neural excitability in a way that has implications for neural coding in the songbird auditory system. First I show that urethane, a common anesthetic used in neurophysiological studies of songbird and mammalian auditory neurons, suppresses neural excitability but does not alter spectrotemporal tuning or neural discrimination in single auditory midbrain neurons. Next, I demonstrate that neurons in the songbird primary auditory cortical region Field L are sensitive to local concentrations of norepinephrine, a neurotransmitter involved mediating changes in arousal and behavioral state. Lastly, I report the results of a developmental study that demonstrates experience-dependent changes in temporal and spectral tuning in songbird auditory cortical neurons during vocal learning. These developmental effects were found to have region and cell-type specificity, and highlight potential functional roles for dorsal and ventral auditory cortical neurons in the songbird auditory cortex. The findings reported here have important implications for future studies into the neurophysiology of vocal learning.

Thesis (Ph.D.)--Memorial University of Newfoundland, 2004. / Restricted until May 2005. Includes bibliographical references.

Two measures which indicate statistical serial dependence were evaluated. The n-dimensional Average Stored Information index (ndASI) is a measure of conditional information, which compares the entropies of higher order conditional distributions to estimate average statistical serial dependence. The generalized ranked joint interval histogram (RJIH-o) is a new nonparametric graphical analysis method. It extends the joint interval histogram by depicting longer interval sequences and can be interpereted precisely analagously to the joint interval histogram. The generalized ranked joint interval histogram correctly represents independence in a Poisson process model and statistical serial dependence in a directionally reinforced Markov model. The generalized ranked joint interval histogram correctly depicts the underlying periodic and strange attractors in a standard map model. Both measures can be used to effectively analyze interspike interval sequences from spontaneous neurophsyiological activity effectively.

Laboratory research was performed to understand leadership by attempting to link EEG baseline frequency patterns with data from the Leadership Opinion Questionnaire (LOQ) assessment survey. Research began with 293 right-handed males, 18 to 26 years-old, who completed the LOQ. Based on their scores, 61 subjects, grouped by the Ohio State Leadership Quadrants, were tested using brain-mapping technology.

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