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Plasticity of synapses is not static across the lifespan. As the brain matures and ages, the ability of neurons to undergo structural and functional change becomes more limited. Further, there are a number of modulatory factors that influence the expression of synaptic plasticity. Here, three approaches were taken to examine and manipulate plasticity in the auditory thalamocortical system of rats. Using an in vivo preparation, long-term potentiation (LTP) and paired pulse (PP) responses were used as measures of long- and short-term plasticity, respectively. First, the effect of intracortical zinc application in the primary auditory cortex (A1) on LTP was examined. Following theta burst stimulation (TBS) of the medial geniculate nucleus (MGN), juvenile and middle-age rats, but not young adults, showed greater levels of LTP with zinc application relative to age-matched control animals. Next, PP responses were examined between rats reared in unaltered acoustic conditions and those reared in continuous white noise (WN) from postnatal day (PD) 5 to PD 50-60 (i.e., subjected to patterned sound deprivation). Rats reared in WN demonstrated less PP depression relative to controls, indicating that WN rearing alters short-term thalamocortical synaptic responses. Furthermore, control males showed no change in PP response following LTP induction, indicating a postsynaptic locus of LTP, whereas increased PP depression following LTP induction was seen in WN animals, suggestive of a presynaptic involvement in LTP. Finally, differences in plasticity between male and female rats were investigated, and the result of early WN exposure on both sexes was examined. Males and females did not show consistent differences in LTP expression; however WN exposure appeared to affect LTP of females less than their male counterparts. PP responses were then compared between WN-reared males and females, and no difference was found. This indicates that short-term plastic properties of auditory thalamocortical synapses between the sexes do not differ, even though plasticity on a longer time scale following sensory deprivation does indicate some difference. Together, the experiments summarized here identify some of the important factors that contribute to the regulation of short- and long-term synaptic plasticity in the central auditory system of the mammalian brain. / Thesis (Master, Neuroscience Studies) -- Queen's University, 2012-10-30 16:01:28.796

Theories of pitch perception, and the related literature, are reviewed, with special reference to the residue pitch of tonal complexes. A distinction is drawn between spectral-pattern theories, which propose that pitch is derived from independent internal estimates of component frequency, and periodicity theories, which propose that the pitch of tonal complexes may be derived from a residual periodicity resulting from an incomplete auditory frequency analysis. The Spectral-pattern models described by Goldstein (1973) and Wightman (1973b) are discussed in detail; computer simulation procedures, allowing the prediction of a probability density function for the estimated fundamental frequency of a tonal complex, are described for each. Contrasting predictions concerning the relation between component frequency discrimination and fundamental frequency discrimination for harmonic complexes are developed for the spectral-pattern and periodicity theories. Component frequency and fundamental frequency discrimination by human observers was measured, under a variety of conditions, for a complex containing the 4th and 5th harmonics of 200 Hz. For a comparison of the pitches of two such complexes of slightly different frequency, the relative fundamental frequency difference limen was no larger, and generally smaller, than the smaller relative component frequency difference limen. Discrimination performance was interpreted in terms of a modified version of Goldstein's (1973) spectral-pattern theory, in which an internal noise limits discrimination between signals with non-coincident components. Further experiments investigated the identification of fundamental frequency by human observers as a function of the variability of internal estimates of component frequency as estimated from the discrimination experiments. The results of these experiments were consistent with the predictions of the spectral-pattern theories. Component and fundamental frequency discrimination was also considered with respect to temporal and spatial theories of frequency discrimination. The results of the discrimination studies were consistent with a modified Energy Detection model, where discrimination is ultimately limited by an internal noise.

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Digitized by Kansas Correctional Industries

Digitized by Kansas Correctional Industries

acase@tulane.edu / The following dissertation project included three behavioral experiments indexing spatial attention in the auditory modality. Each experiment varied in terms of predictable stimulus features on the task, and demonstrated differential engagement of spatial attention depending on if stimulus location or identity was predictable on any given trial. Experiment 1 involved no predictable features. Experiment 2 involved predictable sound identity presented from unpredictable locations. Experiment 3 presented sounds with unpredictable identity from a predictable location. All experiments involved judging the identity of the sound in a two-choice reaction time style task. All three experiments also included memory load, loading memory with sound identities or locations on a given block. A dual-task design was employed in order to investigate Reaction Time and Accuracy effects related to maintaining features in memory that were also present during the selective attention task. Experiments employed conditions with variable levels of overlap across features in memory and attention; investigating overlap at the level of feature-type (i.e. maintaining one color in memory while attending to another) and at the level of specific feature (i.e. attending to the color blue while it also happens to be retained in memory). Results demonstrated improved reaction time and accuracy for expected sounds and sounds from expected locations. Additionally, memory load showed interference on the basis of load-type (reflective of specialized load effects), and showed slower reaction times for stimuli that contained features which overlapped with features in memory (primarily for unexpected stimuli). These results contradicted findings in the visual modality that have reported faster reaction times for stimuli that match with features stored in memory. This difference in findings is most likely driven by differences between auditory and visual attention, the impact of unpredictability on overlap, or both. / 1 / Maxwell Anderson

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Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves 284-291).