Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item RAPID ADAPTIVE PLASTICITY IN AUDITORY CORTEX(2010) Atiani, Serin; Shamma, Shihab A; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Navigating the acoustic environment entails actively listening for different sound sources, extracting signal from a background of noise, identifying the salient features of a signal and determining what parts of it are relevant. Humans and animals in natural environments perform such acoustic tasks routinely, and have to adapt to changes in the environment and features of the acoustic signals surrounding them in real time. Rapid plasticity has been reported to be a possible mechanism underling the ability to perform these tasks. Previous studies report that neurons in primary auditory cortex (A1) undergo changes in spectro-temporal tuning that enhance the discriminability between different sound classes, modulating their tuning to enhance the task relevant feature. This thesis investigates rapid task related plasticity in two distinct directions; first I investigate the effect of manipulating task difficulty on this type of plasticity. Second I expand the investigation of rapid plasticity into higher order auditory areas. With increasing task difficulty, A1 neurons' response is altered to increasingly suppress the representation of the noise while enhancing the representation of the signal. Comparing adaptive plasticity in secondary auditory cortex (PEG) to A1, PEG neurons further enhance the discriminability of the sound classes by an even greater enhancement of the target response. Taken together these results indicate that adaptive neural plasticity is a plausible mechanism that underlies the performance of novel auditory behaviors in real time, and provide insights into the development of behaviorally significant representation of sound in auditory cortex.Item Ocular Barriers to Transscleral Drug Delivery and Pharmacokinetics of an Episcleral Implant(2006-06-02) Lee, Susan Shu-Hsun; Wang, Nam Sun; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The eye presents several anatomic and physiologic barriers that pose a major challenge for targeted drug delivery. The primary causes of vision impairment and blindness result from posterior segment diseases and corneal diseases[1]. To tackle these sight-threatening diseases, a number of therapeutic methods have been investigated, ranging from topical eye drops to injections and implants. Thus, the development of effective delivery systems depends upon the understanding of how the ocular barriers affect the pharmacokinetics of drugs. In Part 1, investigation of the barriers to transscleral drug delivery was performed in a rabbit model, and the model demonstrated that the conjunctival lymphatic and blood vessels may be a predominant barrier to the delivery of triamcinolone acetonide to the vitreous. In Part 2, the pharmacokinetics of a cyclosporine episcleral implant for high-risk penetrating keratoplasties was also studied, and the implant was safe and effective at delivering therapeutic levels to the cornea and surrounding tissues.