<p>Perception arises from sensory inputs detected by peripheral organs and processed in the brain by complex neuronal circuits required for the integration of external information with internal states such as expectation and attention. Stimulus discrimination requires activation of primary sensory areas in the brain, but expectation is traditionally associated with the activation of higher-order brain areas. Sensory information obtained by tactile organs is represented along the primary areas that comprise the trigeminal thalamocortical pathway. In anesthetized animals, neuronal activity in the somatosensory system has been extensively described over the past century. However, it is still unclear how the different thalamocortical structures contribute to active tactile discrimination and represent relevant features of the stimulus. It is also unknown whether expectation modulates tactile representations in these regions. In this dissertation, I investigated neuronal ensemble activity recorded from freely behaving rats performing a whisker-based tactile discrimination t-+ask. Multielectrode arrays were chronically implanted to record simultaneously from the main stages of the trigeminal thalamocortical pathways involved in whisking: the primary somatosensory cortex (S1), the ventral posterior medial nucleus of the thalamus (VPM), the posterior medial complex (POm) and the zona incerta (ZI). In Chapter 1 I describe the behavior of rats performing the tactile discrimination task, which requires animals to associate two different tactile stimuli with two corresponding choices of spatial trajectory in order for reward to be delivered. I found that both cortical and thalamic neurons are dynamically engaged during execution of the task. The data reveal a very complex mosaic of responses comprising single or multiple periods of inhibition and excitation. Thalamocortical activity was modulated during whisker stimulation as well as after stimulus removal, up until reward delivery. To investigate whether reward expectation plays a role in tactile processing at early processing stages, I also recorded neuronal activity from rats performing a freely-rewarded version of the tactile discrimination task. Comparing data from regularly-rewarded and freely-rewarded sessions, I show in chapter 2 that the activity of single neurons in the primary somatosensory thalamocortical loop is strongly modulated by reward expectation. Stimulus-related information coded by primary thalamocortical neurons is high when a correct association between stimulus and response is crucial for reward, but decreases significantly when the association is irrelevant. These results indicate that tactile processing in primary somatosensory areas of the thalamus and cerebral cortex is directly affected by reward expectation.</p> / Dissertation

<p>The role of cardiac tissue structure in both normal and abnormal impulse conduction has been extensively studied by researchers in cardiac electrophysiology. However, much is left unknown on how specific micro- and macroscopic structural features affect conduction and conduction block. Progress in this field is constrained by the inability to simultaneously assess intramural cardiac structure and function, as well as the intrinsic complexity and variability of intact tissue preparations. Cultured monolayers of cardiac cells, on the other hand, present a well-controlled in vitro model system that provides the necessary structural and functional simplifications to enable well-defined studies of electrical phenomena. In this thesis, I developed a novel, reproducible cell culture system that accurately replicates the realistic microstructure of cardiac tissues. This system was then applied to systematically explore the influence of natural structure (e.g. tissue boundaries, expansions, local fiber directions) on normal and arrhythmogenic electrical conduction.</p><p>Specifically, soft lithography techniques were used to design cell cultures based on microscopic DTMRI (diffusion tensor magnetic resonance imaging) measurements of fiber directions in murine ventricles. Protein micropatterns comprised of mosaics of square pixels with angled lines that followed in-plane cardiac fiber directions were created to control the adhesion and alignment of cardiac cells on a two-dimensional substrate. The high accuracy of cell alignment in the resulting micropatterned monolayers relative to the original DTMRI-measured fiber directions was validated using immunofluorescence and image processing techniques.</p><p>Using this novel model system, I first examined how specific structural features of murine ventricles influence basic electrical conduction. (1) Realistic ventricular tissue boundaries, either alone or with (2) microscopic fiber directions were micropatterned to distinguish their individual functional roles in action potential propagation. By optically mapping membrane potentials and applying low-rate pacing from multiple sites in culture, I found that ventricular tissue boundaries and fiber directions each shaped unique spatial patterns of impulse propagation and additively increased the spatial dispersion of conduction velocity.</p><p>To elucidate the roles that natural tissue structure play in arrhythmogenesis, I applied rapid-rate pacing from multiple sites in culture in an attempt to induce unidirectional conduction block remote from the pacing site--a precursor to reentry. The incidence of remote block was found to be highly dependent on the direction of wave propagation relative to the underlying tissue structure, and with a susceptibility that was synergistically increased by both realistic tissue boundaries and fiber directions. Furthermore, all instances of remote block in these micropatterned cultures occurred at the anterior and posterior junctions of the septum and right ventricular free wall. At these sites, rapid excitation yielded more abrupt conduction slowing and promoted wavefront-waveback interactions that ultimately evolved into transmural lines of conduction block. The location and shape of these lines of block was found to strongly correlate with the spatial distribution of the electrotonic source-load mismatches introduced by ventricular structures, such as tissue expansions and sharp turns in fiber direction.</p><p>In summary, the overall objective of the work described in this thesis was to reveal the distinct influences of realistic cardiac tissue structure on action potential conduction and conduction block by engineering neonatal rat cardiomyocyte monolayers that reproducibly replicated the anatomical details of murine ventricular cross-sections. In the future, this novel model system is expected to further our understanding of structure-function relationships in normal and structurally diseased hearts, and possibly enable the development of novel gene, cell, and ablation therapies for cardiac arrhythmias.</p> / Dissertation

Thesis (M.A.)--York University, 1998. Graduate Programme in Psychology. / Typescript. Includes bibliographical references (leaves 66-97). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL:http://wwwlib.umi.com/cr/yorku/fullcit?pMQ27382.

Thesis (Ph.D.)--University of Delaware, 2009. / Principal faculty advisor: Robert F. Simons, Dept. of Psychology. Includes bibliographical references.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 100-110). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 100-110). Also available on the Internet.

Thesis (Ph. D.)--University of Hong Kong, 2002. / Includes bibliographical references.

<p>The ability to monitor, learn from, and respond to social information is essential for many highly social animals, including humans. Deficits to this capacity are associated with numerous psychopathologies, including autism spectrum disorders, social anxiety disorder, and schizophrenia. To understand the neural mechanisms supporting social information seeking behavior requires understanding this behavior in its natural context, and presenting animals with species-appropriate stimuli that will elicit the behavior in the laboratory. In this dissertation, I describe a novel behavioral paradigm I developed for investigating social information seeking behavior in rhesus macaques in a laboratory setting, with the use of naturalistic videos of freely-behaving conspecifics as stimuli. I recorded neural activity in the orbitofrontal and lateral prefrontal cortex of monkeys as they engaged in this task, and found evidence for a rich but sparse representation of natural behaviors in both areas, particularly in the orbitofrontal cortex. This sparse encoding of conspecifics' behaviors represents the raw material for social information foraging decisions.</p> / Dissertation

No description available.

published_or_final_version / abstract / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy