Synaptic plasticity reflects the capacity of synapses to undergo changes in synaptic strength and connectivity, and is highly regulated by age and sensory experience. This thesis focuses on the characterization of synaptic plasticity in the primary auditory cortex (A1) of rats throughout development and following sensory deprivation. Initial experiments revealed an age-dependent decline in plasticity, as indicated by reductions in long-term potentiation (LTP). The enhanced plasticity of juvenile rats appeared to be mediated by NR2B subunits of the N-methyl-d-aspartate receptor (NMDAR), as NR2B antagonist application reduced LTP to adult-like levels in juveniles, yet had no effect in adults. The importance of sensory experience in mediating plasticity was revealed in experiments using white noise exposure, which is a sensory deprivation technique known to arrest cortical development in A1. Notably, adult rats reared in continuous white noise maintained more juvenile-like levels of LTP, which normalized upon subsequent exposure to an unaltered acoustic environment. The white noise-induced LTP enhancements also appeared to be mediated by NR2B subunits, as NR2B antagonists reversed these LTP enhancements in white noise-reared rats. Given the strong influence that sensory experience exerts on plasticity, additional experiments examined the effect of shorter episodes of white noise exposure on LTP in adult rats. Exposure to white noise during early postnatal life appeared to “prime” A1 for subsequent exposure in adulthood, resulting in enhanced LTP. The necessity of early-life exposure was evident, as repeated episodes of white noise in adulthood did not enhance plasticity. In older rats that typically no longer express LTP in A1, pharmacological methods to enhance plasticity were explored. Moderate LTP was observed in older rats with cortical zinc application, which may act through its antagonism of NR2A subunits of the NMDAR. Additionally, current source density and cortical silencing analyses were conducted to characterize the distinct peaks of field postsynaptic potentials recorded in A1, with the earlier and later peaks likely representing thalamocortical and intracortical synapses, respectively. Together, this thesis emphasizes the critical role of sensory experience in determining levels of cortical plasticity, and demonstrates strategies to enhance plasticity in the mature auditory cortex. / Thesis (Ph.D, Neuroscience Studies) -- Queen's University, 2011-01-11 14:53:57.677

Music depends on the perception and production of complex temporal patterns, or rhythms, as a vital part of its power to communicate. These experiments investigated the neuroanatomical substrate of rhythm perception and production in patients with focal cerebral lesions, and in neuroimaging studies with normals. The hypotheses focused on the role of the primary and secondary auditory cortex, as well as the cerebellum and other motor-related areas. / Experiment I. To estimate the extent of removals in the region of auditory cortex in neurosurgical patients, a 3D probabilistic map of Heschl's gyrus (HG) was developed from magnetic resonance imaging (NW scans of normals. The map was coregistered with patent MRIs, revealing that most removals involved only anterior secondary auditory cortical regions, with relatively little encroachment onto primary auditory cortex. Additionally, this experiment compared the volumes of HG between hemispheres and found a consistent L > R asymmetry in the volume of cortical white matter, which could contribute directly to the preferential left-hemisphere processing of speech. / Experiment II. Using a paradigm contrasting reproduction of auditory and visual rhythms, four groups of patients were tested: those with right or left anterior temporal-lobe removals (RT-a, LT-a) and those with similar removals which also included HG (RT-A, LT-A). RT-A patients were impaired on auditory but not visual rhythms, particularly when accurate reproduction of stimulus durations was required. In contrast, LT-a, RT-a and LT-a patients were not impaired. These results demonstrated a role for the right anterior secondary auditory cortical regions in the retention of auditory temporal information. / Experiment III. The rhythm reproduction paradigm was adapted for a positron emission tomography (PET) activation study in normals. These data confirmed the participation of secondary auditory regions in the retention of auditory temporal information. They also demonstrated a supra-modal contribution of the lateral cerebellar cortices, vermis and basal ganglia to the task, pointing to a distributed system of neural structures involved in the production of a timed motor response from external stimuli. / The results are discussed in relation to possible interhemispheric differences in auditory temporal processing as well as the role of the cerebellum in motor and perceptual timing.

Attention-deficit/hyperactivity disorder (ADHD) is a developmental disorder characterized by increased hyperactivity, impulsivity, and inattention. Some theories propose that ADHD is caused by a deficit in inhibitory control, interacting with other executive functions (e.g., emotional control) to lead to behavioural dysfunction. Furthermore, certain brain regions have been found to be involved in executive functions, and several studies have examined the neural correlates of ADHD at broad-based levels. Increased interest has been placed on the Anterior Cingulate Cortex (ACC), which is known to play a role in attention and other complex cognitive processes. Thus, to further clarify the nature of the behavioural and cognitive deficits observed in ADHD, and to elucidate potential relationships between these difficulties and their neural substrates with more specificity, volumetric analyses of the ACC were conducted. For this purpose, 10 children with ADHD and 10 matched controls underwent magnetic resonance imaging and neuropsychological assessment. Manual tracing of ACC subregions was conducted using ANALYZE 9.0 (Mayo Clinic), followed by between-group statistical comparisons. Correlation analyses were used to investigate whether ACC subregions were associated with performance on executive functions tasks. It was hypothesized that there would be significant volumetric groups differences between the two groups, and that subregions would have a differential relationship with executive function performance. Results indicated the ADHD group has marginally larger right dorsal ACC volumes relative to controls. Further, between the two groups, brain-behaviour relationships were different. These results provide support for the hypothesis of a delay in neuronal maturation of the ACC in children with ADHD from Spain. / Graduate

No description available.

The mammalian visual cortex is believed to be parcellated into functional radial units called modules, which are composed of neurons with similar physiological properties. The first demonstration of modularity was provided in 1957 by Mountcastle in the somatosensory cortex, and has since been demonstrated in the visual cortex, where neurons within a vertical unit of the visual cortex process information about the same portion of the visual field. / A new approach has been proposed for identifying functionally similar neurons by examining their molecular characteristics. Indeed, the arrangement of neurons into functional arrays might be reflected by the presence of specific molecules (e.g Cat-301 patches, cytochrome oxidase blobs). / In this experiment, immunohistochemistry was used to examine the tangential and radial distribution and development of a subset of pyramidal neurons in the kitten and adult cat visual cortex using the monoclonal antibody SMI-32, that recognizes the non-phosphorylated form of neurofilament H. It was found that the neurons recognized by this antibody were grouped into clusters, forming regularly spaced patches in the infragranular and supragranular layers. These anatomical findings support the notion of an intrinsic columnar organization.

Thesis (Ph. D. in Neuroscience)--Vanderbilt University, May 2008. / Title from title screen. Includes bibliographical references.

Thesis (Ph.D.)--University of Wollongong, 2004. / Typescript. Includes bibliographical references: leaf 130-154.

Thesis (Ph.D.)--Drexel University, 2008. / Includes abstract and vita. Includes bibliographical references (leaves 95-101).

Proefschrift Universiteit van Amsterdam. / Met lit.opg. en samenvatting in het Nederlands.

Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xiv, 82 p.; also includes graphics. Includes bibliographical references (p. 80-82). Available online via OhioLINK's ETD Center