Plasticity of residual cortical tissue has been identified as an important mediator of functional post-stroke recovery. After neonatal stroke the thickness of residual tissue can change, the tissue can move, and tissue can fill in the stroke core. Nevertheless, the majority of preclinical stroke research utilizes adult rats. Thus, the purpose of the present thesis was to systematically document such gross morphological changes in peri-infarct tissue after stroke in the adult rat. Morphological changes were assessed in pial strip devascularization, photothrombotic occlusion, and middle cerebral artery occlusion models of stroke using histological and magnetic resonance imaging. Decreases in cortical thickness, volume, and neural density were found to extend far beyond the stroke infarct and included the sensorimotor regions of the intact hemisphere. Movement of residual tissue towards the infarct was observed and confirmed using anatomical markers placed in intact cortical tissue at the time of stroke induction. I conclude that the extensive time-dependent morphological changes that occur in residual cortical tissue must be considered when evaluating plasticity-related cortical changes associated with post-stroke recovery of function. / ix, 162 leaves : ill. ; 28 cm

When given a choice between getting a high reward that requires climbing a high ramp or pressing a lever multiple times, versus freely obtaining a low reward, healthy rats prefer the former, while rats with lesions to the anterior cingulate cortex (ACC) prefer the latter. We developed two novel effort tasks to examine if ACC mediates other types of physical effort (weight-lifting) as well as emotional effort (courage). We replicated previous findings on a modified version of the ramp-climbing task, showing that ACC lesions impair these decisions. Lesions of ACC did not impair weight-lifting effort, even when higher levels of effort were used and training on the task was eliminated. Initially, lesions of ACC did not impair courage effort. When the task effort was subsequently increased, rats with ACC lesions showed a failure to adapt to novelty throughout testing. This research indicated that not all effort is mediated by ACC. / xii, 177 leaves : ill. ; 29 cm

Adrenalectomy (ADX) has been shown to cause selective degeneration of granule cells in the dentate gyrus (DG). This occurs due to the reduction of corticosterone (CORT) and behavioural deficits are associated with the loss of these neurons. Dentate lesions and cell loss associated with ADX have been shown to effect behaviour in a number of spatial tasks. In contras, it has been shown granule cell loss does not affect the specificity of place cells in CA3 and CA1. We used the ADX model to examine the role of DG granule cells plays in representing space using immediate early gene (IEG) activation in the principal hippocampal subfields after exploration of novel environments. Rats were allowed to free explore multiple novel environments and then the mRNA for the IEG Homer 1a (H1a) was used as a marker of neural activity. After degeneration of approximately half of the DG granule cells we found a significant increase in number of active cells in the DG, CA3 and CA1 in ADX animals. The results indicate a reduction in granule cells causes a dramatic increase in the proportion of remaining DG granule cells in response to exploration. The change in DG activation disrupts the representations in CA3 and CA1 and thereby affects behaviour. / vii, 60 leaves : ill. (some col.) ; 29 cm

During neural activity, action potentials travel down axons, generating effective charge current pulses, which are central in neuron-to-neuron communication. Consequently, said current pulses generate associated magnetic fields with amplitudes on the order of picotesla (pT) and femtotesla (fT) and durations of 10’s of ms. Magnetoencephalography (MEG) is a technique used to measure the cortical magnetic fields associated with neural activity. MEG limitations include the inability to detect signals from deeper regions of the brain, the need to house the equipment in special magnetically shielded rooms to cancel out environmental noise, and the use of superconducting magnets, requiring cryogenic temperatures, bringing opportunities for new magnetic sensors to overcome these limitations and to further advance neuroscience. An extraordinary magnetoresistance (EMR) tunable graphene magnetometer could potentially achieve this goal. Its advantages are linear response at room temperature (RT), sensitivity enhancement owing to combination of geometric and Hall effects, microscale size to place the sensor closer to the source or macroscale size for large source area, and noise and sensitivity tailoring. The magnetic sensitivity of EMR sensors is, among others, strongly dependent on the charge mobility of the sensing graphene layer. Mechanisms affecting the carrier mobility in graphene monolayers include interactions between the substrate and graphene, such as electron-phonon scattering, charge impurities, and surface roughness. The present work reviews and proposes a material set for increasing graphene mobility, thus providing a pathway towards pT and fT detection. The successful fabrication of large-size magnetic sensors employing CVD graphene is described, as well as the fabrication of trilayer magnetic sensors employing mechanical exfoliation of h-BN and graphene. The magneto-transport response of CVD graphene Hall bar and EMR magnetic sensors is compared to that obtained in equivalent trilayer devices. The sensor response characteristics are reported, and a determination is provided for key performance parameters such as current and voltage sensitivity and magnetic resolution. These parameters crucially depend on the material's intrinsic properties. The Hall cross magnetic sensor here reported has a magnetic sensitivity of ~ 600 nanotesla (nT). We find that the attained sensitivity of the devices here reported is limited by contaminants on the graphene surface, which negatively impact carrier mobility and carrier density, and by high contact resistance of ~2.7 kΩ µm at the metallic contacts. Reducing the contact resistance to < 150 Ω µm and eliminating surface contamination, as discussed in this work, paves the way towards pT and ultimately fT sensitivity using these novel magnetic sensors. Finite element modeling (FEM) is used to simulate the sensor response, which agrees with experimental data with an error of less than 3%. This enables the prediction and optimization of the magnetic sensor performance as a function of material parameters and fabrication changes. Predictive studies indicate that an EMR magnetic sensor could attain a sensitivity of 1.9 nT/√Hz employing graphene with carrier mobilities of 180,000 cm²/Vs, carrier densities of 1.3×10¹¹ cm^-2 and a device contact resistance of 150 Ω µm. This sensitivity increments to 443 pT/√Hz if the mobility is 245,000 cm²/Vs, carrier density is 1.6×10¹⁰ cm^-2, and a lower contact resistance of 30 Ω µm. Such devices could readily be deployed in wearable devices to detect biomagnetic signals originating from the human heart and skeletal muscles and for developing advanced human-machine interfaces.

Diese Arbeit befasst sich mit der automatisierten Analyse der Ausrichtungen von Neuronenfasern in Mikroskopiebildern des menschlichen Gehirns. Für eine solche Analyse wurden vom Paul-Flechsig-Institut für Hirnforschung Leipzig (PFI) Fluoreszenzbilddaten zur Verfügung gestellt. Um für diese Daten Faserausrichtungen zu ermitteln, werden drei Schritte durchgeführt: Neuronenfasern werden hervorgehoben, bzw. freigestellt, es werden Orientierungen zu diesen zugeordnet und die hierdurch ermittelten Ergebnisse werden visualisiert. Es werden für jeden dieser Schritte mehrere Verfahren der klassischen Bildverarbeitung vorgestellt und die Auswirkung verschiedener Parameter auf deren Ergebnisse untersucht. Betrachtet werden Verfahren zur Kontrasterhöhung, Gauß-Filter, auf Hessematrizen basierende Filter, Berechnung von Phasenübereinstimmung und eine Wavelet-Transformation. Alle während dieser Arbeit vorgenommenen Implementierungen stehen als Python-Skripte auf GitHub (https://github.com/saphyll/fiber-orientation) zur Verfügung.:Einleitung 1. Grundlagen 1.1 Datengrundlage 1.2 Architektur 1.3 Grundlagen der Bildverarbeitung 1.3.1 Histogramme 1.3.2 Konvolution 1.3.3 Gaußkernel 1.3.4 Hessematrix und Eigenvektoren 1.4.5 Fourier-Transformation 2. Faseranalyse in 2D 2.1 Hervorhebung von Fasern 2.1.1 Histogram Equalization 2.1.2 Gauß-Filter 2.1.3 Hessematrix-basierte Filter 2.1.4 Phase Congruency 2.1.5 Isotropic Undecimated Wavelet Transform 2.2 Analyse und Visualisierung von Faserrichtungen 2.2.1 Richtungshistogramme 2.2.2 Kacheln 2.2.3 Direkte Ergebnisbilder 3. Zusammenfassung und Ausblick / This thesis covers the automated analysis of fiber orientations in microscopic images of the human brain in regard to data provided by the Paul Flechsig Institute of Brain Research Leipzig (PFI). For the retrieval of information about fiber orientations, three steps are used: An enhancement of fiber visibility and definition, an assignment of orientations to those fibers and a visualisation of fibers and their orientations. Multiple methods from classical image processing are presented for each of these steps and are evaluated according to the available data. These methods include contrast enhancement, gaussian filters, hessian filters, calculation of phase congruency and a wavelet transformation. All implementations resulting from this thesis are available as Python scripts on GitHub (https://github.com/saphyll/fiber-orientation).:Einleitung 1. Grundlagen 1.1 Datengrundlage 1.2 Architektur 1.3 Grundlagen der Bildverarbeitung 1.3.1 Histogramme 1.3.2 Konvolution 1.3.3 Gaußkernel 1.3.4 Hessematrix und Eigenvektoren 1.4.5 Fourier-Transformation 2. Faseranalyse in 2D 2.1 Hervorhebung von Fasern 2.1.1 Histogram Equalization 2.1.2 Gauß-Filter 2.1.3 Hessematrix-basierte Filter 2.1.4 Phase Congruency 2.1.5 Isotropic Undecimated Wavelet Transform 2.2 Analyse und Visualisierung von Faserrichtungen 2.2.1 Richtungshistogramme 2.2.2 Kacheln 2.2.3 Direkte Ergebnisbilder 3. Zusammenfassung und Ausblick

Sutherland, Sparks and Lehmann (2010) proposed a new theory of memory consolidation, termed Distributed Reinstatement Theory (DRT), where the hippocampus (HPC) is needed for initial encoding but some types of memories are established in non-HPC systems through post-learning HPC activity. An evaluation of the current methodology of temporary inactivation was conducted experimentally. By permanently implanting two bilateral guide cannulae in the HPC and infusing ropivacaine cellular activity could be reduced by 97%. Rats were trained in a context-fear paradigm. Six learning episodes distributed across three days made the memory resistant to HPC inactivation while three episodes did not. Blocking post-learning HPC activity following three of six training sessions failed to reduce the rat’s memory of the fearful context. These results fail to support DRT and indicate that one or more memory systems outside the HPC can acquire context memory without HPC post-event activity. / x, 85 leaves : ill. ; 29 cm

No description available.

This study sought to determine whether the DG, CA3, and CA1 regions contain uniformly excitable populations and test the hypothesis that rapid addition of new, more excitable, granule cells in prepubescence results in a low activation probability (P1) in the DG. The immediate-early gene Homer1a was used as a neural activity marker to quantify activation in juvenile (P28) and adult (~5 mo) rats during track running. The main finding was that P1 in juveniles was substantially lower not only the DG, but also CA3 and CA1. The P1 for a DG granule cell was close to 0 in juveniles, versus 0.58 in adults. The low P1 in juveniles indicates that sparse, but non-overlapping, subpopulations participate in encoding events. Since sparse, orthogonal coding enhances a network’s ability to decorrelate input patterns (Marr, 1971; McNaughton & Morris, 1987), the findings suggest that juveniles likely possess greatly enhanced pattern separation ability. / ix, 51 leaves : ill. ; 29 cm

This dissertation explores the connections that exist between Gertrude Steins late nineteenth-century psychological studies at Harvard University, her fin-de-sicle brain research at the Johns Hopkins Medical School, and her early twentieth-century cubist writings. This study is important to neuraesthetic researchers, because it appears that Stein produced a secret series of cubist brain maps from approximately 1912 to 1935, and then published her first explicit brain map in _The Geographical History of America or the Relation of Human Nature to the Human Mind_, in 1936. The cubist brain maps that Stein produced during this period can be conceptualized as evolving, neuraesthetic writing practices that reflect her complex, scientific insights and her varied, artistic associations. One of the primary differences between Steins cubist writings and those of her literary peers is that she deploys the cubist painting strategies of Pablo Picasso, for the purpose of portraying the human central nervous system. In addition to exploring the scientific meanings of Steins multidimensional, performative and introspective cubist puns, my study examines how Stein uses color in her cubist writings, as a means of anticipating the visual effects of future scientific discoveries and connectivity maps, such as the Brainbow system, which uses the fluorescent protein from the jellyfish Aequorea Victoria to label the central nervous systems of genetically modified mice with distinguishable colors. Also, this project examines how Stein uses color words and other simple devices from the English language to illustrate the brains cellular structures, neural networks and neuroanatomical features. This studys primary aim is to explore how Steins dissociative writings function within western culture as neuraesthetic modes of masterpiece creation, brain representation and consciousness translation. Through the serial production of cubist brain maps, Stein posed important questions about the modern science of the reading brain. By developing allegorical methods of brain representation, Stein contributes to the western practice of neuroesthetics by foregrounding the role that creative writing plays in the production of imaginary, laboratory practices and imaginative, brain imaging technologies.

An initial aim of this thesis was to determine whether training of a specific executive function (updating) produces improvements in performance on trained and transfer tasks, and whether the effects are maintained over time. Neural systems underlying training and transfer effects were also investigated and one question considered is whether transfer depends on general or specific neural overlap between training and transfer tasks. An additional aim was to identify how individual differences in executive functioning are mapped to functional brain changes. In Study I, significant training-related changes in performance on the letter memory criterion task were found in both young and older adults after 5 weeks of updating training. Transfer to a 3-back test of updating was also demonstrated in the young adults. Functional Magnetic Resonance Imaging (fMRI) revealed overlapping activity in letter memory and 3-back tasks in fronto-parietal areas and striatum pre-training, and a joint training-related activity increase for the tasks in a striatal region. No transfer was observed to a task (Stroop) that engaged fronto-parietal areas, but not the striatal region and updating per se. Moreover, age-related striatal changes imposed constraints on transfer. In Study II, additional transfer tasks and a test of long-term maintenance were included. Results revealed that training-related gains in performance were maintained 18 months post-training in both young and older adults, whereas transfer effects were limited to tasks requiring updating and restricted to young participants. In Study III, analyses of brain activity and performance during n-back (1/2/3-back) were executed. This task enables manipulation of executive demand, which permits examination of how individual differences in executive functioning can be mapped to functional brain changes. Relative to a young high- performing group, capacity constraints in executive functioning were apparent between 1–2-back for the elderly participants and between 2–3-back for a young low-performing group. Capacity constraints in neural activity followed this pattern by showing a monotonically increasing response in the parietal cortex and the thalamus for young high performers, whereas activity levelled off at 1-back for elderly performers and at 2-back for young low performers. The response in the dorsal frontal cortex followed a similar pattern. Together, these findings indicate that fronto-parietal as well as sub-cortical areas are important for individual differences in executive functioning, training of updating and transfer effects.