The amygdala, in particular its basolateral part (BLA), plays a critical role in binding affective qualities to otherwise neutral stimuli, and in eliciting emotional behaviors. Plasticity of inputs to BLA projection neurons involved in emotional memory has been extensively studied. However, how BLA neurons collectively process sensory information to encode and stabilize emotional memories is unknown. Precise coordination of BLA network activities seems critical. Specifically, timed integration of salient stimuli, and synchrony with hippocampal theta oscillations appear to be important. Recent reports suggest that GABAergic neurons may be instrumental in shaping ensemble activity in the BLA. Studies of neocortex and hippocampus showed that diverse GABAergic interneuron types play highly specific roles in coordinating network operations. The presence of similar interneuron populations in the BLA suggests comparable mechanism may govern its activities. However, GABAergic cell types and their functions have not been characterized.

Neuregulin 1 (NRG1) is a growth factor implicated in neurodevelopment and postnatal maintenance of synaptic circuits. Its gene has been associated with schizophrenia, and the expression of the type I isoform (NRG1tyI) is increased in patients’ brains. Earlier behavioural phenotyping of mice over-expressing NRG1tyI revealed impairment in hippocampus-dependent spatial working memory. This present work investigates the effects of increased NRG1tyI expression on hippocampal network functioning in these mice. Fast network oscillations, specifically at gamma frequencies, were studied in CA3 hippocampal slices in a carbachol model using cellular and extracellular microelectrode recording techniques. The peak frequency of field potential oscillations was significantly reduced in slices from NRG1tyI mice compared to wild-type littermates. In addition, NRG1tyI mouse slices were more prone to develop epileptiform activity. During rhythmic activity, the balance of phasic excitation and inhibition was significantly altered in principal cells of NRG1tyI mice. Inhibitory synaptic input was more sustained, while excitatory synaptic currents were kinetically unchanged but larger and more variable in amplitude. Together, these data suggest altered functioning of the GABAergic inhibitory circuits that generate and maintain gamma oscillations. Because parvalbumin-expressing (PV+) interneurons are a major target of NRG1 signalling, the inhibition from PV+ interneurons to pyramidal cells was examined next. Channelrhodopsin-2-mediated photostimulation of PV+ cell axons failed to show changes in GABAergic inhibition of CA3 pyramidal cells in NRG1tyI mice. However, synaptic miniature glutamatergic neurotransmission was reduced in identified PV+ basket cells (BCs) and axo-axonic cells (AACs) but not in pyramidal cells. The change was expressed postsynaptically, affecting NMDA receptor- but not AMPA receptor-mediated currents. The data suggest that NRG1tyI over-expression results in alterations in PV+ interneuron types, particularly at the glutamatergic synapses that excite these cells. These changes and the altered gamma oscillations are already evident in late adolescence — before the age at which cognitive deficits are detectable.

This thesis investigation concerns the optical and nonlinear electrical properties of n-InSb. Two specific areas have been studied. First is the magneto-optical study of magneto-donors, and second is the nonlinear dynamic study of nonlinear and chaotic oscillations in InSb. The magneto-optical study of InSb provides a physical picture of the magneto-donor levels, which has an important impact on the physical model of nonlinear and chaotic oscillations. Thus, the subjects discussed in this thesis connect the discipline of semiconductor physics with the field of nonlinear dynamics.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

The subthalamic nucleus (STN), which is the most common target for deep brain stimulation for Parkinson's disease, is known to be crucially involved in motor control. Recent appreciation of the potential non-motor side effects of STN deep brain stimulation, however, has led to speculation that the importance of this nucleus may also relate to processes involved in decision- making, particularly during high conflict scenarios. This thesis concerns itself with investigating the STN's role in action selection during conflict. I begin by recording local field potentials directly from the STN of Parkinson's disease patients while they perform a flanker task that has been shown to elicit theta (4-8 Hz) band activity in areas of the prefrontal cortex involved in cognitive control. I report that like the prefrontal cortex, the STN demonstrates elevated theta activity during conflict. I then test whether STN theta activity is related to that of the prefrontal cortex by recording from both sites simultaneously while patients perform a novel task that temporally separates conflict from stimulus onset or movement. This reveals that theta activity indeed becomes synchronized during conflict, with cortical oscillations driving those of the STN. Thirdly, I investigate how STN oscillations may affect firing rate dynamics by intra-operatively recording local field potentials and single unit activity from patients performing the flanker task. I report that both theta and beta (15-30 Hz) oscillations entrain STN neurons, but only during conflict. Finally, I record cortical and STN activity while a fourth group of patients performs the flanker task. This experiment confirms that cortico-STN theta synchrony is elevated during conflict and may also relate to across-trial adaptations to conflict and errors. Taken together these studies shed light on the mechanisms by which cortical structures may influence the STN during conflict and why STN deep brain stimulation may result in impulsivity.

[pt] Nesta dissertação, estudamos do ponto de vista fenomenológico, os efeitos de neutrinos estéreis para os observáveis de massas de neutrinos baseado nos dados do experimento LSND e nos resultados divulgados recentemente pela colaboração MiniBooNE. Consideramos observáveis de massa as seguintes quantidades: o parâmetro de massa cinemática cuja medida é realizada em experimentos com o decaimento beta do tritium tendo seu valor atual fornecido pelos experimentos Mainz e Troitsk; a massa efetiva de Majorana, que é uma quantidade que pode ser obtida em experimentos com o duplo decaimento beta sem neutrinos; finalmente, a soma de massas dos neutrinos, a qual é vinculada por dados cosmológicos. Nossa análise é realizada considerando os possíveis ordenamentos de massas para o caso em que temos dois neutrinos estéreis além dos três neutrinos ativos usuais, cuja adição é necessária para explicar os resultados de LSND e MiniBooNE ao mesmo tempo. Neste cenário, temos oito possíveis ordenamentos de massas, os quais dividimos em três grupos. No primeiro grupo, temos que os dois neutrinos estéreis são mais pesados que os três neutrinos ativos. No segundo grupo, os dois neutrinos estéreis são mais leves que os três neutrinos ativos. Cada um destes dois grupos tem possibilidades que dependem do ordenamento de massas dos neutrinos ativos que pode ser normal ou invertido. No terceiro e último grupo temos que um neutrino estéril é mais leve e o outro mais pesado que os três neutrinos ativos. Neste grupo, existem quatro possibilidades de ordenamento associada ao posicionamento dos neutrinos estéreis e ao ordenamento dos neutrinos do setor ativo. Investigamos os observáveis de massas em cada um destes cenários. / [en] In this dissertation we study, from the phenomenological point of view, the effects of sterile neutrinos for the observables related to neutrino masses based on the data of the LSND experiment and on the results releasedrecently by the MiniBooNE collaboration. We consider the following mass related obsevables: the kinematic mass parameter which is obtained in tritium beta decay experiments whose current value is provided by Mainzand Troitsk experiments; the Majorana effective mass, it is a quantity that can be obtained in neutrinoless double beta decay experiments. In additionto these quantities, we also consider the sum of neutrinos masses, which isconstrained by cosmological data. Our analysis is performed by considering the possible mass orderings for the cases where we have two sterile neutrinosbeyond the three standard active neutrinos, whose addition is necessary to explain the results of LSND andMiniBooNE simultaneously. In this scenariot here are eight possible mass orderings, which are divided into three groups.In the first group we have two sterile neutrinos which are heavier thanthe three active neutrinos. In the second group the two sterile neutrinosare lighter than the three active neutrinos. Each of these two groups canbe further divided into 2 subgroups depending on the mass ordering ofthe active neutrinos that can be normal or inverted. In the third and lastgroup we have one sterile neutrino lighter and the other heavier than thethree active neutrinos. In this group there are four possibilities of ordering depending on the positioning of the sterile neutrinos with respect to theactive ones and on the mass ordering of the active states. We investigate systematically the masses observable in each of these scenarios.

No description available.

>Magister Scientiae - MSc / Future radio surveys as the Square Kilometer Array (SKA) and its precursor, the "Meer" Karoo Array Telescope (MeerKAT), will map the Neutral Hydrogen (HI) in large areas of the sky using the intensity mapping (IM). HI IM is currently one of the most promising ways of accessing the Large-Scale Structure of the Universe. The distribution of matter in the Universe not only encodes its composition but also how it evolves and its initial conditions. An effect on the matter distribution that will be detected by the SKA on the post re-ionization Universe are the Baryonic Acoustic Oscillations (BAO). While it has been shown that in single dish mode the SKA can measure the BAO peak in the radial 21cm power spectrum at low redshifts, this possibility has not yet been studied in detail for the MeerKAT. In this thesis we construct a set of full sky simulations to test how well MeerKAT will be able to extract the BAO wiggles along the line of sight. These simulations are done for the frequencies corresponding to MeerKAT L-band. The maps combine the cosmological HI signal, systematic noise, cosmological foregrounds and the instrumental telescope beam. A model-independent estimator is used to extract the BAO wiggles by subtracting a smooth polynomial component from the 21cm radial power spectrum. We test with simulations if this estimator is biased and the signal to noise of the extraction. We conclude that we are able to remove contaminants and recover the cosmological HI signal while not risking the recovery of the BAO signal. We investigate the effects of varying the sky area and the observational hours on the signal to noise ratio for the BAO wiggles. We found that for a HI IM experiment using MeerKAT, the optimal sky area to detect the BAO along the line of sight is 50% of the sky. With a signal-to-noise ratio of 3.37. This can be achieved with 2000 hours of exposure time

Thesis (Ph.D.(Civil Engineering))--University of the Witwatersrand, Faculty of Engineering, 1966.

Nesta tese, apresentamos estudos de magnetotransporte em poços quânticos duplos (DQWs) a campos magnéticos de baixo e sob a aplicação de um campo elétrico externo (potencial de porta). Medidas de magnetorresistência foram realizadas tanto no regime linear quanto no regime não linear. Relatamos a observação de oscilações magnéticas de inter-sub-banda (MIS) pela primeira vez. Estas oscilações MIS já foram estudadas em poços quânticos simples (QWs) com duas sub-bandas ocupadas; um DQW´e o sistema mais apropriado para o estudo das oscilações MIS. As oscilações MIS são atribuídas ao espalhamento inter-sub-banda, e a intensidade delas depende da largura da barreira (relacionada ao gap de energia entre as duas sub-bandas ocupadas, SAS). O estudo das oscilações MIS é uma ferramenta importante para poder acessar ao tempo de vida quântico dos elétrons a temperaturas onde as oscilações Shubnikov-de Haas (SdH) já não são observadas. Em nossas amostras, as oscilações MIS persistem até 25 K. Explicamos estes resultados num modelo teórico considerando um potencial de espalhamento de curto alcance com uma contribuição significativa do tempo de espalhamento elástico dos elétrons e uma contribuição do espalhamento elétron-elétron (e-e) com o aumento da temperatura. A aplicação de um campo elétrico externo (correntes dc) modifica fortemente as oscilações MIS. Descrevemos este efeito não linear causado pelo campo elétrico dc com uma função de distribuição oscilatória. Considerando o aquecimento dos elétrons pelo campo elétrico, é extraído o tempo de espalhamento inelástico. Para correntes dc grandes são encontradas discrepâncias entre o experimento e a teoria. Finalmente, consideramos medidas de magnetotransporte como função de potenciais de porta (porta na superficie) levando ao desbalance do DQW. Encontramos que as contribuições clássica e quântica são necessárias para a descrição teórica da magnetorresistência. Descrevemos as contribuições da magnetorresistência em termos das taxas de espalhamento inter e intra sub-banda utilizando uma função gaussiana como função da correlação do potencial. / In this thesis we present studies of magnetotransport in double quantum wells (DQWs) in low magnetic fields and under application of an external electric field (gate potential). Measurements of magnetoresistance have been carried out in both linear and non-linear regime. We report on the observation of magneto-intersubband (MIS) oscillations for the first time. These MIS oscillations have been studied already in quantum wells (QWs) with two occupied subbands, DQW is the most convenient system for studies of MIS oscillations. They are attributed to intersubband scattering and the strength of MIS oscillations depends on the barrier width (´delta´SAS). Analysis of MIS oscillations is an important tool to access quantum lifetime of electrons at high temperatures where Shubnikov-de Haas (SdH) oscillations are already absent. For our samples, MIS oscillations still exist up to 25 K. We explain these results in a theoretical model considering short-range scattering potential with a significant contribution of el´astic scattering time of electrons and a contribution of electron-electron (e-e) scattering if one increases temperature. Application of an external electric field (here a dc currents) strongly modifies the MIS oscillations. We describe this non-linear effect caused by a dc electric field with nonequilibrium part of the electron distribution function. Including the heating of electrons by the electric field, we are able to extract inelastic scattering time. For a strong dc current, a discrepancy between experiment and theory is found. Finally, we consider gate-dependent (top gate) magnetotransport measurements and drive de DQWs out of balance. We find that both cl´assical and quantum contributions are necessary for theoretical description of the magnetoresistance. We express both contributions in terms of inter and intrasubband scattering rates using a gaussian function as correlation function of the potential.