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Cognitive Event-Related Potential (ERP) recordings have been used to study the neurophysiological correlates of recognition memory. Previous ERP research has demonstrated that on tasks of recognition memory, Old items elicit ERP responses that are more positive in electrical amplitude than the ERP responses elicited by New items, commonly referred to as ERP Old/New positivity effects. ERP Old/New positivity effects have been used to make inferences about cognitive processes mediating recognition memory, such as the early frontal Old/New positivity effect that has been associated with familiarity and the late parietal Old/New positivity effect that has been associated with recollection. These effects have been demonstrated different types of stimuli and on different types of recognition memory tasks. However, a systematic comparison of ERP Old/New positivity effects across different recognition memory tasks is lacking, particularly with respect to Remote Long-term memory. This thesis asked how ERP Old/New positivity effects differ between tasks of Short-term, Recent Long-term, and Remote Long-term memory tasks for faces. Experiment 1 simulated the condition of limited overt communication skills by analyzing the brain responses to memory stimuli, regardless of the overt behavioural response from healthy, “honest” participants. Experiment 2 examined the ERP responses of healthy participants instructed to feign a memory impairment. ERP Old/New positivity effects similar to those described in the experimental ERP literature were observed on the Short-term and Remote Long-term memory tasks in both Experiments 1 and 2. However, response accuracy was lower than expected on the Recent Long-term task resulting in weak ERP results. A comparison of the ERP Old/New responses between the Honest Response (Experiment 1) and the Simulated Memory Malingering (Experiment 2) groups found that despite differing overt behavioural responses, the ERP Old/New responses remained similar. The results demonstrate a similar electrophysiological mechanism mediating Short-term, Recent Long-term, and Remote Long-term recognition memory ERP responses, despite the different neuroanatomical substrates that have been proposed these different types of memory. Although an improved measure of Recent Long-term memory is needed, the results of this thesis are promising and demonstrate that ERP recordings could provide an objective instrument for measuring recognition memory functioning in clinical settings.

Orientadora: Profª Drª Raquel Vecchio Fornari / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Neurociência e Cognição, 2015. / O objetivo deste trabalho foi avaliar os efeitos da corticosterona na consolidação da memória recente e remota de ratos Wistar submetidos ao condicionamento de medo ao contexto. Os animais receberam 1 choque com duração de 1 segundo e intensidade de 0,6mA durante o treino e, em seguida, foi administrada uma injeção subcutânea de corticosterona nas doses de 0,3mg/kg, 1mg/kg, 3mg/kg ou salina. Os testes ocorreram em 2 dias e em 2 contextos distintos: o contexto do treino e um novo contexto. Os animais foram testados de forma contrabalanceada, ou seja, um grupo passou primeiro pelo contexto do treino enquanto o outro foi testado no novo contexto. No segundo dia, os animais foram testados no contexto oposto ao do primeiro dia, a fim de verificar se a ordem em que eram testados causaria alguma interferência na resposta de congelamento dos animais. Os resultados mostraram que a ordem em que foram expostos aos contextos não exerceu influência na resposta de condicionamento. Os animais testados 48 horas após o treino (memória recente), mostraram discriminar entre o contexto do treino e o novo contexto. Os animais que foram testados 29 dias após o treino (memória remota), apresentaram uma generalização do medo ao contexto. O mesmo grupo de animais que passou pelos testes de memória recente foi re-testado nos dois contextos 26 dias depois. Esses animais conseguiram discriminar entre os dois contextos, sugerindo que as sessões de teste para memória recente podem ter funcionado como sessões de reativação da memória. No entanto, em nenhum dos experimentos foi obtido resultado significativo com as diferentes doses de corticosterona em comparação com os animais do grupo controle. / The aim of this study was to evaluate the effects of corticosterone in the consolidation of recent and remote memory of Wistar rats subjected to contextual fear conditioning. For the 3 minutes training session, the animals received a footshock (1s, 0.6mA) after 2 minutes of free exploration. Immediately after training, the rats received corticosterone subcutaneously at doses of either 0.3mg/kg, 1mg/kg, 3mg/kg or saline. Two days later, the animals were tested in 2 different contexts in a counterbalanced fashion, that is, one group was first tested in the same context of training while the other was presented to a new context. On the second test day, the animals were tested in the opposite context to verify a possible effect of context order in their freezing response. The results showed that the order in which the rats were exposed to the contexts did not interfere with their responses. The animals tested for recent memory, 48 hours after training, discriminated between the training context and the new one. In turn, the animals tested 29 days after training, for remote memory, displayed a generalized fear to both contexts. The same group of animals that had gone through the recent memory test was re-exposed to both contexts 26 days later. The results revealed that these rats were still able to discriminate between the two contexts, suggesting that the recent memory test may have worked as a memory reactivation session. However, no effect of treatment with corticosterone was found in the experiments.

No description available.

Los cl'usters de computadores representan una soluci'on alternativa a los supercomputadores. En este tipo de sistemas, se suele restringir el espacio de direccionamiento de memoria de un procesador dado a la placa madre local. Restringir el sistema de esta manera es mucho m'as barato que usar una implementaci'on de memoria compartida entre las placas. Sin embargo, las diferentes necesidades de memoria de las aplicaciones que se ejecutan en cada placa pueden dar lugar a un desequilibrio en el uso de memoria entre las placas. Esta situaci'on puede desencadenar intercambios de datos con el disco, los cuales degradan notablemente las prestaciones del sistema, a pesar de que pueda haber memoria no utilizada en otras placas. Una soluci'on directa consiste en aumentar la cantidad de memoria disponible en cada placa, pero el coste de esta soluci'on puede ser prohibitivo. Por otra parte, el hardware de acceso a memoria remota (RMA) es una forma de facilitar interconexiones r'apidas entre las placas de un cl'uster de computadores. En trabajos recientes, esta caracter'¿stica se ha usado para aumentar el espacio de direccionamiento en ciertas placas. En este trabajo, la m'aquina base usa esta capacidad como mecanismo r'apido para permitir al sistema operativo local acceder a la memoria DRAM instalada en una placa remota. En este contexto, una plani¿caci'on de memoria e¿ciente constituye una cuesti'on cr'¿tica, ya que las latencias de memoria tienen un impacto importante sobre el tiempo de ejecuci'on global de las aplicaciones, debido a que las latencias de memoria remota pueden ser varios 'ordenes de magnitud m'as altas que los accesos locales. Adem'as, el hecho de cambiar la distribuci'on de memoria es un proceso lento que puede involucrar a varias placas, as'¿ pues, el plani¿cador de memoria ha de asegurarse de que la distribuci'on objetivo proporciona mejores prestaciones que la actual. La presente disertaci'on pretende abordar los asuntos mencionados anteriormente mediante la propuesta de varias pol'¿ticas de plani¿caci'on de memoria. En primer lugar, se presenta un algoritmo ideal y una estrategia heur'¿stica para asignar memoria principal ubicada en las diferentes regiones de memoria. Adicionalmente, se ha dise¿nado un mecanismo de control de Calidad de Servicio para evitar que las prestaciones de las aplicaciones en ejecuci'on se degraden de forma inadmisible. El algoritmo ideal encuentra la distribuci'on de memoria 'optima pero su complejidad computacional es prohibitiva dado un alto n'umero de aplicaciones. De este inconveniente se encarga la estrategia heur'¿stica, la cual se aproxima a la mejor distribuci'on de memoria local y remota con un coste computacional aceptable. Los algoritmos anteriores se basan en pro¿ling. Para tratar este defecto potencial, nos centramos en soluciones anal'¿ticas. Esta disertaci'on propone un modelo anal'¿tico que estima el tiempo de ejecuci'on de una aplicaci'on dada para cierta distribuci'on de memoria. Dicha t'ecnica se usa como un predictor de prestaciones que proporciona la informaci'on de entrada a un plani¿cador de memoria. El plani¿cador de memoria usa las estimaciones para elegir din'amicamente la distribuci'on de memoria objetivo 'optima para cada aplicaci'on que se est'e ejecutando en el sistema, de forma que se alcancen las mejores prestaciones globales. La plani¿caci'on a granularidad m'as alta permite pol'¿ticas de plani¿caci'on m'as simples. Este trabajo estudia la viabilidad de plani¿car a nivel de granularidad de p'agina del sistema operativo. Un entrelazado convencional basado en hardware a nivel de bloque y un entrelazado a nivel de p'agina de sistema operativo se han tomado como esquemas de referencia. De la comparaci'on de ambos esquemas de referencia, hemos concluido que solo algunas aplicaciones se ven afectadas de forma signi¿cativa por el uso del entrelazado a nivel de p'agina. Las razones que causan este impacto en las prestaciones han sido estudiadas y han de¿nido la base para el dise¿no de dos pol'¿ticas de distribuci'on de memoria basadas en sistema operativo. La primera se denomina on-demand (OD), y es una estrategia simple que funciona colocando las p'aginas nuevas en memoria local hasta que dicha regi'on se llena, de manera que se bene¿cia de la premisa de que las p'aginas m'as accedidas se piden y se ubican antes que las menos accedidas para mejorar las prestaciones. Sin embargo, ante la ausencia de dicha premisa para algunos de los benchmarks, OD funciona peor. La segunda pol'¿tica, denominada Most-accessed in-local (Mail), se propone con el objetivo de evitar este problema. / Cluster computers represent a cost-effective alternative solution to supercomputers. In these systems, it is common to constrain the memory address space of a given processor to the local motherboard. Constraining the system in this way is much cheaper than using a full-fledged shared memory implementation among motherboards. However, memory usage among motherboards may be unfairly balanced depending on the memory requirements of the applications running on each motherboard. This situation can lead to disk-swapping, which severely degrades system performance, although there may be unused memory on other motherboards. A straightforward solution is to increase the amount of available memory in each motherboard, but the cost of this solution may become prohibitive. On the other hand, remote memory access (RMA) hardware provides fast interconnects among the motherboards of a cluster computer. In recent works, this characteristic has been used to extend the addressable memory space of selected motherboards. In this work, the baseline machine uses this capability as a fast mechanism to allow the local OS to access to DRAM memory installed in a remote motherboard. In this context, efficient memory scheduling becomes a major concern since main memory latencies have a strong impact on the overall execution time of the applications, provided that remote memory accesses may be several orders of magnitude higher than local accesses. Additionally, changing the memory distribution is a slow process which may involve several motherboards, hence the memory scheduler needs to make sure that the target distribution provides better performance than the current one. This dissertation aims to address the aforementioned issues by proposing several memory scheduling policies. First, an ideal algorithm and a heuristic strategy to assign main memory from the different memory regions are presented. Additionally, a Quality of Service control mechanism has been devised in order to prevent unacceptable performance degradation for the running applications. The ideal algorithm finds the optimal memory distribution but its computational cost is prohibitive for a high number of applications. This drawback is handled by the heuristic strategy, which approximates the best local and remote memory distribution among applications at an acceptable computational cost. The previous algorithms are based on profiling. To deal with this potential shortcoming we focus on analytical solutions. This dissertation proposes an analytical model that estimates the execution time of a given application for a given memory distribution. This technique is used as a performance predictor that provides the input to a memory scheduler. The estimates are used by the memory scheduler to dynamically choose the optimal target memory distribution for each application running in the system in order to achieve the best overall performance. Scheduling at a higher granularity allows simpler scheduler policies. This work studies the feasibility of scheduling at OS page granularity. A conventional hardware-based block interleaving and an OS-based page interleaving have been assumed as the baseline schemes. From the comparison of the two baseline schemes, we have concluded that only the performance of some applications is significantly affected by page-based interleaving. The reasons that cause this impact on performance have been studied and have provided the basis for the design of two OS-based memory allocation policies. The first one, namely on-demand (OD), is a simple strategy that works by placing new pages in local memory until this region is full, thus benefiting from the premise that most of the accessed pages are requested and allocated before than the least accessed ones to improve the performance. Nevertheless, in the absence of this premise for some benchmarks, OD performs worse. The second policy, namely Most-accessed in-local (Mail), is proposed to avoid this problem / Serrano Gómez, M. (2013). Scheduling Local and Remote Memory in Cluster Computers [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/31639