Repetition and the passage of time influence the consolidation of long-term episodic memories. The experiments presented here have explored the influence of repetition on recent and remote autobiographical memories both behaviorally with regard to qualitative and quantitative measures of content, and neuroanatomically, focusing on changes within the hippocampus and adjacent structures. The first experiment tested the prediction made by MTT that hippocampal memory traces expand and strengthen as a function of repeated memory retrievals. An fMRI paradigm was used to compare the effect of memory retrieval versus the mere passage of time on hippocampal activation. Participants retrieved remote autobiographical memories that had been previously retrieved either one month earlier, two days earlier, or multiple times during the preceding month. Behavioral analyses revealed that the number and consistency of memory details retrieved increased with multiple retrievals but not with the passage of time. Hippocampal activation did not change as a function of either multiple retrievals or the passage of time. The second behavioral investigation was a follow-up to the first experiment, examining the retrieval of those same memories one year later in order to determine whether the level of detail remained stable or whether the memories returned to their original state. Participants reported even more details than they had recalled at least one year earlier, including new details. This finding was consistent across both multiple and single retrieval conditions. These findings together with those of the first study suggest that both repetition and the passage of time are important factors that may result in an increase in recall. The third and final experiment explored the behavioral and neural influences of repeated reactivation of both recent and remote autobiographical memories. Participants were interviewed a total of five times throughout one month and retrieved 20 significant life event memories, from either within the past several months or more than five years ago. Additionally, two fMRI scan sessions were collected, which enabled a direct comparison of the same 20 memories before and after a series of repetitions. Activation increased with repetition in several brain regions including bilateral posterior cingulate and precuneus. Behaviorally, repetition resulted in increased accessibility as suggested by decreased reaction times between the initial and final retrieval sessions, and a general maintenance of the level of recall resulted with repetition.

The hippocampus and non-hippocampal long-term memory systems each have the capacity to learn and express contextual fear memory. How these systems interact during learning and remembering revolves around hippocampal mediated interference, where the hippocampus dominates for both the acquisition and expression of long-term memory. Hippocampal interference during learning can be overcome by modifying learning parameters such that learning is distributed across multiple independent sessions. The standard view of the role of the hippocampus in long-term memory retrieval is that it is temporally limited, where recently acquired memory is dependent on hippocampal function though as a memory ages, dependency is transferred to other memory systems by a process called systems consolidation. Distributed training demonstrates that learning parameters create a memory that is resistant to hippocampal damage. We find little evidence to support temporally based systems consolidation, and present data that supports the view that if the hippocampus is initially involved in learning a memory, it will always be necessary for accurate retrieval of that memory. A critical assessment of the rat literature revealed that initial memory strength, and/or lesion techniques might be responsible for the few studies that report temporally graded retrograde amnesia using contextual fear conditioning. Our experiments designed to directly test these possibilities resulted in flat gradients, providing further evidence that the hippocampus plays a permanent role in long-term memory retrieval. We propose and assess alternatives to the standard model and conclude that a dual store model is most parsimonious within the presented experiments and related literature. Interactions of the hippocampus and non-hippocampal systems take place at the time of learning and remembering, and are persistent over time. / xvi, 161 leaves : ill. (some col.) ; 29 cm

Thesis (Ph. D.)--University of California, San Diego, 2007. / Title from first page of PDF file (viewed November 7, 2007). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of California, San Diego, 2009. / Title from first page of PDF file (viewed April 1, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 150-163).

Thesis supervisor: Steven J. Luck. Thesis supervisor: Andrew Hollingworth. Includes bibliographical references (p. 125-128).

Thesis (Ph. D.)--University of California, San Diego, 2009. / Title from first page of PDF file (viewed September 15, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.

Thesis (M.A.)--Miami University, Dept. of Psychology, 2005. / Title from first page of PDF document. Document formatted into pages; contains [1], iv, 35 p. : ill. Includes bibliographical references (p. 32-35).

Thesis (M.Sc.)--Memorial University of Newfoundland, 2003. / Bibliography: leaves 48-57. Also available online.

Choisir une source de nourriture adaptée à ses besoins est d'une importance vitale. Cette sélection est basée sur des indices sensoriels mais la valeur nutritive réelle des aliments consommés ne peut être évaluée qu'après son ingestion par les senseurs métaboliques internes. Se rappeler cette valeur requiert un type particulier de mémoire associative car les indices sensoriels présents durant la sélection et la consommation de la nourriture doivent être associés à une information métabolique disponible après un délai. Les mécanismes de ce type d'association restent à décrire. La drosophile représente un modèle de choix pour ce type d'étude car les outils génétiques disponibles permettent la manipulation de l'expression génique et de l'activité neurale avec une grande précision. Associer une odeur avec un sucre chez des drosophiles à jeun induit la formation de mémoire associative à court terme (MCT) qui perdure quelques heures. Si le sucre est énergétique, on observe la formation d'une mémoire associative à long terme (MLT) perdurant plusieurs jours. Nous avons entrepris d'identifier spécifiquement les mécanismes de formation de la MLT appétitive.Nous avons pu démontrer que la formation de la MLT se fait en deux étapes : premièrement une association goût/odeur est formée, puis un rétrocontrôle métabolique intervient de façon différée pour consolider à long terme cette association si l'ingestion est suivie dans les premières heures d'un apport énergétique. Bien que la signalisation AMPc/PKA soit centrale pour les formations de la MCT et de la MLT, cette dernière requiert des réseaux neuronaux différents et fait appel à des acteurs moléculaires de la voie spécifiques. / Food selection according to energetic requirement is crucial. This selection is based on sensory cues, but true nutritious content is evaluated by a post-ingestion mechanism. Remembering this value requires to associate sensory cues available during food selection and consumption with metabolic information available only after a long delay that can exceed one hour. Mechanisms of such associations are poorly known.Drosophila represents a good model for this type of study since available genetic tools allow a fine control of genetic expression and neuronal activity. Association between an odor and sugar in starved flies induces short-term memory formation (STM) lasting for a couple of hours when the sugar is not energetic but induces the formation of long-term memory (LTM) lasting for days when it is energetic. We have tried to identify specific mechanisms of appetitive LTM formation.We showed that LTM formation is a two-step process: first, an odor/taste association is made. Then a delayed metabolic feedback acts in order to consolidate this association into LTM if sugar ingestion is followed by energetic supply within the three first hours. Although cAMP/PKA-signaling pathway is a central process for both STM and LTM formation, the last one involves different neural networks and needs specific molecular actors.

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