Browsing by Subject "Episodic memory"
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Item Associations between sleep and memory in aging(2016-05) Sherman, Stephanie Michelle; Schnyer, David M.; Beevers, Christopher G; Haley, Andreana P; Westerberg, Carmen EThe goal of this dissertation was to understand how changes in sleep influence memory performance in healthy older adults. Previous research suggests that older individuals experience parallel declines in sleep and episodic memory. These age-related changes appear to be linked such that sleep disruptions contribute to deficits in memory performance. We examined the components of episodic memory that changed following sleep loss and correlated with aspects of sleep physiology. Healthy older adults completed two overnight sessions: an in-lab sleep recording session and a 24-hour sleep deprivation session. The morning after each sleep manipulation, participants completed both episodic memory and sustained attention tasks. We applied computational models, specifically drift-diffusion models, to the episodic memory tasks to examine whether sleep loss affected memory indirectly through lapses in sustained attention (vigilance hypothesis) or specifically through declines in the strategic processes associated with memory (neuropsychological hypothesis). Our results showed that memory functions that depend on processes associated with the prefrontal cortex were impaired following sleep deprivation. In addition, sleep loss caused a small but robust impairment in sustained attention. Since multiple cognitive processes were impaired by sleep loss in older adults, these findings do not provide unequivocal support for either the neuropsychological hypothesis or the vigilance hypothesis. In addition, we explored which aspects of sleep physiology (recorded during the sleep session) optimized components of memory performance. Our results illustrated that more slow wave power during sleep was correlated with higher next-day source memory strength. Additionally, individuals who spent more time in slow wave sleep had better memory retention. These results support further efforts to investigate sleep as a general indicator of cognitive function across the lifespan and highlight the importance of reinforcing healthy sleep behaviors as a method to preserve cognitive functioning in older adults.Item Reward modulation of medial temporal lobe function during associative encoding and cued recall(2010-05) Wolosin, Sasha Monica; Preston, Alison R.; Beer, Jennifer S.Emerging evidence suggests that hippocampal memory processing is modulated by midbrain regions under conditions of reward, resulting in enhanced encoding of episodic information—long-term memory for events. Current theories further suggest that hippocampal subregions may have distinct roles in episodic memory formation, and may be differentially influenced by dopaminergic midbrain inputs. Using high-resolution functional magnetic resonance imaging (fMRI), the present study investigated hippocampal subregional function as well as activation in surrounding medial temporal lobe (MTL) cortex, midbrain, and nucleus accumbens during associative encoding and cued recall under varying conditions of reward. A high-value or low-value monetary cue preceded a pair of objects indicating potential reward for successful retrieval of the association. At test, participants performed cued recall followed by match (correct association) or mismatch (incorrect association) probe decisions and received feedback on their performance. Behaviorally, cued recall performance was superior for pairs preceded by high reward cues at encoding relative to pairs preceded by low reward cues. FMRI analysis revealed regions within hippocampus, parahippocampal cortex, nucleus accumbens, and midbrain showing subsequent memory effects (greater encoding activation for remembered, compared to forgotten associations) and reward effects (greater activation for high-value, compared to low-value associations) during stimulus encoding. Within several of these regions, individual differences in reward-related encoding activation were correlated with the degree of the behavioral reward effect (better memory for high-value compared to low-value object pairs). At retrieval, regions in midbrain and subiculum predicted successful associative recall, and regions within hippocampus, parahippocampal cortex, nucleus accumbens, and midbrain showed reward effects in the absence of explicit reward cues. Within several MTL regions, activation was greater for match than mismatch probes. These findings are consistent with theories suggesting that reward-based motivation influences memory formation through interactions between dopaminergic midbrain and hippocampus.Item When memories relate: medial temporal and prefrontal contributions to memory integration and inference(2015-05) Schlichting, Margaret Lynn; Preston, Alison R.; Church-Lang, Jessica A; Colgin, Laura L; Lewis-Peacock, Jarrod A; Poldrack, Russell A; Schnyer, David MMemory is of immeasurable importance to the human experience. It has been known for decades that memory for individual events is supported by the medial temporal lobes (MTL), which include the hippocampus and adjacent cortex. Emerging research suggests that by retrieving related prior experiences during new learning, connections can also be formed among memories to create knowledge that spans events. Such integration mechanisms might be further influenced by memory models stored in medial prefrontal cortex (PFC), which serve to guide learning-phase retrieval and integrate across related memories. In contrast, lateral PFC might maintain separate representations for related events, consistent with its role in resolving interference. This dissertation used functional magnetic resonance imaging (fMRI) in humans to investigate the MTL and PFC mechanisms that link content across episodes. The first experiment investigated the contributions of hippocampal subfields to this encoding mechanism. Consistent with its hypothesized role in detecting inconsistencies and integrating across memories, integration signatures were isolated to the hippocampal CA1 subfield. The second experiment interrogated two aspects of offline processes that promote integration. First, neural evidence for reinstatement of initially learned content and enhanced hippocampal communication with content-specific visual regions during rest was associated with a behavioral index of integration. Moreover, enhanced functional connectivity between hippocampus and medial PFC both during and immediately following learning of related information was associated with better integration. This relationship was mirrored in hippocampal-medial PFC white matter integrity. The third experiment interrogated the nature of the hippocampal and prefrontal representations that underlie memory integration. Results revealed dissociable integration and separation signatures in hippocampus and PFC, highlighting how neural representations of memory elements can simultaneously promote integration across related events and protect from interference. In line with computational theory, these effects were also modulated by the manner in which events were experienced. Taken together, these studies provide insight into the neural mechanisms supporting the dynamic interactions among related memories. More broadly, this dissertation represents an important shift in the scientific study of memory, from exploring memory for individual events to investigating how memories may be derived across experiences to support appropriate action in novel situations.