Browsing by Subject "Medial prefrontal cortex"
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Item Using the neural level of analysis to understand the computational underpinnings of positivity biases in self-evaluation(2012-05) Hughes, Brent Laurence, 1981-; Beer, Jennifer S., 1974-; Gosling, Samuel D.; Neff, Lisa A.; Preston, Alison A.; Swann, Jr., William B.Decades of research have demonstrated that people sometimes provide self-evaluations that emphasize their most flattering qualities. Different theoretical accounts have been offered to explain the mechanisms underlying positively-biased self-evaluation. Some researchers theorize that positively-biased self-evaluations arise from a self-protection motivation because positivity biases increase in situations of heightened self-esteem threat. Alternative views question whether self-protection motivation is a necessary or even dominant source of positivity bias by demonstrating that positively-biased self-evaluations occur even when threat is not heightened, and that a general judgment approach leads to positivity biases in some domains but also to negativity biases in other domains. One reason for this gap in knowledge is that behavioral measures are limited in their ability to resolve whether the processes underlying positively-biased self-evaluation are the same or different depending on contextual motivators. Neuroimaging methods are well suited to examine whether different mechanisms underlie similar behaviors, specifically similar positively-biased responses in different contexts. The four studies presented here explore the neural mechanisms of positively-biased self-evaluation by first identifying a core set of neural regions associated with positivity bias (Study 1A and 1sB), examining whether a heightened self-protection motivation changes the engagement of those neural systems (Study 2), and specifying the precise mechanisms supported by those regions (Study 3). Studies 1A and 1B revealed evidence for a neural system comprised of medial and lateral orbitofrontal cortex (OFC) and, to a lesser extent dorsal anterior cingulate (dACC) that was modulated by positivity bias. Study 2 found that a heightened self-protection motivation changes the engagement of medial OFC in positively-biased self-evaluation. Finally, Study 3 found evidence that medial OFC may support a common mechanism in positively-biased judgment that is implemented differently as a function of the motivational context. Taken together, these studies represent a first step toward developing a neural model of positively-biased self-evaluation. The findings provide some preliminary evidence that positivity biases may represent distinct processes in different motivational contexts. This dissertation sets the stage for future work to examine how specific positively-biased cognitive mechanisms may be supported by specific neural systems and computations as a function of motivational contexts.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.