Browsing by Subject "prefrontal cortex"

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    Model-Free and Model-Based Influence on Choice in Rodents and Interactions between Hippocampus and Dorsomedial Prefrontal Cortex during Deliberation
    (2020-01) Hasz, Brendan
    Decision making is driven by multiple, somewhat independent systems within the brain. One of these systems makes slow, deliberative decisions, and is thought to be driven by a model-based neural algorithm, in that it learns an internal model of the world which it uses to make decisions. Another system makes fast, habitual choices, and is hypothesized to depend on a model-free neural algorithm, in that it does not learn a model of the world, but simply stores state-action-reward associations. While the habitual system is relatively well-studied, the neural underpinnings of the deliberative system are less clear. Specifically, it is not known how areas comprising the deliberative system, such as prefrontal cortex and the hippocampus, share information on fast timescales. Also, representations of contingency information in prefrontal areas have previously been impossible to disambiguate from the encoding of other time-varying information. In this thesis, we adapted for rats a task which enabled the dissociation of model-based from model-free influence on choice, and we found evidence for both model-based and model-free control. We also developed a simpler task which caused rats to repeatedly transition between deliberative and habitual modes. On this second task, we found that both dmPFC and CA1 encoded information about task contingencies, while simultaneously representing unrelated time-varying information. Lastly, we examined interactions between dmPFC and CA1 on fast timescales, and found that both areas represented prospective information simultaneously, but that the content of this prospective information was not always identical between the two areas. Activity in dmPFC predicted whether HPC would represent prospective information on broad timescales, and prospective representation in HPC changed reward encoding in dmPFC on faster, sub-second timescales. Our work begins to bridge the neural underpinnings of decision making in rodents and the algorithms by which they select actions, confirms that the deliberative system represents contingency information, and uncovers asymmetries in the transfer of information between dmPFC and HPC.
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    Prefrontal cortex development following variations in early life experience: Cognitive and neural correlates
    (2016-09) Hodel, Amanda
    Human brain development is not linear. Prefrontal cortex, typically considered a “late- developing” brain region, undergoes its most rapid development over the first years of life. Early and extended sensitivity of prefrontal cortical circuits to the environment allows maximum potential for infants to benefit from positive experiences, but can become a risk factor if the environment is non-optimal. The goal of the current studies was to characterize the dynamic influence of early experience on the development of prefrontal cortex structure, function, and dependent behaviors across developmental. We examined concurrent and long-term correlates of early risk in two different populations of children: children born moderate-to-late preterm (PT; 32-36 weeks gestation) and children adopted from orphanage care prior to five years of age (post-institutionalized or PI children). In Study 1 we characterized the structure of higher-level, prefrontal- dependent cognitive skills in 9-month-old infants and described the behavioral correlates of exposure to early biological risk (moderate-to-late PT birth) and of normative variations in the familial environment. In Study 2 we examined prefrontal cortex development in adolescents born moderate-to-late PT using structural and functional neuroimaging measures. In Study 3 we documented impacts of early deprivation on the connectivity of frontal-lobe systems in adolescents adopted from early orphanage care. Across studies, we found evidence that early adversity shapes both concurrent and long- term prefrontal cortex development. In healthy, moderate-to-late preterm infants, lower gestational age at birth was associated with poorer performance on five of six early executive function tasks (Study 1a), perhaps driven by underlying differences in early attention shifting skills (Study 1b). Adolescents born moderate-to-late PT had reduced prefrontal cortex volume and altered prefrontal functional activity during an executive function task in comparison to full-term controls (Study 2), suggesting developmental continuity in atypical prefrontal cortex development following moderate-to-late PT birth. Impacts of early orphanage rearing on prefrontal systems were also not fully ameliorated by adolescence. PI youth had reduced cortical white matter volume and poorer white matter microstructural integrity across the brain, including in fronto-limbic and fronto- striatal tracts. These findings highlight the plasticity and vulnerability of prefrontal circuits during the first years of life.