http://hdl.handle.net/1721.1/7776 Search the Channel search http://dspace.mit.edu/simple-search http://hdl.handle.net/1721.1/34484 Title: Dendritic sensitivity to the direction of synaptic firing mediated by inhibition; and, The effects of the release timecourse of neurotransmitter on synaptic transmission <br/> <br/>Authors: Krupa, Boris <br/> <br/>Description: Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 2006.; Includes bibliographical references. http://hdl.handle.net/1721.1/33674 Title: Selective attention and the visual representation of object attributes in the ventrolateral prefrontal cortex and anterior cingulate cortex of the rhesus monkey <br/> <br/>Authors: Kiddoo, Cynthia E <br/> <br/>Abstract: The effects of attending to one or another of an object's attributes on neuronal representations of that object were investigated using extracellular recordings. A female rhesus monkey performed a delayed match to object attribute (DMSA) task, in which she alternately matched object orientations and object colors. In half of the task conditions, only one attribute matched the sample, forcing the animal to apply the current matching rule and ignore the irrelevant-attribute. Multiple simultaneous single-unit extracellular recordings were made in the ventrolateral prefrontal cortex (VLPFC) and anterior cingulate cortex (ACC) while the monkey performed the task. Neuronal selectivity for matching rule, object attributes, attribute relevance, response choice, and congruency were assessed using multi-factor ANOVAs. Attribute-selective responses were common in both cortical areas during the sample and delay periods, but were not significantly modulated by attribute relevance. There were few interactions between color-selective and orientation-selective responses according to the ANOVAs, suggesting that these attributes were represented independently.; (cont.) Significant effects of attribute relevance, response choice, and congruency appeared in both areas after the delay period, when the probe appeared onscreen. VLPFC cells were more active during incongruent and non-match conditions, when responses had to be suppressed. ACC cells were more active during congruent and match conditions, when active response suppression was not required. The results indicate that although prefrontal cortex often shows a bias for relevant information (Rainer et al, 1998), it may not do so if the task requires frequent alternation of attentional sets or active suppression of conflicting responses. The data also indicate that the VLPFC's role in managing attentional 'set' (Banich et al, 2000; Milham et al, 2001) is performed in conjunction with active stimulus comparison and response selection (e.g., Rushworth et al, 1997), not during working memory maintenance. The ACC may facilitate the reactivation of response tendencies that had been actively suppressed, possibly as part of a larger role in managing response conflict (Botvinick et al, 2004). <br/> <br/>Description: Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 2005.; Includes bibliographical references (p. 52-56). http://hdl.handle.net/1721.1/35700 Title: Phase-locking of neurons in the hippocampus and the medial prefrontal cortex of the rat to the hippocampal theta rhythm <br/> <br/>Authors: Lubenov, Evgueniy V <br/> <br/>Abstract: The interactions between cortical and hippocampal circuits are critical for memory formation, yet their basic organization at the neuronal network level is not well understood. Here we investigate the timing relationships between neuronal activity in the medial prefrontal cortex of freely behaving rats and the hippocampal theta rhythm. We demonstrate that a significant portion of prefrontal neurons are phase-locked to the hippocampal theta rhythm and we compare the phase-locking properties of prefrontal and hippocampal cells. We also show that prefrontal neurons phase-lock best to theta oscillations delayed by approximately 50 ms and confirm this hippocampo-prefrontal directionality and timing at the level of correlations between single cells. Finally we demonstrate that phase-locking of prefrontal cells is predicted by the presence of significant correlations with hippocampal cells at positive delays up to 150 ms, suggesting that direct hippocampal input has an important contribution to the observed prefrontal phase-locking. The theta entrained activity across cortico-hippocampal circuits described here may be important for gating information flow and guiding the plastic changes that are believed to underlie the storage of information across these networks. <br/> <br/>Description: Thesis (Ph. D. in Neuroscience)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 2005.; Includes bibliographical references (p. 53-59). http://hdl.handle.net/1721.1/37967 Title: The role of temporal factors and prior knowledge in causal learning and judgment <br/> <br/>Authors: Krynski, Tevye Rachelson <br/> <br/>Abstract: Causal relationships are all around us: wine causes stains; matches cause flames; foods cause allergic reactions. Next to language, it is hard to imagine a cognitive process more indicative of human intelligence than causal reasoning. To understand how people accomplish these feats, two major questions must be addressed: how do people acquire knowledge of causal relationships (causal learning), and how do people use that knowledge to make predictions and draw inferences (causal judgment)? The first part of this thesis is concerned with causal learning, and draws on the foundation of Bayesian inferential frameworks (e.g., Tenenbaum, Griffiths, & Kemp, 2006) to explain how observable data can be used to infer causal relationships between events. I will argue that rapid causal learning from small samples can be understood as rational inference over a representation of causality that includes a temporal delay between cause and effect. Experimentally, I show that people learn causal relationships faster when the temporal delay between cause and effect is less variable, just as is predicted by a rational statistical model of event causation. I argue that people's tendency to learn better from short delays is an artifact of the fact that short delays are inherently less variable.; (cont.) The second part of this thesis is concerned with causal judgment, and draws on the foundation of knowledge-based Bayesian networks to show that it is often more rational to make judgments using causal frameworks than purely statistical frameworks. Deviations from traditional norms of judgment, such as "base-rate neglect" (Tversky & Kahneman, 1974), can be explained in terms of a mismatch between the statistics given to people and the causal models they intuitively construct to support probabilistic reasoning. Experimentally, I provide evidence that base-rate neglect may be an artifact of applying causal reasoning to purely statistical problems. Six experiments show that when a clear mapping can be established from given statistics to the parameters of an intuitive causal model, people are more likely to use the statistics appropriately, and that when the classical and causal Bayesian norms differ in their prescriptions, people's judgments are more consistent with causal Bayesian norms. <br/> <br/>Description: Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 2006.; Includes bibliographical references (leaves 189-193).