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Restricted Access Thesis

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Erika Nyhus


Functional circuits have been shown to exist between different brain regions during the retrieval of memories. Furthermore, it has been posited that neural oscillations provide a mechanism of interaction between these regions. The present study focuses on two regions known to be involved in episodic memory retrieval, the inferior parietal cortex (IPC) and the dorsolateral prefrontal cortex (dlPFC). We examined whether theta-band oscillations play a role in the bidirectional communication between these regions and if there is more activity flowing in one direction versus the opposite. EEG data was collected as subjects completed a source memory task that involved an encoding phase with 200 words and a retrieval phase with 400 words, half of which were new. Depending on the category, subjects were instructed to either imagine or to pronounce backwards to themselves, each of the 200 words during encoding, and then had to recall not only whether they were old versus new, but also under which category they were previously seen. Using EEG recording and Granger causality analysis, we can examine the causal relationship between theta oscillations in both regions and determine the directionality of the flow of information. While we originally posited that there would be increased directional flow of information from inferior parietal cortex to prefrontal cortex, results show a higher flow of information in the opposite direction (PFC  IPC), although our hypothesis of overall increased activity for hits versus correct rejections was confirmed.


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