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Episodic memory retrieval enables the recollection of personal experiences and is driven by an extensive network of brain regions. Little is known, however, about the functional connectivity in the brain during episodic memory retrieval. Previous research has shown the importance of theta oscillations, or brain activity occurring at 3-8 Hz, during the retrieval process. Theta oscillations modulate interactions between the frontal cortex, parietal cortex, and hippocampus (frontal-parietal-hippocampal network) during memory-related cognitive processes (Nyhus & Curran, 2010). However, the directional flow of information between these brain regions is unclear. Based on previous work (Nyhus & Curran, 2010; Anderson et al., 2010), it was expected that at theta frequency there is directed information flow from the left inferior parietal cortex to the right dorsolateral prefrontal cortex (dlPFC). The present study applied a type of Granger causality analysis, specifically renormalized Partial Directed Coherence, to measure the directional flow of information in previously recorded electroencephalography (EEG) data during a source and item episodic memory retrieval task. Using the EEGLAB toolbox groupSIFT (Source Information Flow Toolbox), across-subject Granger causality analysis was performed on the EEG data. One connection of interest was from the right precuneus region in the parietal lobe to the right superior frontal lobe (which contains the dlPFC), summed t = 137, p < 0.05. This suggests the preliminary importance of theta oscillations in transient network dynamics during post-retrieval monitoring in episodic memory. Continued research will further analyze this preliminary, exploratory work which identified the potential relevance of the precuneus in source memory retrieval.
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