Comparison of fMRI and iEEG metrics of hippocampal connectivity during memory encoding

Ut Southwestern Medical Center, Dallas TX

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Abstract

PROJECT SUMMARY Two of the most widely-used methods of understanding human neurophysiology during episodic memory encoding are functional magnetic resonance imaging (fMRI) and intracranial electroencephalography (iEEG). However, the relationship between fMRI metrics of brain activity during memory processes and electrophysiological activity is unclear, especially for the hippocampus and associated structures. In preliminary work with iEEG and fMRI, we have used several methods to quantify hippocampal activity and connectivity during successful memory encoding. In our first aim, we intend to compare these methods by performing pre-operative fMRI in patients who subsequently undergo stereo EEG electrode implantation for seizure localization. These participants will perform the same memory task during both fMRI and iEEG recording, and we hypothesize that memory-related modulation of hippocampal connectivity to brain areas such as the posterior cingulate, angular gyrus, pre-frontal cortex, and lateral temporal cortex will be highly correlated between fMRI and iEEG. We believe hippocampal connectivity modulation will be more similar than activity within single brain sites. Our second aim is to use cortico-cortical evoked potential mapping to develop a complementary connectivity map for the hippocampus and compare these data to functional connectivity during memory encoding. The results of our research will inform fundamental questions of the neural basis of memory encoding and retrieval, including theories of phase coding and communication through synchrony during memory processes. Our results will also help improve predictive models for the magnitude of memory loss after temporal lobe surgery by integrating iEEG and fMRI information.