The Role of Hippocampal Theta Phase in Human Memory Encoding

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Project Summary Abstract Episodic memory depends on the hippocampus and is thought to involve its rhythmic neural activity in the theta-frequency band (approximately 3-8 Hz). The phase of the hippocampal theta oscillation in rodents is thought to determine whether hippocampal processing is optimized for memory encoding versus retrieval by biasing information flow in versus out of the hippocampus. However, neither the theta phase-dependence nor the relationship between theta power and memory have been adequately tested in humans. This research and training plan aims to address this by experimentally testing memory in human subjects undergoing neurosurgical procedures that allow for direct recording of the hippocampal theta rhythm. Specifically, these experiments will be performed in adults with epilepsy who are undergoing clinically necessary invasive electrophysiological recording. A novel memory paradigm will be used to identify the relationship between measured phase angles and power of the hippocampal theta oscillation and the success of specific memory encoding events. Next, we will directly test the role of hippocampal theta power and phase in memory encoding using direct electrical stimulation. Stimulation will be delivered to the hippocampal network in order to entrain the theta oscillation. We will then assess the impact of this manipulation on memory encoding ability. Findings may improve understanding of hippocampal neural mechanisms for learning and memory and inform treatment of memory disorders. This research will provide the applicant, a student seeking a Ph.D. in neuroscience, with training in sophisticated cognitive neuroscience experimentation on human memory using invasive electrophysiology methods. This learning experience will be complemented by relevant coursework, workshops, and mentored instruction in research design and methods, analytics, oral and written scientific communication, and professional development.