Identifying the role of theta oscillations in the transient network dynamics involved in episodic memory

Bowdoin College, Brunswick ME

Investigators

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Abstract

7. Project Summary/Abstract Episodic memory is a complex cognitive function that involves many interacting brain regions and allows us to store the content of experience that can be retrieved later. Coordination of prefrontal cortex, [parietal cortex,] and medial temporal regions is critical for the cognitive control of memory and neural oscillations may provide the means by which these brain regions interact. Although recent research using electroencephalography (EEG) has demonstrated that neural oscillations in specific frequency bands, such as theta (4-8 Hz) frequency, correlates with memory performance, the transient network dynamics have not been specified and it is not clear whether theta oscillations play a causal role in information processing in episodic memory systems. Our long-term goal is to contribute to understanding the role of oscillatory dynamics in episodic memory. The objective of the proposed research is to establish the transient network dynamics and a causal role of theta oscillations in [post-retrieval monitoring in] episodic memory. Based on preliminary data, the central hypothesis is that there is transient directed information flow [from left inferior parietal cortex (IPC) to right dorsolateral prefrontal cortex (DLPFC)] and that non-invasive brain stimulation at theta frequency will lead to changes in oscillatory dynamics and improved memory performance. To test this hypothesis, in two specific aims, Granger causality analysis, transcranial alternating current stimulation (tACS), and EEG will be used to: 1) Determine the directional flow of information [in post-retrieval monitoring] and 2) Identify the oscillation-specific parameters that support retrieval success. In Aim 1, Granger causality analysis will be used to analyze EEG data recorded during three episodic memory experiments. In Aim 2, tACS and EEG will be used to compare oscillatory power, coherence, Granger causality values, and memory performance following stimulation at specific frequencies (theta, control, sham) during [encoding and retrieval] of a source memory task. The proposed research is innovative because it moves beyond correlational analysis and seeks to apply Granger causality analysis to EEG data and to combine non-invasive brain stimulation (tACS) and EEG to understand the transient network dynamics involved in episodic memory. Core data provided by the proposed research is significant as it is an important step towards understanding the transient, systems-level interactions that support the cognitive control of episodic memory in the normal functioning brain. Basic knowledge gained about neural oscillatory dynamics in episodic memory is applicable to a number of brain disorders. Mental illness such as anxiety disorders, autism, depression, and schizophrenia show disruption of oscillatory dynamics and lead to deficits in episodic memory. As such, the proposed research could inform both diagnostic guidelines and the development of novel non-invasive treatments for memory dysfunction in mental illness.