Investigating the Neural Mechanisms of Memory Retrieval

We rely on our episodic memory, the memory for personally experienced events, to remember the last vacation we took or to remember what was for dinner last night. In this dissertation, I use electroencephalographic (EEG) recordings to measure the neural correlates of episodic memory retrieval. I collected EEG recordings across a series of recognition memory tasks in which participants studied words or images and then were tested on their memory for those items. In the first chapter, I use pattern classification analyses to measure neural evidence for a retrieval brain state, a whole-brain activity/connectivity pattern that is engaged when an individual attempts to access a stored representation. I find that greater temporal overlap - the distance in time between two experiences - leads to automatic induction of the retrieval state and impairs memory of past events. In the second chapter, I investigate memory and decision making processes during retrieval. I find distinct processes occur prior to and following a memory response that are modulated by successful retrieval. In the next chapter I measure post-response feedback signals using pattern classification analyses. I find that post-retrieval neural signals reflect an intrinsic reward signal in response to successful retrieval. In the final chapter, I show that the memory benefit for extrinsic reward following retrieval may be dependent on the strength of the memory that is retrieved.