Semantic contributions to episodic memory

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This application describes a 3-year training plan that will enable me, a cognitive neuroscientist with a background in memory consolidation and neuroimaging methods, to conduct research on the interaction between semantic knowledge and episodic memory. Co-supervised by Dr. Sharon Thompson-Schill, an expert in the field of the cognitive and neural organization of concepts and semantic knowledge, and Dr. H. Branch Coslett, a neurologist with extensive experience in brain stimulation, I propose to examine how semantic knowledge shapes new episodic memories, and how changes their cortical representation may determine the extent to which episodic memories are influenced by semantic knowledge. The proposed experiments aim to address two gaps in the literature on semantic knowledge and episodic memory consolidation. First, memory consolidation research typically treats new episodic memories as distinct (orthogonalized) from other past experiences, when in reality, episodic memories are virtually always made up of re-combinations of elements (e.g. locations, places, objects) for which we already have acquired rich semantic knowledge. How such semantic elements interact with, or bias, new episodic elements in memories over time is unclear. Second, past work investigating the role of prior knowledge on new memories is often focused on how prior knowledge facilitates the encoding and retrieval of new memories, rather than how they may be biased by prior knowledge. To address this limitation of prior work, I propose a series of experiments that probe how semantic knowledge systematically biases episodic memories, and how this bias may be influenced by the representation of the memory in the anterior temporal lobe (ATL), a cortical structure critical for intact semantic knowledge. In Aim 1, I propose a behavioral experiment that leverages the hierarchical organization of semantic knowledge, namely category typicality and levels of abstraction, to understand how semantic knowledge influences new episodic memories. I employ a continuous measure of retrieval to disentangle biases driven by semantic knowledge from errors due to forgetting. In Aim 2, I adapt this experiment for patients with post-stroke lesions to understand how specific impairments in category knowledge influence retrieval. While I outline specific predictions for patients with greater extent of damage in ATL, I adopt an exploratory approach to identify other potential sites of integration between semantic and episodic information. In Aim 3, I employ transcranial magnetic stimulation to test whether episodic memories are more biased by semantic knowledge as they become increasingly represented in ATL over time. The proposed research will contribute to our understanding of the neural mechanisms underlying the contributions of semantic knowledge to new episodic memory, and it may inspire novel rehabilitation strategies for individuals suffering from memory impairments.