Differential Mnemonic Contributions of Cortical Representations during Encoding and Retrieval.
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2024-10
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Abstract
Several recent fMRI studies of episodic and working memory representations converge on the finding that visual information is most strongly represented in occipito-temporal cortex during the encoding phase but in parietal regions during the retrieval phase. It has been suggested that this location shift reflects a change in the content of representations, from predominantly visual during encoding to primarily semantic during retrieval. Yet, direct evidence on the nature of encoding and retrieval representations is lacking. It is also unclear how the representations mediating the encoding-retrieval shift contribute to memory performance. To investigate these two issues, in the current fMRI study, participants encoded pictures (e.g., picture of a cardinal) and later performed a word recognition test (e.g., word "cardinal"). Representational similarity analyses examined how visual (e.g., red color) and semantic representations (e.g., what cardinals eat) support successful encoding and retrieval. These analyses revealed two novel findings. First, successful memory was associated with representational changes in cortical location (from occipito-temporal at encoding to parietal at retrieval) but not with changes in representational content (visual vs. semantic). Thus, the representational encoding-retrieval shift cannot be easily attributed to a change in the nature of representations. Second, in parietal regions, stronger representations predicted encoding failure but retrieval success. This encoding-retrieval "flip" in representations mimics the one previously reported in univariate activation studies. In summary, by answering important questions regarding the content and contributions to the performance of the representations mediating the encoding-retrieval shift, our findings clarify the neural mechanisms of this intriguing phenomenon.
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Howard, Cortney M, Shenyang Huang, Mariam Hovhannisyan, Roberto Cabeza and Simon W Davis (2024). Differential Mnemonic Contributions of Cortical Representations during Encoding and Retrieval. Journal of cognitive neuroscience, 36(10). pp. 2137–2165. 10.1162/jocn_a_02227 Retrieved from https://hdl.handle.net/10161/31616.
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Cortney Howard
Shenyang Huang
Roberto Cabeza
My laboratory investigates the neural correlates of memory and cognition in young and older adults using fMRI. We have three main lines of research: First, we distinguish the neural correlates of various episodic memory processes. For example, we have compared encoding vs. retrieval, item vs. source memory, recall vs. recognition, true vs. false memory, and emotional vs. nonemotional memory. We are particularly interested in the contribution of prefrontal cortex (PFC) and medial temporal lobe (MTL) subregions and their interactions. Second, we investigate similarities and differences between the neural correlates of episodic memory and other memory and cognitive functions (working, semantic, implicit, and procedural memory; attention; perception, etc.). The main goal of this cross-functional approach is to understand the contributions of brain regions shared by different cognitive functions. Finally, in both episodic memory and cross-function studies, we also examine the effects of healthy and pathological aging. Regarding episodic memory, we have linked processes differentially affected by aging (e.g., item vs. source memory, recall vs. recognition) to the effects of aging on specific PFC and MTL subregions. Regarding cross-function comparisons, we identify age-related changes in activity that are common to various functions. For example, we have found an age-related increase in bilaterality that occurs for many functions (memory, attention, language, perception, and motor) and is associated with functional compensation.
Simon Wilton Davis
My research centers around the use of structural and functional imaging measures to study the shifts in network architecture in the aging brain. I am specifically interested in changes in how changes in structural and functional connectivity associated with aging impact the semantic retrieval of word or fact knowledge. Currently this involves asking why older adults have particular difficulty in certain kinds of semantic retrieval, despite the fact that vocabularies and knowledge stores typically improve with age.
A second line of research involves asking questions about how this semantic system is organized in young adults, understanding which helps form a basis for asking questions about older adults. To what degree are these semantic retrieval processes lateralized? What cognitive factors affect this laterality? How are brain structures like the corpus callosum involved in mediating distributed activation patterns associated with semantic retrieval?
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