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Why do we have such difficulty recalling words as we get older? Evidence that hippocampal declines underlie word-finding problems in aging
Poster A69 in Poster Session A, Thursday, October 6, 10:15 am - 12:00 pm EDT, Millennium Hall
Michael T. Ullman1, Lauren E. Russell1, David A. Balota2, Daniel Lipscomb3, George Luta1, Marcus Meinzer4, Michael D. Rugg5, Kyle F. Shattuck1, Peter E. Turkeltaub1, John W. VanMeter1, João Veríssimo6, Jana Reifegerste1,7; 1Georgetown University, Washington DC, USA, 2Washington University, St. Louis MO, USA, 3University of Virginia, Charlottesville VA, USA, 4University Medicine Greifswald, Greifswald, Germany, 5University of Texas at Dallas, Dallas TX, USA, 6University of Lisbon, Lisbon, Portugal, 7University of Potsdam, Potsdam, Germany
We often experience word-finding difficulties as we get older (“What is that word again?”). Deficits of executive function, processing speed, and perceptual abilities have each been posited as explanatory accounts for these problems. However, it remains uncertain whether these accounts best explain the pattern of lexical declines, or are sufficient to explain them. We propose that word-finding declines in aging are largely explained by concomitant declines in declarative memory, in particular hippocampal-related declines. We refer to this novel account as the declarative aging deficit (DAD) hypothesis. It is motivated by prior evidence suggesting first, that word learning and retrieval depend on declarative memory, including the hippocampus, and second, that declarative memory abilities, especially hippocampal metrics and functions, decline strikingly in aging. DAD therefore predicts declines particularly in lexical abilities that depend heavily on the hippocampus. Lexical production (reliant on hippocampal-based recollection) should be more affected than lexical comprehension (which can also rely on perirhinal-based familiarity). Particular problems should be found recalling words that have later ages-of-acquisition, such as newer words in the language (e.g., ‘sudoku’), which may have had less time than established words learned earlier in life (e.g. ‘pretzel’) to undergo systems consolidation, and thus may still rely substantially on the hippocampus. To test DAD we gave (thus far) 118 participants (ages 18-83) picture-naming (production) and word-picture matching (comprehension) tasks of both newer/recently-acquired and established/early-acquired words. Preliminary analyses revealed significant age-related lexical production declines for newer but not established words, while comprehension showed no declines at all. The analyses controlled for word frequency, word length, socio-economic status, education, amount of general lexical input, processing speed, and inhibitory control abilities, while also accounting for words unknown to each participant and screening for hearing/vision and Mild Cognitive Impairment. Moreover, hippocampal volumes (corrected for intracranial volumes) mediated the effect of age on the production of newer but not established words, even with other factors such as executive function and processing speed controlled for. Basic research and translational implications are discussed.
Topic Areas: Development, Meaning: Lexical Semantics