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Everything, everywhere, not as one: A high-resolution investigation of the neural correlates of unitization in aging within the medial temporal lobe

Poster Session A - Saturday, March 7, 3:00 – 5:00 pm, Fairview/Kitsilano Ballrooms

Alexa Becker¹ (agb5621@psu.edu), Catherine M. Carpenter², Min Sung Seo¹, Amy A. Overman³, Nancy A. Dennis¹; ¹The Pennsylvania State University, ²University of California - Davis, ³Xavier University

Unitization is a process by which the constituents of an associative pair are posited to be encoded as a single, cohesive unit rather than a set of discrete items. Unitization enhances associative memory performance compared to traditional associative encoding, and it has been argued that this is because unitization allows item processing resources to support encoding and retrieval. This is a particularly useful strategy for older adults, as associative memory declines exist alongside relatively stable item memory capabilities in healthy aging. To this point, behavioral and neural evidence demonstrates increased recruitment of familiarity and item-based neural resources during the processing of unitized relative to non-unitized items. However, it remains unclear how unitized items directly compare to single items at the neural level. The current study employs pattern similarity analysis (PSA) to compare the neural correlates of item (single words), unitized (compound words), and non-unitized (unrelated word pairs) encoding and retrieval in a sample of healthy younger and older adults. Results suggest that, in subregions of the medial temporal lobe (MTL), unitized stimuli are processed more similarly to non-unitized stimuli than they are to single items at both encoding and retrieval. These findings suggest that, although unitization promotes integrative processing between discrete items, this does not necessarily shift their neural correlates to be more similar to that of single items than discrete pairs, and this is even the case for extremely well-unitized stimuli such as compound words.

Topic Area: LONG-TERM MEMORY: Development & aging