Lifespan Age Differences in Memory Representations (LIME)
(Concluding Report)
Research Scientists
Myriam C. Sander (Project Leader, until 08/2024)
Claire Pauley (until 03/2024)
Adult Age Differences in Oscillatory Mechanisms at Encoding and Retrieval
Reductions in Representational Distinctiveness in Old Age
Summary
The LIME project investigated mechanisms of memory formation, consolidation, and retrieval, focusing on how these processes change across the lifespan. In particular, the project examined (a) whether normal cognitive aging affects oscillatory mechanisms during encoding and retrieval; and (b) whether reductions in the distinctiveness of neural representations contribute to memory decline in later adulthood. Addressing these questions requires the integration of concepts and methods from lifespan psychology, cognitive psychology, and computational neuroscience, and the development of sensitive tools to quantify representational quality across different age groups, such as EEG-based representational-similarity approaches.
The project was partially funded as a Minerva Research Group awarded to Myriam C. Sander. It was concluded in August 2024.
Adult Age Differences in Oscillatory Mechanisms at Encoding and Retrieval
Neural oscillations regulate the temporal coordination of processing in the human brain. In particular, desynchronization in the alpha/beta frequency band is known to facilitate memory formation in young adults, but its relevance among healthy older adults has not been clear. Our earlier work has shown that alpha/beta desynchronization remains predictive of successful encoding in older age but is less pronounced and accompanied by lower memory performance. Similar age differences were observed during memory retrieval, indicating that weakened desynchronization contributes to less detailed memory representations in older adults.
A second oscillatory mechanism, theta–gamma coupling, supports the construction of coherent memory representations through associative binding. The project's earlier work has shown that successful formation of associations depends on gamma activity aligning to an optimal phase of the theta rhythm (Karlsson et al., 2022). Specifically, we observed a temporal shift and greater variability in the phase relationship among older adults, paralleling their compromised associative memory performance. These results show that less precise theta–gamma coupling impedes the establishment of well-integrated memory representations in old age.
Reductions in Representational Distinctiveness in Old Age
From its inception in 2016, LIME also addressed the question whether memories are represented differently in older than in younger adults. According to the dedifferentiation hypothesis (Li et al., 2001), age-related cognitive decline reflects reduced distinctiveness of neural representations. While earlier studies had demonstrated that differences between categories, such as between faces and houses, are indeed represented less distinctively in older adults than in younger adults, questions regarding within-category distinctiveness, links to cognitive performance, and the role of retrieval processes had rarely been examined.
Using functional magnetic resonance imaging (fMRI) pattern-similarity analyses, we first demonstrated that age differences in the distinctiveness of neural representations are neither restricted to a specific cortical region nor to a specific memory stage: Distinctiveness was reduced in occipital and ventral visual regions in older adults across all memory stages—encoding, retrieval, and reinstatement. Encoding distinctiveness predicted memory success within individuals (i.e., from trial to trial) as well as between individuals. Importantly, age differences at retrieval largely mirrored those observed during encoding (Pauley & Sander, 2025). Thus, encoding quality emerged as a main determinant of later remembering.
Focusing on the open question of item versus category dedifferentation, Pauley, Karlsson, and Sander (2024) found that both item- and category-level distinctiveness are reduced in older adults relative to younger adults in early visual cortex (see Figure 1). At the same time, older adults displayed greater distinctiveness in posterior parietal cortex, possibly indicating a shift toward more abstract or semantic coding. Together, these findings show that normal cognitive aging is associated with a process of dedifferentiation at multiple representational levels that spans the full memory cycle and impairs memory performance.
Summary
Overall, the LIME project has provided a comprehensive account of how aging alters the distinctiveness and temporal dynamics of memory representations. Three major conclusions emerged: (1) memory distinctiveness at encoding is a pivotal determinant of later remembering; (2) aging-induced representational dedifferentation occurs at multiple hierarchical levels; and (3) reductions in alpha/beta desynchronization and theta-gamma coupling constitute fundamental neural mechanisms underlying changes in memory formation and retrieval. By integrating behavioral, structural, and electrophysiological evidence, LIME has established robust methodological and conceptual foundations for studying memory as a process of representational precision across the lifespan (Pauley & Sander, 2025).
Key References