Hippocampal and cortical mechanisms at retrieval explain variability in episodic remembering in older adults

Abstract

Age-related episodic memory decline is characterized by striking heterogeneity across individuals. Hippocampal pattern completion is a fundamental process supporting episodic memory. Yet, the degree to which this mechanism is impaired with age, and contributes to variability in episodic memory, remains unclear. We combine univariate and multivariate analyses of fMRI data from a large cohort of cognitively normal older adults (N=100) to measure hippocampal activity and cortical reinstatement during retrieval of trial-unique associations. Trial-wise analyses revealed that (a) hippocampal activity scaled with reinstatement strength, (b) cortical reinstatement partially mediated the relationship between hippocampal activity and associative retrieval, (c) older age weakened cortical reinstatement and its relationship to memory behaviour. Moreover, individual differences in the strength of hippocampal activity and cortical reinstatement explained unique variance in performance across multiple assays of episodic memory. These results indicate that fMRI indices of hippocampal pattern completion explain within- and across-individual memory variability in older adults.

Age-related differences in encoding-retrieval similarity and their relationship to false memory

“…Specifically, both single-item and set-level ERS was associated with successful remembering within the ventral visual stream and frontal cortices (Ritchie et al 2013). This finding is supported a more recent study by Trelle et al (2020) who also found that ventral temporal cortex ERS was predictive of veridical memory retrieval. Accordingly, research suggests that the similarity in neural patterns within ventral visual cortices across memory phases play a critical role in memory success in younger adults.…”

“…For example, it is possible that older adults do not store, and thus do not have available as many or as high-quality, encoding-related details for retrieval compared to their younger counterparts (Dennis, Bowman, et al, 2014;Hill et al, 2021). It is also possible that older adults have such details stored in their memory, but fail to reactivate these memory traces at the time of retrieval (Trelle et al, 2020;Naspi et al, 2021). Either possibility would result in overall reduce similarity between neural patterns within occipital cortices across encoding and retrieval.…”

A Multivariate Assessment of Age-Related Cognitive Impairment in Octodon degus

“…In this study, the older participants showed a weaker communication of brain areas when compared with those used by the younger ones; however, the former recruited different brain areas to compensate (McIntosh et al, 1999 ; Cabeza et al, 2002 ). These effects are attributed to some class of compensatory activity, supporting some reorganization of the aged brain that leads to “younger” cognitive abilities (Ming and Song, 2005 ; Glisky, 2007 ; Trelle et al, 2020 ; Katsumi et al, 2021 ).…”

Functional Connectivity during Encoding Predicts Individual Differences in Long-Term Memory

“…Why is this the case? Previous work has investigated how specific neural measures, mostly involving the hippocampus or cortico-hippocampus networks, are correlated with trait-level variations in various forms of LTM (e.g., semantic and topographic memory: Trelle et al, 2020;Sormaz et al, 2017; associative memory: Touroutoglou, Andreano, Barrett, & Dickerson, 2015; free recall: Wang et al, 2010;autobiographical memory: Sheldon, Farb, Palombo, & Levine, 2016; source memory: Sneve et al, 2017). Moving beyond correlation-based analysis, recent work has started to conduct out-of-sample prediction of individual differences in LTM (e.g., reading recall: Jangraw et al, 2018; item memory and spatial memory: Persson, Stening, Nordin, & Söderlund, 2018).…”