Gerver, C. R. | bioRxiv Science

bioRxiv2022

Neural Distinctiveness and Reinstatement of Hippocampal Representations Support Unitization for Associations

The medial temporal lobe (MTL) is critical to associative memory success. Yet not all types of associations may be processed in a similar manner within MTL subregions. In particular, work suggests that intra- and inter-item associations not only exhibit differences in overall rates of recollection, but also recruit different MTL subregions. Whereas intra-item associations, akin to unitization, take advantage of associations between within-item features, inter-item associations form links across discrete items. The current work aimed to examine the neural differences between these two types of associations using multivariate neural analyses. Specifically, the current study examined differences across face-occupation as a function of whether the pairing was viewed as a person performing the given job (intra-item binding) or a person saying that they knew someone who had a particular job (inter-item binding). The results show that at encoding, successfully recollected intra- and inter-item associations are discriminable from one another in the hippocampus, parahippocampal cortex, and perirhinal cortex. Additionally, the two trial types are reinstated distinctly such that inter-item trials have higher neural reinstatement from encoding to retrieval compared to intra-item trials in the hippocampus. We conclude that intra- and inter-associative pairs may utilize similar neural regions that represent patterns of activation differentially at encoding. However, in order to reinstate information to the same degree (i.e., subsequently successfully recollected) inter-item associations may act in a compensatory manner, while it is not necessary for intra-item associations to be reinstated to the same degree. This may indicate that intra-item associations promote more efficient reinstatement.

neuroscience↗

bioRxiv2021

Understanding associative false memories in aging using multivariate analyses

Age-related declines in associative memory are ubiquitous, having been observed across a wide array of stimuli and experimental paradigms. Research further shows that such decreases in behavioral discriminability arise from increases in false memories for recombined lures. The current study examined the underlying neural basis of associative false memories by using representational similarity analyses to examine both age differences in the reactivation of encoded representations during retrieval and the neural overlap in the similarity of neural patterns underlying targets and related lures during retrieval. Behaviorally, we observed an age-related reduction in d, which was shown to be driven by increased false alarms in the older adults. While we found no age difference in the relationship between patterns of neural activity underlying hits across memory phases (as measured by ERS), the similarity of neural patterns underlying targets and lures was affected by age. Specifically, while younger and older adults exhibited overall higher pattern similarity between hits and CRs compared to hits and FAs (as measured by RSA), this difference was reduced in older adults within occipital cortices. Additionally, greater Hit-FA representational similarity correlated with increases in associative FAs across occipital, frontal, and parietal cortices. Results suggest that while neural representations underlying targets may not differ across age, greater pattern similarity between the neural representation of targets and lures may reflect reduced distinctiveness of the information encoded in memory, such that old and new items are more difficult to discriminate, leading to more false alarms.

neuroscience↗