Biology subjects

Dennis, N. A.

Publications and source records attributed to Dennis, N. A..

8 recordsLinked to original sources

bioRxiv2026

Spatially unitized associations occupy an intermediate position along the item-to-association continuum in older adults

Older adults show disproportionate impairments in associative memory relative to memory for individual items. Unitization, the process by which discrete elements are encoded as a single integrated representation, has been proposed to mitigate this deficit by reducing reliance on hippocampal binding and shifting processing toward perirhinal cortex-mediated item-based encoding. However, most prior work has not included a single item baseline, leaving unclear whether unitized associations are truly processed like items. Here, we investigated whether spatial proximity supports associative memory in older adults and how this benefit is reflected in medial temporal lobe (MTL) encoding activity. Participants encoded unrelated object pairs presented either proximally (spatially integrated) or distally (spatially separated), alongside a single item condition. Behaviorally, older adults showed better memory for proximal than distal pairs, though performance remained below that of single items. Neurally, MTL activity scaled with associative demand, with hippocampal activity increasing and perirhinal activity decreasing as demand increased. Results further revealed an anterior-posterior MTL dissociation, with proximal pairs sharing neural properties with both single items and distal pairs without uniquely recruiting either. Furthermore, hippocampal patterns reliably distinguished item from associative encoding, and the parahippocampal cortex discriminated all three conditions, indicating that the item-associative structure of the MTL was preserved in aging. Together, these findings suggest that proximal pairs occupy an intermediate position between item and associative representations within an intact MTL architecture, and that spatial proximity benefits associative memory in older adults by partially, but not fully, shifting associative demands toward item-based processing. HighlightsO_LISpatial proximity improved associative memory in older adults. C_LIO_LIHippocampal and PRC activity scaled with associative binding demands. C_LIO_LISpatially unitized associations fell between single items and distal associations in MTL encoding activity. C_LIO_LIMTL item-association functional structure was preserved in older adults. C_LI

neuroscience↗

bioRxiv2026

Temporal Interference Modulates Medial Temporal and Frontoparietal Activity During Mnemonic Discrimination: A high-resolution whole-brain fMRI investigation

Mnemonic discrimination--the ability to distinguish between existing memories and similar new inputs--supports accurate memory in the face of interference (e.g., remembering where you parked today versus yesterday in the same parking deck). Although hippocampal pattern separation has been emphasized as a key mechanism, recent theoretical frameworks and empirical findings suggest that surrounding medial temporal lobe and cortical regions also contribute by resolving interference. An important source of interference in everyday life is temporal interference: similar events may compete not only because they overlap perceptually, but also because they are separated by intervening experiences (e.g., having to remember your morning parking spot after a full day of work). Here, we investigated how temporal interference impacts mnemonic discrimination and its neural correlates using high-resolution fMRI and a continuous recognition task in which the lag between an items first presentation and its subsequent target or similar lure was systematically manipulated (10, 60, or 140 intervening trials). Behaviorally, increasing lag impaired both mnemonic discrimination and target recognition. At the neural level, lag effects were not observed in hippocampal subfields. Rather, temporal interference modulated activity in extrahippocampal MTL regions including parahippocampal and perirhinal cortex, as well as distributed cortical regions including frontoparietal control areas. Importantly, lag-related modulation was process-specific, with partially dissociable patterns for successful mnemonic discrimination and target recognition. Together, these findings demonstrate that temporal interference engages a distributed MTL-cortical network that supports interference resolution during mnemonic discrimination.

neuroscience↗

bioRxiv2023

Neural similarity of schematic information overrides new information, regardless of target or lure information

Schemas allow us to make assumptions about the world based upon previous experiences and aid in memory organization and retrieval. However, a reliance on schemas may also result in increased false memories to schematically related lures. Prior neuroimaging work has linked schematic processing in memory tasks to activity in prefrontal, visual, and temporal regions. Yet, it is unclear what type of processing in these regions underlies memory errors. The current study examined where schematic lures exhibit greater neural similarity to schematic targets, leading to this memory error, as compared to neural overlap with non-schematic lures, which, like schematic lures, are novel items at retrieval. Results showed that patterns of neural activity in ventromedial prefrontal cortex, medial frontal gyrus, middle temporal gyrus, hippocampus, and occipital cortices exhibited greater neural pattern similarity for schematic targets and schematic lures than between schematic lures and non-schematic lures. As such, results suggest that schematic membership, and not object history, may be more critical to the neural processes underlying memory retrieval in the context of a strong schema.

neuroscience↗

bioRxiv2022

Neural distinctiveness and discriminability in core network representations support associative unitization

Previous work has suggested unitized pairs behave as a single unit and more critically, are processed neurally different than those of associative memories. The current works examines the neural differences between unitization and non-unitized memory using fMRI and multivoxel analyses. Specifically, we examined the differences across face-occupation pairings as a function of whether the pairing was viewed as a person performing the given job (unitized binding) or a person saying they knew someone who had a particular job (non-unitized binding). The results show that at encoding, the angular gyrus can discriminate between unitized and non-unitized target trials. Additionally, during encoding, the medial temporal lobe (hippocampus and perirhinal cortex), frontal parietal regions (angular gyrus and medial frontal gyrus) and visual regions (middle occipital cortex) exhibit distinct neural patterns to recollected unitized and non-unitized targets. Furthermore, the medial frontal gyrus and middle occipital cortex show greater neural similarity for recollected unitized trials than those of recollected non-unitized trials. We conclude that visually unitized pairs may enhance unitization in older adults due to greater similarity of trials within the same condition during the encoding process.

neuroscience↗

bioRxiv2022

Investigation of the neural effects of memory training to reduce false memories in older adults: Univariate and multivariate analyses

The growing population of older adults emphasizes the need to develop interventions that prevent or delay some of the cognitive decline that accompanies aging. In particular, as memory impairment is the foremost cognitive deficit affecting older adults, it is vital to develop interventions that improve memory function. This study addressed the problem of false memories in aging by training older adults to use details of past events during memory retrieval to distinguish targets from related lures. We examined the neural basis of a retrieval-based monitoring strategy by assessing changes in univariate BOLD activity and discriminability of targets and lures pre and post training. Results showed training-related decreases in false memory rates with no alterations to hit rates. Training and practice were associated with altered recruitment of a frontoparietal monitoring network as well as benefits to neural discriminability within network regions. Participants with lower baseline neural discriminability between target and lure items exhibited the largest changes in neural discriminability. Collectively, our results highlight the benefits of training for reductions of false memories in aging. They also provide an understanding of the neural mechanisms that support these reductions.

neuroscience↗

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↗

bioRxiv2021

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

Typical aging is associated with increases in false memory rates among older adults. Such errors are frequently associated with differential neural activity during encoding and retrieval in older compared to younger adults within visual cortices, hippocampus, and front-parietal regions. It remains unknown how pattern similarity reductions relate to false memories in healthy aging. Using encoding-retrieval similarity (ERS) analyses in a sample of younger and older adults, we examined how the similarity of neural patterns between memory phases associated with target and lure objects was impacted by age and contributed to false memory rates. Single-item ERS for targets and lures was reduced by age throughout much of the ventral visual stream and the posterior hippocampus. Furthermore, ERS associated with perceptual lures within the visual stream maintained differential relationships with false memory. Finally, a global ERS metric accounted for age deficits in single-item ERS, but did not contribute to false memory rates. These findings highlight the contribution of age-related reductions in ERS across multiple representational levels to false memories in healthy aging.

neuroscience↗