Biology subjects

Reagh, Z. M.

Publications and source records attributed to Reagh, Z. M..

11 recordsLinked to original sources

bioRxiv2026

Post-Learning Reactivation of Memories for Naturalistic Continuous Experiences

Memories are not static records of the past; rather, the act of remembering can change how an event is recalled. Intriguingly, several studies also suggest that memories may be reactivated during rest. However, reactivation has largely been studied for spatial tasks and discrete stimuli, and we know little about whether spontaneous reactivation occurs for long timescale naturalistic events and how reactivation affects retention. Using fMRI, we show that neural activity patterns in the hippocampus and the Default Mode Network during encoding of narrative events were spontaneously reactivated during rest. Contrary to predictions, reactivation did not strengthen recall of movie details, and instead exploratory analyses suggested that reactivation in the hippocampus was associated with more gist-like recall one week later. These findings support the idea that memories for complex events may be spontaneously reactivated, but they suggest that rather than simply strengthening episodic memories, reactivation might help transform them.

neuroscience↗

bioRxiv2026

LLM-powered automatic scoring tools for memory recall

Free recall of naturalistic stimuli, such as films and stories, reveals what people remember and how they organize it. Scoring such recall requires matching each recalled utterance to the encoded stimulus, and doing this manually often makes large studies impractical. Existing automated methods mostly return similarity or aggregate scores rather than explicit matches between recalled and stimulus content. Here we introduce an open-source, model-agnostic pipeline that uses a large language model (LLM) to divide the stimulus and the recall into information units and to match units between the two texts. The output is a table of unit-to-unit matches with accuracy labels, from which standard analysis scripts compute recall measures. We validated the pipeline with four LLMs (Claude Sonnet 4.5, GPT 5.4, Gemini 2.5 Pro, and Gemini 2.5 Flash) on three datasets. On typed recall of four short stories, agreement between each model and two trained raters ({phi} = .73-.79) was close to the agreement between the raters themselves ({phi} = .77). A second run reproduced each model's matches ({phi} = .91-.97) more closely than the raters agreed with each other. On spoken recall of 10 films, every model attributed recall to the correct film with high agreement. On uncorrected speech-to-text recall of a television episode, agreement varied more across models. The median cost was under $1 per participant for every model. These results suggest that the pipeline can serve as a reliable, low-cost alternative to manual scoring of free recall.

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bioRxiv2026

Age Differences in Hippocampal Neural Timescales During Movie-Viewing

Episodic memory requires integrating information across multiple scales, a process theorized to be supported by a gradient of neural timescales along the anterior-posterior axis of the hippocampus that enables both coarse-and fine-grained representations. Aging is associated with changes in hippocampal function and declines in fine-grained episodic memory, but whether this impacts the gradient organization of the hippocampus is unknown. Additionally, the relationship between the neural timescales of the hippocampus and memory specificity remains unclear. Here, we analyzed the length of timescales of individual voxels in the hippocampus during movie-viewing, along with subsequent recall data, in a sample of young and older participants. Younger adults showed the expected anterior-to-posterior timescale gradient, replicating prior work. In contrast, older adults exhibited a reversal of the expected gradient. Older adults recall was coarser and more gist-like than that of younger adults. In younger adults, longer neural timescales were associated with less specific, more gist-like recall; this was seen predominantly in the posterior-lateral hippocampus. In contrast, no relationship between neural timescales and recall were observed in older adults. An exploratory analysis revealed a similar relationship between neural timescales and memory specificity in cortical regions, in younger but not older adults. These findings suggest that aging alters the organization of neural activity throughout the hippocampus and that neural timescales in the hippocampus and cortex are related to the specificity of memory. Significance statementAs people age, episodic memories become more gist-like and less detailed. The hippocampus, which supports both gist and detailed memory, exhibits a neural timescale gradient--from slow-changing activity (longer timescales) to fast-changing activity (shorter timescales). This organization is theorized to support coarse-and fine-grained memory, respectively, yet a direct link to the age-related shift towards gist-like memory remains unestablished. Here, we identify an age-related shift in the hippocampal timescale gradient that parallels a decline in memory specificity. Furthermore, longer timescales in the hippocampus and cortical regions correlated with decreased memory specificity in younger adults. These findings demonstrate that aging is associated with a reorganization of hippocampal activity and that cortical timescales during encoding may relate to the specificity of memory.

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bioRxiv2025

Key moments in naturalistic events synchronize neural activity patterns and dominate memory reinstatement

Continuous experiences are experienced and remembered in terms of events that unfold over time. There is strong evidence that event boundaries segment experience during comprehension and that event representations are compressed in memory; however, this compression is poorly understood. We developed a novel storyboard paradigm to test the hypothesis that representations of continuous experiences are defined by a subset of key moments that capture the underlying narrative. Participants agreed on when key moments occurred; some key moments corresponded with event boundaries, but many did not. fMRI during encoding revealed that neural activity patterns throughout the default network synchronized across individuals at key moments. Further, comparing fMRI during encoding to fMRI during retrieval revealed that key moments are overrepresented in neural patterns that are reinstated during event recall in the posterior-medial cortex. These results suggest that continuous events are punctuated by a small subset of meaningful moments, which dominate neural representations during perception and memory.

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bioRxiv2024

Evidence for shallow cognitive maps in schizophrenia

Individuals with schizophrenia can have marked deficits in goal-directed decision making. Prominent theories differ in whether schizophrenia (SZ) affects the ability to exert cognitive control, or the motivation to exert control. An alternative explanation is that schizophrenia negatively impacts the formation of cognitive maps, the internal representations of the way the world is structured, necessary for the formation of effective action plans. That is, deficits in decision-making could also arise when goal-directed control and motivation are intact, but used to plan over ill-formed maps. Here, we test the hypothesis that individuals with SZ are impaired in the construction of cognitive maps. We combine a behavioral representational similarity analysis technique with a sequential decision-making task. This enables us to examine how relationships between choice options change when individuals with SZ and healthy age-matched controls build a cognitive map of the task structure. Our results indicate that SZ affects how people represent the structure of the task, focusing more on simpler visual features and less on abstract, higher-order, planning-relevant features. At the same time, we find that SZ were able to display similar performance on this task compared to controls, emphasizing the need for a distinction between cognitive map formation and changes in goal-directed control in understanding cognitive deficits in schizophrenia.

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bioRxiv2021

Connectome-based Modeling of Mnemonic Discrimination in Younger and Older Adults

The ability to distinguish existing memories from similar perceptual experiences is a core feature of episodic memory. This ability is often examined using the Mnemonic Similarity Task in which people discriminate memories of studied objects from perceptually similar lures. Studies of the neural basis of such mnemonic discrimination have mostly focused on hippocampal function and connectivity. However, default mode network (DMN) connectivity may also support such discrimination, given that the DMN includes the hippocampus, and its connectivity supports many aspects of episodic memory. Here, we used connectome-based predictive modeling to identify associations between intrinsic DMN connectivity and mnemonic discrimination. We leveraged a wide range of abilities across healthy younger and older adults to facilitate this predictive approach. Resting-state functional connectivity in the DMN predicted mnemonic discrimination outside the MRI scanner, especially among prefrontal and temporal regions and including several hippocampal regions. This predictive relationship was stronger for younger than older adults, primarily for temporalprefrontal connectivity. The novel associations established here are consistent with mounting evidence that broader cortical networks including the hippocampus support mnemonic discrimination. They also suggest that age-related network disruptions undermine the extent that the DMN supports this ability. This study provides the first indication of how intrinsic functional properties of the DMN support mnemonic discrimination.

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bioRxiv2021

A cortico-hippocampal scaffold for representing and recalling lifelike events

Although every life event is unique, there are considerable commonalities across events. However, little is known about whether or how the brain flexibly represents information about different event components at encoding and during remembering. Here, we show that different cortico-hippocampal networks systematically represent specific components of events depicted in videos, both during viewing and during episodic memory retrieval. Regions of an Anterior Temporal Network represented information about people, generalizing across contexts, whereas regions of a Posterior Medial Network represented context information, generalizing across people. Medial prefrontal cortex generalized across videos depicting the same schema, whereas the hippocampus maintained event-specific representations. Similar effects were seen in real-time and recall, suggesting reuse of event components across overlapping episodic memories. These findings reveal a computationally optimal strategy in cortico-hippocampal networks for encoding different high-level event components, supporting efficient reuse for event comprehension, imagination, and recollection.

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bioRxiv2020

Bridges, not walls: the hippocampus builds narrative memories across distant events

Lifes events are scattered throughout time, yet we often recall different events in the context of an integrated narrative. Prior research suggests that the hippocampus, which supports memory for past events, can sometimes support integration of overlapping associations or separate events, but the conditions which lead to hippocampus-dependent memory integration are unclear. We used functional brain imaging to test whether the ability to form a larger narrative (narrative coherence) drives hippocampal memory integration. During encoding of fictional stories, the hippocampus supported patterns of activity, including activity at boundaries between events, which were more similar between distant events that formed one coherent narrative, compared with events taken from unrelated narratives. Twenty-four hours later, the hippocampus preferentially supported detailed recall of coherent narrative events, through reinstatement of hippocampal activity patterns from encoding. These findings reveal a key function of the hippocampus: the dynamic integration of events into a narrative structure for memory.

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bioRxiv2019

Hippocampal subfields integrate information about past temporal and cognitive contexts

The hippocampus plays a critical role in supporting episodic memory, in large part by binding together experiences and items with surrounding contextual information. At present, however, little is known about the roles of different hippocampal subfields in supporting this item-context binding. To address this question, we constructed a task in which items were affiliated with differing types of context - cognitive associations that vary at the local, item level and membership in temporally organized lists that linked items together at a global level. Participants made item recognition judgments while undergoing high-resolution fMRI imaging. We performed voxel pattern similarity analyses to answer the question of how human hippocampal subfields represent retrieved information about cognitive states and the time at which a past event took place. As participants recollected previously presented items, activity patterns in the CA23DG subregion carried information about prior cognitive states associated with these items. We found no evidence to suggest reinstatement of information about temporal context at the level of list membership, but exploratory analyses revealed representations of temporal context at a coarse level in conjunction with representations of cognitive contexts. Results are consistent with characterizations of CA23DG as a critical site for binding together items and contexts in the service of memory retrieval.

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bioRxiv2017

The ANTs Longitudinal Cortical Thickness Pipeline

Longitudinal studies of development and disease in the human brain have motivated the acquisition of large neuroimaging data sets and the concomitant development of robust methodological and statistical tools for quantifying neurostructural changes. Longitudinal-specific strategies for acquisition and processing have potentially significant benefits including more consistent estimates of intra-subject measurements while retaining predictive power. In this work, we introduce the open-source Advanced Normalization Tools (ANTs) registration-based cortical thickness longitudinal processing pipeline and its application to the first phase of the Alzheimers Disease Neuroimaging Initiative (ADNI-1) comprising over 600 subjects with multiple time points from baseline to 36 months. We demonstrate in these data that the single-subject template construction and same orientation processing results in a simultaneous minimization of residual variability and maximization of between-subject variability immediately estimable from a longitudinal mixed-effects modeling strategy. It is known from the statistical literature that optimizing these dual criteria leads to greater scientific interpretability in terms of tighter confidence intervals in calculated mean trends, smaller prediction intervals, and narrower confidence intervals for determining cross-sectional effects. This strategy is evaluated over the entire cortex, as defined by the Desikan-Killiany-Tourville labeling protocol, where comparisons are made with the cross-sectional and longitudinal FreeSurfer processing streams. Subsequent linear mixed effects modeling for identifying diagnostic groupings within the ADNI cohort is provided as supporting evidence for the utility of the proposed ANTs longitudinal framework which provides unbiased structural neuroimage processing and competitive to superior power for longitudinal structural change detection.

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bioRxiv2017

Anterolateral entorhinal-hippocampal imbalance in older adults disrupts object pattern separation

The entorhinal cortex (EC) is among the earliest brain areas to deteriorate in Alzheimers disease (AD). However, the extent to which functional properties of the EC are altered in the aging brain, even in the absence of clinical symptoms, is not understood. Recent human fMRI studies have identified a functional dissociation within the EC, similar to what is found in rodents. Here, we used high-resolution fMRI to identify a specific hypoactivity in the anterolateral EC (alEC) commensurate with major behavioral deficits on an object pattern separation task in asymptomatic older adults. Only subtle deficits were found in a comparable spatial condition, with no associated differences in posteromedial EC between young and older adults. We additionally link this condition to previously reported dentate/CA3 hyperactivity, both of which were associated with object mnemonic discrimination impairment. These results provide novel evidence of alEC-dentate/CA3 circuit dysfunction in cognitively normal aged humans.

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