Biology subjects

Ellmore, T. M.

Publications and source records attributed to Ellmore, T. M..

8 recordsLinked to original sources

bioRxiv2025

Linking White Matter Integrity to Recognition Memory Speed: Fixel-Based and Fornix Analyses in Young to Middle Adulthood

Age-related differences in white matter structure are increasingly understood as nonlinear, regionally specific, and behaviorally relevant. Using whole-brain fixel-based analysis (FBA), we examined how recognition memory speed relates to micro- and macrostructural white matter properties across a sample spanning young to middle adulthood. Slower response times were associated with higher fiber density (FD) in left frontoparietal tracts, nonlinear increases in fiber cross-section (log(FC)) in the anterior corpus callosum, and elevated combined fiber density and cross-section (FDC) in posterior callosal and cingulum pathways. These associations were most pronounced among individuals in the later decades of this age range, suggesting that white matter morphology reflects both extended maturation and emerging age-related decline. In a separate, hypothesis-driven analysis, we applied deterministic tractography to reconstruct the fornix and extracted mean fractional anisotropy (FA) along its length. Greater fornix FA and younger age together explained 34% of the variance in retrieval speed. These findings highlight regionally distinct structural contributions to memory performance and support lifespan models emphasizing individual variability and neuroplasticity in white matter development. This integrative approach underscores the value of combining whole-brain and tract-specific analyses to advance our understanding of white matter contributions to cognitive aging. HighlightsO_LISlower RT linked to higher fiber density in left frontoparietal white matter C_LIO_LISlower RT associated with nonlinear increases in anterior corpus callosum log(FC) C_LIO_LIFDC increased in posterior callosal and cingulum tracts in slower older adults C_LIO_LIFindings support prolonged maturation and regionally specific age-related decline C_LIO_LIFornix FA and age explained 34% of variance in memory retrieval speed C_LI

neuroscience↗

bioRxiv2021

Interhemispheric Connectivity Supports Load-Dependent Working Memory Maintenance for Complex Visual Stimuli

A critical manipulation used to study the neural basis of working memory (WM) is to vary the information load at encoding followed by measurements of activity and connectivity during maintenance in the subsequent delay period. The hallmark finding is that delay period activity and connectivity increases between frontal and parietal brain regions as load is increased. Most WM studies, however, employ simple stimuli (e.g., simple shapes or letters) during encoding and utilize unfilled intervals (e.g., a blank screen or fixation cross) during the delays. In the present study, we asked how delay period activity and connectivity change during low and high load maintenance of complex stimuli. Twenty-two participants completed a modified Sternberg WM task with two or five naturalistic scenes as stimuli while scalp EEG was recorded. In each trial, the delay interval was filled with phase scrambled scenes to provide a visual perceptual control with color and spatial frequency similar to the non-scrambled scenes presented during encoding. The results showed that theta and alpha delay activity amplitude was reduced during high compared to low WM load across frontal, central, and parietal sources. Functional connectivity during the delay was assessed by phase-locking value (PLV) and revealed a network with higher connectivity during low WM load consisting of increased PLV between 1) left frontal and right posterior temporal sources in the theta and alpha bands, 2) right anterior temporal and left central sources in the alpha and lower beta bands, and 3) left anterior temporal and posterior temporal sources in the theta, alpha, and lower beta bands. These findings demonstrate a role for interhemispheric connectivity during WM maintenance of complex stimuli. We discuss significance with respect to allocation of limited attentional resources and the filtering of interference.

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bioRxiv2021

Spontaneous Eye Blink Rate during the Working Memory Delay Period Predicts Task Performance

Spontaneous eye blink rate (sEBR) has been linked to attention and memory, specifically working memory (WM). sEBR is also related to striatal dopamine (DA) activity with schizophrenia and Parkinsons disease showing increases and decreases respectively in sEBR. A weakness of past studies of sEBR and WM is that correlations have been reported using blink rates taken at baseline either before or after performance of the tasks used to assess WM. The goal of the present study was to understand how fluctuations in sEBR during different phases of a visual WM task predict task accuracy. In two experiments, with recordings of sEBR collected inside and outside of a magnetic resonance imaging bore, we observed sEBR to be positively correlated with WM task accuracy during the WM delay period. We also found task-related modulation of sEBR, including higher sEBR during the delay period compared to rest, and lower sEBR during task phases (e.g., stimulus encoding) that place demands on visual attention. These results provide further evidence that sEBR could be an important predictor of WM task performance with the changes during the delay period suggesting a role in WM maintenance. The relationship of sEBR to DA activity and WM maintenance is discussed.

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bioRxiv2020

A Simultaneous EEG-fMRI Study of Thalamic Load-Dependent Working Memory Delay Period Activity

Working memory (WM) is an essential component of executive functions which depend on maintaining task-related information online for brief periods in both the presence and absence of interfering stimuli. Active maintenance occurs during the WM delay period, the time between stimulus encoding and subsequent retrieval. Previous studies have extensively documented prefrontal (PFC) and posterior parietal (PPC) cortex activity during the WM delay period, but the role of subcortical structures including the thalamus remains to be fully elucidated, especially in humans. Using simultaneous EEG-fMRI, we investigated the role of the thalamus during the WM delay period following low and high memory load encoding. During the delay, participants passively viewed scrambled images containing similar color and spatial frequency to serve as a perceptual baseline. Using individual fMRI-weighted source analyses centered around delay period onset, the effects of increased and decreased memory load on maintenance were observed bilaterally in thalamus with higher source activity evoked during low compared to high load maintenance. The main finding that thalamic activation was attenuated during high compared to low load maintenance suggesting a sensory filtering role for thalamus during consolidation of stimuli in WM where the highest evoked activity occurs when fewer stimuli need to be maintained in the presence of interfering perceptual stimuli during the delay. The results support the idea that the thalamus plays a role in short-term memory maintenance by regulating processing of interfering stimuli.

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bioRxiv2019

Does rehearsal benefit visual memory? The role of semantic associations in the maintenance of intact and phase scrambled scenes.

Rehearsal during working memory (WM) maintenance facilitates retrieval. Less is known about how rehearsal modulates WM delay activity. In the present study, 44 participants completed a Sternberg Task with either intact novel scenes or phase-scrambled scenes, which had similar color and spatial frequency but lacked semantic content. During each condition participants generated a descriptive label and covertly rehearsed or suppressed (repeated "the") during the delay. This was easy in the former but more difficult in the later condition where scenes lacked semantic content. Behavioral performance and EEG delay activity was analyzed as a function of maintenance strategy. Performance during WM revealed a benefit of rehearsal for phase-scrambled but not intact scenes. Examination of the absolute amplitude revealed three underlying sources of activity for rehearsal, including the left anterior temporal (TAL), left and midline parietal regions. Increases in alpha and theta activity in TAL were correlated with improvement in performance on WM with rehearsal only when labeling was not automatic (i.e. phase-scrambled scenes), which may reflect differences in labeling and rehearsal (i.e. semantic associations vs. shallow labels). We conclude that rehearsal only benefits memory for visual stimuli that lack semantic information, and that this is correlated with changes in alpha and theta rhythms.

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bioRxiv2018

Saccades and Handedness Interact to Affect Scene Memory

Repetitive saccades benefit memory when executed before retrieval, with greatest effects for episodic memory in consistent-handers. Questions remain including how saccades affect scene memory, an important visual component of episodic memory. The present study tested how repetitive saccades affect working and recognition memory for novel scenes. Handedness direction (left-right) and degree (strong/consistent vs. mixed/inconsistent) was measured by raw and absolute laterality quotients respectively from an 8-question handedness inventory completed by 111 adults. Each then performed either 30 seconds of repetitive horizontal saccades or fixation before or after tasks of scene working memory and scene recognition. Regression with criterion variables of overall percent correct accuracy and d-prime sensitivity showed that when saccades were made before working memory, there was better overall accuracy as a function of increased direction but not degree of handedness. Subjects who made saccades before working memory also performed worse during subsequent recognition memory, while subjects who fixated or made saccades after the working memory task performed better. Saccades made before recognition resulted in recognition accuracy that was better (Cohens d=0.3729), but not significantly different from fixation before recognition. The results demonstrate saccades and handedness interact to affect scene memory with larger effects on encoding than recognition. Saccades before scene encoding in working memory are detrimental to short- and long-term memory, especially for those who are not consistently right-handed, while saccade execution before scene recognition does not appear to benefit recognition accuracy. The findings are discussed with respect to theories of interhemispheric interaction and control of visuospatial attention.

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bioRxiv2017

Visual Continuous Recognition Reveals Widespread Cortical Contributions to Scene Memory

Humans have a remarkably high capacity and long duration memory for complex scenes. Previous research documents the neural substrates that allow for efficient categorization of scenes from other complex stimuli like objects and faces, but the spatiotemporal neural dynamics underlying scene memory are less well understood. In the present study, we used high density EEG during a visual continuous recognition task in which new, old, and scrambled scenes consisting of color outdoor photographs were presented at an average rate 0.26 Hz. Old scenes were single repeated presentations occurring within either a short-term ([≤] 20 seconds) or longer-term intervals of between 30 sec and 3 minutes or 4 and 10 minutes. Overall recognition was far above chance, with better performance at short- than longer-term intervals. A group ANOVA found parietal and frontal ERPs discriminated the three scene types as early as 59 ms after stimulus onset. Parietal ERPs were greater for old compared to new scenes by 189 ms, while fronto-temporal ERPs were greater for new compared to old scenes by 194 ms. For old scenes presented within longer-term intervals, parieto-temporal and centro-frontal ERPs were greater by 228 and 355 ms respectively compared to old scenes presented within a short-term interval. Supervised machine learning exhibited above-chance decoding of scene type by 275 ms. Single-subject BOLD-fMRI showed greater activity for old scenes across frontal, parietal, and temporal cortex. These converging findings show that a widespread network including parietal, frontal, and temporal regions supports short- and long-term scene memory.\n\nSignificance StatementThe ability to recognize a scene as novel or familiar is critical for basic cognition. Scene recognition plays an important role in episodic memory because it helps us quickly establish place, a first step in recalling where previous events occurred. Short-term recognition supports our ability to detect changes in the immediate environment, an ability critical to survival. Scene recognition after a longer-term interval is often the essential cue for retrieving autobiographical memories. Previous behavioral studies demonstrate high capacity and long duration scene memory. Neural studies have identified the brain regions that support scene-specific processing. The present study extends this research by filling a gap in understanding how distributed spatiotemporal patterns of neural activity support short- and long-term scene memory.

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bioRxiv2017

Early And Late Components Of EEG Delay Activity Correlate Differently With Scene Working Memory Performance

Sustained and elevated activity during the working memory delay period has long been considered the primary neural correlate for maintaining information over short time intervals. This idea has recently been reinterpreted in light of findings generated from multiple neural recording modalities and levels of analysis. To further investigate the sustained or transient nature of activity, the temporal-spectral evolution (TSE) of delay period activity was examined in humans with high density EEG during performance of a Sternberg working memory paradigm with a relatively long six second delay and with novel scenes as stimuli. Multiple analyses were conducted using different trial window durations and different baseline periods for TSE computation. Sensor level analyses revealed transient rather than sustained activity during delay periods. Specifically, the consistent finding among the analyses was that high amplitude activity encompassing the theta range was found early in the first three seconds of the delay period. These increases in activity early in the delay period correlated positively with subsequent ability to distinguish new from old probe scenes. Source level signal estimation implicated a right parietal region of transient early delay activity that correlated positively with working memory ability. This pattern of results adds to recent evidence that transient rather than sustained delay period activity supports visual working memory performance. The findings are discussed in relation to synchronous and desynchronous intra- and inter-regional neural transmission, and choosing an optimal baseline for expressing temporal-spectral delay activity change.

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