Browsing by Author "Rugg, Michael D."
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Item Age-Related Differences in Prestimulus Subsequent Memory Effects Assessed with Event-Related Potentials(MIT Press Journals) Koen, Joshua D.; Horne, Erin D.; Hauck, Nedra; Rugg, Michael D.; Koen, Joshua D.; Horne, Erin D.; Hauck, Nedra; Rugg, Michael D.; 0000 0001 1596 5452 (Rugg, MD)Prestimulus subsequent memory effects (preSMEs)-differences in neural activity elicited by a task cue at encoding that are predictive of later memory performance-are thought to reflect differential engagement of preparatory processes that benefit episodic memory encoding. We investigated age differences in preSMEs indexed by differences in ERP amplitude just before the onset of a study item. Young and older adults incidentally encoded words for a subsequent memory test. Each study word was preceded by a task cue that signaled a judgment to perform on the word. Words were presented for either a short (300 msec) or long (1000 msec) duration with the aim of placing differential benefits on engaging preparatory processes initiated by the task cue. ERPs associated with subsequent successful and unsuccessful recollection, operationalized here by source memory accuracy, were estimated time-locked to the onset of the task cue. In a late time window (1000-2000 msec after onset of the cue), young adults demonstrated frontally distributed preSMEs for both the short and long study durations, albeit with opposite polarities in the two conditions. This finding suggests that preSMEs in young adults are sensitive to perceived task demands. Although older adults showed no evidence of preSMEs in the same late time window, significant preSMEs were observed in an earlier time window (500-1000 msec) that was invariant with study duration. These results are broadly consistent with the proposal that older adults differ from their younger counterparts in how they engage preparatory processes during memory encoding.Item Anterior Thalamic High Frequency Band Activity Is Coupled with Theta Oscillations at Rest(Frontiers Media S.A.) Sweeney-Reed, Catherine M.; Zaehle, Tino; Voges, Juergen; Schmitt, Friedhelm C.; Buentjen, Lars; Borchardt, Viola; Walter, Martin; Hinrichs, Hermann; Heinze, Hans-Jochen; Rugg, Michael D.; Knight, Robert T.; Rugg, Michael D.Cross-frequency coupling (CFC) between slow and fast brain rhythms, in the form of phase-amplitude coupling (PAC), is proposed to enable the coordination of neural oscillatory activity required for cognitive processing. PAC has been identified in the neocortex and mesial temporal regions, varying according to the cognitive task being performed and also at rest. PAC has also been observed in the anterior thalamic nucleus (ATN) during memory processing. The thalamus is active during the resting state and has been proposed to be involved in switching between task-free cognitive states such as rest, in which attention is internally-focused, and externally-focused cognitive states, in which an individual engages with environmental stimuli. It is unknown whether PAC is an ongoing phenomenon during the resting state in the ATN, which is modulated during different cognitive states, or whether it only arises during the performance of specific tasks. We analyzed electrophysiological recordings of ATN activity during rest from seven patients who received thalamic electrodes implanted for treatment of pharmacoresistant focal epilepsy. PAC was identified between theta (4-6 Hz) phase and high frequency band (80-150 Hz) amplitude during rest in all seven patients, which diminished during engagement in tasks involving an external focus of attention. The findings are consistent with the proposal that theta-gamma coupling in the ATN is an ongoing phenomenon, which is modulated by task performance.Item Comparison of the Neural Correlates of Encoding Item-Item and Item-Context AssociationsWong, Jenny X.; de Chastelaine, Marianne; Rugg, Michael D.; 0000 0001 1596 5452 (Rugg, MD); 92008261 (Rugg)fMRI was employed to investigate the role of the left inferior frontal gyrus (LIFG) in the encoding of item-item and item-context associations. On each of a series of study trials subjects viewed a picture that was presented either to the left or right of fixation, along with a subsequently presented word that appeared at fixation. Memory was tested in a subsequent memory test that took place outside of the scanner. On each test trial one of two forced choice judgments was required. For the associative test, subjects chose between the word paired with the picture at study and a word studied on a different trial. For the source test, the judgment was whether the picture had been presented on the left or right. Successful encoding of associative information was accompanied by subsequent memory effects in several cortical regions, including much of the LIFG. By contrast, successful source encoding was selectively associated with a subsequent memory effect in right fusiform cortex. The finding that the LIFG was enhanced during successful associative, but not source, encoding is interpreted in light of the proposal that subsequent memory effects are localized to cortical regions engaged by the on-line demands of the study task.;Item Effects of Transcranial Magnetic Stimulation on Individual Functional Brain Networks(2022-12-01T06:00:00.000) Agres, Phillip Frederick 1990-; Wig, Gagan; Rodrigue, Karen; Kennedy, Kristen; Hart Jr., John; Rugg, Michael D.Transcranial magnetic stimulation (TMS) has long been utilized as a tool to non-invasively study the association between brain function and cognition and is increasingly being used as a therapeutic intervention to modify brain function in an effort to treat disease. Towards these goals, recent efforts have strived to target and modify large-scale functional brain networks. This work is predicated on observations that the organization of the human functional brain network is related to behavioral performance among individuals across the lifespan, and cognitive decline that has been observed in health aging and in disease states. Large-scale brain networks consist of nodes (brain areas) that vary in their functional characteristics. Nodes belong to distinct subnetworks that represent functional brain systems related to cognition and sensory-motor function. Functional brain network organization has been observed to differ in specific topography and localization across individuals, which motivates efforts towards identifying individual-specific stimulation targets to reduce group-level bias and inaccuracies. This dissertation project utilized resting-state functional correlations (RSFC) to map the functional brain networks of individuals and identify specific stimulation targets in a group of healthy young adult participants (N = 17[9F], 18-30y). RSFC MRI was collected at baseline and 24 hours after completing a 5-day high-frequency rTMS protocol. For each individual participant, two cortical stimulation targets with distinct functional and topological properties were identified: the left angular gyrus (L. Ang.) and left middle frontal gyrus (L. MFG), with each target serving as an active control condition for the other target. On-target stimulation of each cortical target resulted in RSFC changes between the respective target node and its connections in the network, whereas RSFC changes were less evident following off-target (control-site) stimulation. RSFC changes were demonstrated to be related to the baseline RSFC strength and Euclidean distance between each target and their respective network connections, and was also related to on-target stimulation, demonstrating distal impacts of TMS that are mediated by both functional and anatomical features of functionally connected brain regions. On-target TMS to the L. Ang. decreased RSFC within the default-mode system (DMN) and on-target TMS to the L. MFG decreased RSFC within the frontoparietal control system (FPN) as well as in the default- mode system; off-target control stimulation had no impact on RSFC within the DMN. While node-level and system-level correlations were modified as a result of TMS, system segregation, an overall measure quantifying brain network organization was not impacted by TMS, highlighting the potential resiliency of a segregated brain network in the face of TMS perturbation. Notably, measures of episodic memory performance (but also fluid ability and working memory) were not impacted by TMS and were not related to observed changes in RSFC, despite previous reports that have provided evidence for these effects. This dissertation provides evidence that individualized on-target TMS modifies RSFC in a target-specific manner and is related to functional properties of the stimulated node within the brain network.Item Gamma Oscillations During Episodic Memory Processing Provide Evidence for Functional Specialization in the Longitudinal Axis of the Human Hippocampus(Wiley, 2018-11-05) Lin, Jui-Jui; Umbach, Gray; Rugg, Michael D.; Lega, Bradley; Rugg, Michael D.The question of whether the anterior and posterior hippocampus serve different or complementary functional roles during episodic memory processing has been motivated by noteworthy findings in rodent experiments and from noninvasive studies in humans. Researchers have synthesized these data to postulate several models of functional specialization, However, the issue has not been explored in detail using direct brain recordings. We recently published evidence that theta power increases during episodic memory encoding occur in the posterior hippocampus in humans. In our current investigation we analyzed an expanded data set of 32 epilepsy patients undergoing stereo EEG seizure mapping surgery with electrodes precisely targeted to the anterior and posterior hippocampus simultaneously who performed an episodic memory task. Using a repeated measures design, we looked for an interaction between encoding versus retrieval differences in gamma oscillatory power and anterior versus posterior hippocampal location. Our findings are consistent with a recently articulated model (the HERNET model) favoring posterior hippocampal activation during retrieval related processing. We also tested for encoding versus retrieval differences in the preferred gamma frequency band (high versus low gamma oscillations) motivated by published rodent data.Item Modulation of Oscillatory Power and Connectivity in the Human Posterior Cingulate Cortex Supports the Encoding and Retrieval of Episodic Memories(MIT Press) Lega, Bradley; Germi, James; Rugg, Michael D.; Rugg, Michael D.Existing data from noninvasive studies have led researchers to posit that the posterior cingulate cortex (PCC) supports mnemonic processes: It exhibits degeneration in memory disorders, and fMRI investigations have demonstrated memory-related activation principally during the retrieval of memory items. Despite these data, the role of the PCC in episodic memory has received only limited treatment using the spatial and temporal precision of intracranial EEG, with previous analyses focused on item retrieval. Using data gathered from 21 human participants who underwent stereo-EEG for seizure localization, we characterized oscillatory patterns in the PCC during the encoding and retrieval of episodic memories. We identified a subsequent memory effect during item encoding characterized by increased gamma band oscillatory power and a low-frequency power desynchronization. Fourteen participants had stereotactic electrodes located simultaneously in the hippocampus and PCC, and with these unique data, we describe connectivity changes between these structures that predict successful item encoding and that precede item retrieval. Oscillatory power during retrieval matched the pattern we observed during encoding, with low-frequency (below 15 Hz) desynchronization and a gamma band (especially high gamma, 70-180 Hz) power increase. Encoding is characterized by synchrony between the hippocampus and PCC, centered at 3 Hz, consistent with other observations of properties of this oscillation akin to those for rodent theta activity. We discuss our findings in light of existing theories of episodic memory processing, including the information via desynchronization hypothesis and retrieved context theory, and examine how our data fit with existing theories for the functional role of the PCC. These include a postulated role for the PCC in modulating internally directed attention and for representing or integrating contextual information for memory items.Item Relationships Between Age, Subjective and Objective Measures of Recollection, and Pre-stimulus Neural Correlates of Memory Encoding and Retrieval(December 2023) Alghamdi, Saad Ali; Rugg, Michael D.; Rennaker II, Robert L.; Filbey, Francesca; Rodrigue, Karen; Krawczyk, DanielIt is well established that episodic memory (i.e., memory for personal unique events) declines with age. There is some evidence, however, that the decline might be moderated by the estimation methods. That is, while the impact of age on recollection is consistently evident when using ‘objective’ memory procedures (e.g., a source memory task), recollection estimated from ‘subjective’ procedures such as the Remember/Know procedure gives rise to inconsistent impact of age on recollection. Therefore, it was suggested that the null impact of age on recollection reported in some prior studies might be due to a differential impact of age on subjective versus objective aspects of recollection. In the first study covered in Chapter 2, we examined this hypothesis by directly contrasting recollection estimated from the source memory procedure with recollection estimated from the R/K procedure in the same sample of young and older adults. Our results revealed an equivalent impact of age on recollection estimated from both procedures. Hence, we found no evidence that the impact of age was moderated by the subjective and objective aspects of recollection. In Chapter 3, we conducted an ERP study to examine the relationship between retrieval mode (i.e., pre-retrieval processing suggested to facilitate episodic retrieval) and recollection on a trial-by-trial basis and whether this relationship is moderated by the impact of age. Our results revealed that the pre-retrieval ERP effects associated with recollection was distinct from those associated with non-semantic judgements. The pre-retrieval ERP effects took the shape of more negative going ERPs preceding recollected items compared to that preceding non-episodic semantic items. The results are in line with the suggestion that retrieval mode facilitates episodic retrieval. Of importance, we found no evidence that this pattern of effects was moderated by age. Chapter 4 covers the impact of age on a different aspect of episodic memory. Here, we examined the impact of age on pre-stimulus subsequent memory effects (pre-stimulus SMEs). Only a few studies examined age-related differences in prestimulus SMEs and reported mixed findings. Our results revealed an impact of age on prestimulus SMEs. That is, the pattern of results demonstrated more negative-going ERPs for correct than incorrect source judgements in the young age group only. An important question is whether the pre-stimulus SMEs predict behavioral age-related differences in recollection. Indeed, the impact of age on the pre-stimulus SMEs corresponded to the impact of age on recollection and recognition memory in our behavioral findings. Taken as a whole, the present dissertation provides the field of cognitive aging and memory with valuable insights in understanding the impact of age on recollection from different methodological and memory stages’ perspectives.Item Structural Heterogeneity in Neuronal Aging: Insights From Micro and Macro Structural Neuroimaging(2022-12-01T06:00:00.000Z) Hoagey, David Anthony; Kennedy, Kristen M; Goffman, Lisa A; Rodrigue, Karen; Rugg, Michael D.; Seaman, Kendra LNeuroimaging research is making unprecedented gains towards a better understanding of what constitutes healthy brain structure and function in aging. Decades, if not centuries, of ex vivo histological work have demonstrated the complexity of cytoarchitectural and myeloarchitectural underpinnings of neuronal organization that we are only beginning to investigate in the living brain. With advancing techniques, we can now investigate in vivo estimates quantifying biological proxies of structural brain health. The current studies aimed to capitalize on both our histological understanding of the architectural features defining brain structure, and modern neuroimaging estimates of structural health, to expand upon our understanding of the processes involved in nominal brain aging. In a healthy lifespan sample of adults, we acquired multiple neuroimaging sequences designed to characterize the health of gray and white matter tissue compartments. By mapping these estimates to a cytoarchitecturally defined brain atlas we were able to 1) examine the regional differentiation of the coupling of gray matter morphometry and health proxies from the neighboring white matter most likely to innervate these regions and 2) investigate the age-related associations between estimates of neurite health and organization within the gray matter of specific cortical types. We found that there were regionally distinct patterns of association that generally pointed to an age-related vulnerability of structure in higher-order cognitive centers. These regions demonstrated greater coupling in morphometry with neighboring white matter health proxies, as well as elevated organizational heterogeneity within these cortical types. Our results demonstrate that aging trajectories in brain structure follow specific patterns that map on to several key theories posited in prior research such as retrogenesis, phylogenetic, or ontogenetic precedence. However, these findings provide novel evidence emphasizing the importance of myelin content and plasticity as well as the role of glia, specifically oligodendrocyte function, and the high cost of brain maintenance, prompting further investigation of additional conceptualizations of structural brain aging.Item The Neural Correlates of Recollection and Post-Retrieval Monitoring in Younger and Older Adults(2019-08) Horne, Erin D.; Rugg, Michael D.Episodic retrieval is not a homogeneous process, but rather involves the engagement of several dissociable cognitive processes. These processes include those specialized for memory functions, such as hippocampally mediated pattern completion processes, as well as generic cognitive control processes linked with activity in the frontal cortex. Thus, age-related decline in episodic memory performance is not consistent across all aspects of retrieval, but dissociable subprocesses contributing to successful retrieval are affected to differing extents. To examine agerelated differences in processes contributing to retrieval, we investigated the neural correlates of recollection and post-retrieval monitoring in samples of younger and older adults using ERP (experiment 1: Ns 20 per group) and fMRI (experiment 2: Ns 28 per group). In experiment 1, we focused on modulation of recollection-related activity (operationalized as subjective report using the RKN procedure) as a function of source accuracy. In experiment 2, we examined how varying the global task demand of an associative recognition task by adding a secondary tone detection task might modulate prefrontal monitoring effects in younger and older adults. Across experiments, we found that both age groups activated a common set of regions supporting memory retrieval (in most cases), but that older adults demonstrated less modulation of recollection- and monitoring-related activity. This finding suggests that a breakdown in the ability to dynamically modulate activity supporting retrieval according to online task demands may be a key factor underlying the decline in memory performance with advancing age.Item The Relationship Between Age, Cognitive Performance, and the Neural Correlates of Episodic Memory Encoding and Retrieval(2022-12-01T06:00:00.000Z) Srokova, Sabina 1995-; Wig, Gagan; Rugg, Michael D.; Seaman, Kendra; Kennedy, Kristen; O'Toole, Alice J.Cognitive aging is associated with a disproportionate decline in episodic memory, the ability to recollect contextual details of previously experienced events. Understanding the mechanisms which underlie age-related episodic memory decline is a critical precursor to developing interventions aimed at ameliorating memory deficits in healthy and pathological aging. Considerable empirical evidence suggests that age-related episodic memory deficits arise from numerous factors which differentially impact multiple neural processes and brain regions. The present work focuses on examining some contributors which have been proposed under this framework. Study 1 investigates age-related neural dedifferentiation, a phenomenon characterized by age-related reductions in the neural selectivity of category-selective cortical regions. Our analyses reveal robust age effects on neural differentiation for scene, but not for face stimuli, adding to prior evidence indicating that age-related neural dedifferentiation is not a ubiquitous phenomenon. Study 1 also reveals that the strength of neural differentiation during encoding is predictive of subsequent memory performance independently of age. The work in Study 1 is complemented by Study 4 in which neural dedifferentiation is operationalized at the level of individual exemplars (as opposed to stimulus categories). To examine item-level neural differentiation, we framed our analyses in terms of age differences in repetition suppression effects, which revealed null effects of age. Collectively, Studies 1 and 4 highlighting the functional significance of age-related neural dedifferentiation and emphasize the urgent need to advance our understanding of the factors that lead to age differences in neural selectivity and specificity. Moving on to Study 2, the work described therein examines age differences in retrieval gating, the ability to regulate the retrieval of mnemonic information according to behavioral goals. Study 2 provides the first evidence that older adults do not engage in retrieval gating, indicating that episodic memory decline may arise as consequence of a decline in the engagement of goal- dependent retrieval strategies. Lastly, Study 3 reveals novel evidence for age differences in the retrieval-related anterior shift, the phenomenon whereby the peak neural activity at retrieval occurs in more anterior portions of single cortical regions relative to encoding. Our analyses show that the shift is greater in older than younger adults, and that greater shift is associated with worse memory performance independently of age. In line with prior empirical work proposing a posterior (perceptual) to anterior (conceptual) gradient in the brain, these findings indicate that the age- related increase in anterior shift may be reflective of an increased reliance on gist-based low- fidelity retrieval in older age. Taken together, the studies comprising this dissertation enhance our understanding of the behavioral and neural correlates of cognitive aging and advance the collective knowledge in the field cognitive neuroscience of age-related episodic memory decline.Item The Relationship Between Age, Neural Differentiation, and Memory Performance(Society for Neuroscience, 2018-11-02) Koen, Joshua D.; Hauck, Nedra; Rugg, Michael D.; 0000-0002-7286-5084 (Koen, JD); 0000-0002-0397-5749 (Rugg, MD); Koen, Joshua D.; Hauck, Nedra; Rugg, Michael D.Healthy aging is associated with decreased neural selectivity (dedifferentiation) in category-selective cortical regions. This finding has prompted the suggestion that dedifferentiation contributes to age-related cognitive decline. Consistent with this possibility, dedifferentiation has been reported to negatively correlate with fluid intelligence in older adults. Here, we examined whether dedifferentiation is associated with performance in another cognitive domain- episodic memory-that is also highly vulnerable to aging. Given the proposed role of dedifferentiation in age-related cognitive decline, we predicted there would be a stronger link between dedifferentiation and episodic memory performance in older than in younger adults. Young (18 -30 years) and older (64 -75 years) male and female humans underwent fMRI scanning while viewing images of objects and scenes before a subsequent recognition memory test. We computed a differentiation index in two regions of interest (ROIs): parahippocampal place area (PPA) and lateral occipital complex (LOC). This index quantified the selectivity of the BOLD response to preferred versus nonpreferred category of an ROI (scenes for PPA, objects for LOC). The differentiation index in the PPA, but not the LOC, was lower in older than in younger adults. Additionally, the PPA differentiation index predicted recognition memory performance for the studied items. This relationship was independent of and not moderated by age. The PPA differentiation index also predicted performance on a latent "fluency" factor derived from a neuropsychological test battery; this relationship was also age invariant. These findings suggest that two independent factors, one associated with age, and the other with cognitive performance, influence neural differentiation.Item Time-varying Sources and Vascular Contributions to Age-accompanied Functional Brain Network Re-organization(2022-12-01T06:00:00.000Z) Han, Liang; Wig, Gagan; Stillman, Robert D; Rugg, Michael D.; Rypma, Bart; Gel, YuliaThe brain is a complex network of interacting brain areas that can be further divided into segregated functional systems. Resting-state system segregation is a feature of brain network organization that has relevance to brain function in both health and disease across adult lifespan. It is unclear what gives rise to system segregation and the individual differences in this brain network measure. In this dissertation, two aspects of this important question are investigated: (1) Do vascular factors contribute to relationships between age and system segregation across the adult lifespan? and (2) Can sources of time-varying information help account for relationships between aging and system segregation? The interplay between these questions reveals how the temporal evolution of system re-configuration at a short time scale impacts more stable individual features of large-scale network organization, in the context of differences in vascular health of adult individuals. This dissertation was accomplished by incorporating data from a total of 894 unique participants, over 3 independent studies (age range: 20 – 100 years) and including multiple neuroimaging modalities and measures of participant health and demographics. The contribution of vascular factors towards relationships between age and resting-state system segregation is first investigated. There exist relationships between age and vascular measures, including cardiovascular health (CVH) and cerebrovascular reactivity (CVR). Age-related decreases of system segregation persist after controlling for vascular-related variance. This is demonstrated by (i) computing system segregation regional CVR-corrected signals within each participant, and (ii) including CVH as a participant-level covariate in the models. These results demonstrate that age-related differences in system segregation cannot be fully attributed to differences in cerebrovascular and cardiovascular factors. To examine the contribution of time-varying information to system segregation, I examine the relationship between resting-state BOLD signal variability and system segregation. After controlling for vascular confounds by (i) estimating BOLD variability using CVR-corrected signals, (ii) including CVH as a covariate in the model, there is an absence of a relationship between age and BOLD variability, revealing that vascular factors serve as a major source of variance explaining previously reported relationships between age and resting-state BOLD signal variability. Further, with correction of vascular factors, BOLD variability does not relate to system segregation. An additional source of time-varying information is evaluated in relation to system segregation, focused on co-fluctuation amplitude of the resting-state time-series. Moments of greater co- fluctuation pattern across edges are identified (events), during which functional brain networks are highly modular relative to non-event moments. I demonstrate that the number of events that are present in an individual’s resting-state time-series is related to their system segregation. However, I next demonstrate that age-accompanied decreases of system segregation are evident across all the moments, irrespective of co-fluctuation amplitude of edges. Collectively, these findings reveal that while high co-fluctuation moments (events) may contribute towards establishing an individual’s system segregation, brain network re-organization exists across all time points of a resting-state scan. In sum, this dissertation provides important support that resting-state system segregation measures brain network re-organization across the adult lifespan. This measure is independent from vascular differences within individuals, and provides critical evidence of brain aging that is consistently evident across periods of rest. Serving as a biomarker of functional brain network integrity, system segregation further supports the application of this approach towards measuring individual brain health across the lifespan.Item Transcranial Magnetic Stimulation of the Left Angular Gyrus During Encoding Does not Impair Associative Memory Performance(Routledge) Koen, Joshua D.; Thakral, P. P.; Rugg, Michael D.; Koen, Joshua D.; Rugg, Michael D.The left angular gyrus (AG) is thought to play a critical role in episodic retrieval and has been implicated in the recollection of specific details of prior episodes. Motivated by recent fMRI studies in which it was reported that elevated neural activity in left AG during study is predictive of subsequent associative memory, the present study investigated whether the region plays a causal role in associative memory encoding. Participants underwent online transcranial magnetic stimulation (TMS) while encoding word pairs prior to an associative memory test. We predicted that TMS to left AG during encoding would result in reduced subsequent memory accuracy, especially for estimates of recollection. The results did not support this prediction: estimates of both recollection and familiarity-driven recognition were essentially identical for words pairs encoded during TMS to left AG relative to a vertex control site. These results suggest that the left AG may not play a necessary role in associative memory encoding. TMS to left AG did however affect confidence for incorrect ‘intact’ judgments to rearranged pairs and incorrect ‘rearranged’ judgments to intact pairs. These findings suggest that the left AG supports encoding processes that contribute to aspects of subjective mnemonic experience. © 2018 Informa UK Limited, trading as Taylor & Francis Group