Rugg, Michael D.
Permanent URI for this collectionhttps://hdl.handle.net/10735.1/3934
Michael Rugg is Professor and holds the Distinguished Chair in Behavioral and Brain Sciences. He also serves as the Co-Director of the Center for Vital Longevity and is the head of the fNIM (Functional Neuro-Imaging of Memory) Laboratory. His research interests include the cognitive and neural bases of memory encoding and retrieval, as well as how and why memory function differs as a result of healthy aging or neurological disease. Learn more about Dr. Rugg on his Center for Vital Longevity Faculty, BBS People, Endowed Professorships and Chairs pages and the fNIM Laboratory website.
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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 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 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 GroupItem 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 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 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.;