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Callow DD, Kommula Y, Stark CEL, Smith JC. Acute cycling exercise and hippocampal subfield function and microstructure in healthy older adults. Hippocampus 2023; 33:1123-1138. [PMID: 37526119 PMCID: PMC10543457 DOI: 10.1002/hipo.23571] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2023] [Revised: 07/04/2023] [Accepted: 07/10/2023] [Indexed: 08/02/2023]
Abstract
Aging is associated with deterioration in dentate gyrus (DG) and CA3, both crucial hippocampal subfields for age susceptible memory processes such as mnemonic discrimination (MD). Meanwhile, a single aerobic exercise session alters DG/CA3 function and neural activity in both rats and younger adults and can elicit short-term microstructural alterations in the hippocampus of older adults. However, our understanding of the effects of acute exercise on hippocampal subfield integrity via function and microstructure in older adults is limited. Thus, a within subject-design was employed to determine if 20-min of moderate to vigorous aerobic exercise alters bilateral hippocampal subfield function and microstructure using high-resolution functional magnetic resonance imaging (fMRI) during an MD task (n = 35) and high angular resolution multi-shell diffusion imaging (n = 31), in healthy older adults, compared to seated rest. Following the exercise condition, participants exhibited poorer MD performance, particularly when their perception of effort was higher. Exercise was also related to lower MD-related activity within the DG/CA3 but not CA1 subfield. Finally, after controlling for whole brain gray matter diffusion, exercise was associated with lower neurite density index (NDI) within the DG/CA3. However, exercise-related differences in DG/CA3 activity and NDI were not associated with differences in MD performance. Our results suggest moderate to vigorous aerobic exercise may temporarily inhibit MD performance, and suppress DG/CA3 MD-related activity and NDI, potentially through neuroinflammatory/glial processes. However, additional studies are needed to confirm whether these short-term changes in behavior and hippocampal subfield neurophysiology are beneficial and how they might relate to long-term exercise habits.
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Affiliation(s)
- Daniel D. Callow
- Department of Kinesiology, University of Maryland, College Park, MD, USA
- Program in Neuroscience and Cognitive Science, University of Maryland, College Park, MD, USA
| | - Yash Kommula
- Department of Kinesiology, University of Maryland, College Park, MD, USA
- Program in Neuroscience and Cognitive Science, University of Maryland, College Park, MD, USA
| | - Craig E. L. Stark
- Department of Neurobiology and Behavior, University of California, Irvine, CA, USA
| | - J. Carson Smith
- Department of Kinesiology, University of Maryland, College Park, MD, USA
- Program in Neuroscience and Cognitive Science, University of Maryland, College Park, MD, USA
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Amer T, Davachi L. Extra-hippocampal contributions to pattern separation. eLife 2023; 12:82250. [PMID: 36972123 PMCID: PMC10042541 DOI: 10.7554/elife.82250] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2022] [Accepted: 03/21/2023] [Indexed: 03/29/2023] Open
Abstract
Pattern separation, or the process by which highly similar stimuli or experiences in memory are represented by non-overlapping neural ensembles, has typically been ascribed to processes supported by the hippocampus. Converging evidence from a wide range of studies, however, suggests that pattern separation is a multistage process supported by a network of brain regions. Based on this evidence, considered together with related findings from the interference resolution literature, we propose the 'cortico-hippocampal pattern separation' (CHiPS) framework, which asserts that brain regions involved in cognitive control play a significant role in pattern separation. Particularly, these regions may contribute to pattern separation by (1) resolving interference in sensory regions that project to the hippocampus, thus regulating its cortical input, or (2) directly modulating hippocampal processes in accordance with task demands. Considering recent interest in how hippocampal operations are modulated by goal states likely represented and regulated by extra-hippocampal regions, we argue that pattern separation is similarly supported by neocortical-hippocampal interactions.
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Affiliation(s)
- Tarek Amer
- Department of Psychology, University of Victoria, Victoria, Canada
| | - Lila Davachi
- Department of Psychology, Columbia University, New York, United States
- Nathan Kline Research Institute, Orangeburg, United States
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Age-related differences in encoding-retrieval similarity and their relationship to false memory. Neurobiol Aging 2022; 113:15-27. [DOI: 10.1016/j.neurobiolaging.2022.01.011] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2021] [Revised: 01/28/2022] [Accepted: 01/31/2022] [Indexed: 12/26/2022]
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Lin Z, Hou G, Yao Y, Zhou Z, Zhu F, Liu L, Zeng L, Yang Y, Ma J. 40-Hz Blue Light Changes Hippocampal Activation and Functional Connectivity Underlying Recognition Memory. Front Hum Neurosci 2022; 15:739333. [PMID: 34975431 PMCID: PMC8716555 DOI: 10.3389/fnhum.2021.739333] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2021] [Accepted: 11/19/2021] [Indexed: 12/04/2022] Open
Abstract
Research on light modulation has typically examined the wavelength, intensity, and exposure time of light, and measured rhythm, sleep, and cognitive ability to evaluate the regulatory effects of light variables on physiological and cognitive functions. Although the frequency of light is one of the main dimensions of light, few studies have attempted to manipulate it to test the effect on brain activation and performance. Recently, 40-Hz light stimulation has been proven to significantly alleviate deficits in gamma oscillation of the hippocampus caused by Alzheimer’s disease. Although this oscillation is one of the key functional characteristics of performing memory tasks in healthy people, there is no evidence that 40-Hz blue light exposure can effectively regulate brain activities related to complex cognitive tasks. In the current study, we examined the difference in the effects of 40-Hz light or 0-Hz light exposure on brain activation and functional connectivity during a recognition memory task. Through joint augmentation of visual area activation, 40-Hz light enhanced brain areas mostly in the limbic system that are related to memory, such as the hippocampus and thalamus. Conversely, 0-Hz light enhanced brain areas mostly in the prefrontal cortex. Additionally, functional connection analysis, with the hippocampus as the seed point, showed that 40-Hz light enhanced connection with the superior parietal lobe and reduced the connection with the default network. These results indicate that light at a frequency of 40 Hz can change the activity and functional connection of memory-related core brain areas. They also indicate that in the use of light to regulate cognitive functions, its frequency characteristics merit attention.
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Affiliation(s)
- Zhenglong Lin
- College of Electronics and Information Engineering, Shenzhen University, Shenzhen, China
| | - Gangqiang Hou
- Department of Radiology, Shenzhen Kangning Hospital, Shenzhen Mental Health Center, Shenzhen, China
| | - Youli Yao
- Department of Physiology, School of Basic Medical Sciences, Shenzhen University Health Sciences Center, Shenzhen University, Shenzhen, China
| | - Zhifeng Zhou
- Department of Radiology, Shenzhen Kangning Hospital, Shenzhen Mental Health Center, Shenzhen, China
| | - Feiqi Zhu
- Cognitive Impairment Ward of Neurology Department, The Third Affiliated Hospital of Shenzhen University Medical College, Shenzhen, China
| | - Linjing Liu
- College of Electronics and Information Engineering, Shenzhen University, Shenzhen, China
| | - Lingwu Zeng
- College of Electronics and Information Engineering, Shenzhen University, Shenzhen, China
| | - Yatao Yang
- College of Electronics and Information Engineering, Shenzhen University, Shenzhen, China
| | - Junxian Ma
- College of Electronics and Information Engineering, Shenzhen University, Shenzhen, China
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Wahlheim CN, Christensen AP, Reagh ZM, Cassidy BS. Intrinsic functional connectivity in the default mode network predicts mnemonic discrimination: A connectome-based modeling approach. Hippocampus 2021; 32:21-37. [PMID: 34821439 DOI: 10.1002/hipo.23393] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Revised: 11/09/2021] [Accepted: 11/10/2021] [Indexed: 12/31/2022]
Abstract
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 temporal-prefrontal 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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Affiliation(s)
- Christopher N Wahlheim
- Department of Psychology, University of North Carolina at Greensboro, Greensboro, North Carolina, USA
| | | | - Zachariah M Reagh
- Department of Psychological & Brain Sciences, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Brittany S Cassidy
- Department of Psychology, University of North Carolina at Greensboro, Greensboro, North Carolina, USA
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Johnson SA, Zequeira S, Turner SM, Maurer AP, Bizon JL, Burke SN. Rodent mnemonic similarity task performance requires the prefrontal cortex. Hippocampus 2021; 31:701-716. [PMID: 33606338 PMCID: PMC9343235 DOI: 10.1002/hipo.23316] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2020] [Revised: 01/01/2021] [Accepted: 01/23/2021] [Indexed: 11/07/2023]
Abstract
Mnemonic similarity task performance, in which a known target stimulus must be distinguished from similar lures, is supported by the hippocampus and perirhinal cortex. Impairments on this task are known to manifest with advancing age. Interestingly, disrupting hippocampal activity leads to mnemonic discrimination impairments when lures are novel, but not when they are familiar. This observation suggests that other brain structures support discrimination abilities as stimuli are learned. The prefrontal cortex (PFC) is critical for retrieval of remote events and executive functions, such as working memory, and is also particularly vulnerable to dysfunction in aging. Importantly, the medial PFC is reciprocally connected to the perirhinal cortex and neuron firing in this region coordinates communication between lateral entorhinal and perirhinal cortices to presumably modulate hippocampal activity. This anatomical organization and function of the medial PFC suggests that it contributes to mnemonic discrimination; however, this notion has not been empirically tested. In the current study, rats were trained on a LEGO object-based mnemonic similarity task adapted for rodents, and surgically implanted with guide cannulae targeting prelimbic and infralimbic regions of the medial PFC. Prior to mnemonic discrimination tests, rats received PFC infusions of the GABAA agonist muscimol. Analyses of expression of the neuronal activity-dependent immediate-early gene Arc in medial PFC and adjacent cortical regions confirmed muscimol infusions led to neuronal inactivation in the infralimbic and prelimbic cortices. Moreover, muscimol infusions in PFC impaired mnemonic discrimination performance relative to the vehicle control across all testing blocks when lures shared 50-90% feature overlap with the target. Thus, in contrast hippocampal infusions, PFC inactivation impaired target-lure discrimination regardless of the novelty or familiarity of the lures. These findings indicate the PFC plays a critical role in mnemonic similarity task performance, but the time course of PFC involvement is dissociable from that of the hippocampus.
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Affiliation(s)
- Sarah A. Johnson
- Evelyn F. and William L. McKnight Brain Institute, Gainesville, Florida
- Department of Neuroscience, University of Florida, Gainesville, Florida
| | - Sabrina Zequeira
- Evelyn F. and William L. McKnight Brain Institute, Gainesville, Florida
- Department of Neuroscience, University of Florida, Gainesville, Florida
| | - Sean M. Turner
- Department of Clinical Health Psychology, University of Florida, Gainesville, Florida
| | - Andrew P. Maurer
- Evelyn F. and William L. McKnight Brain Institute, Gainesville, Florida
- Department of Neuroscience, University of Florida, Gainesville, Florida
- Department of Biomedical Engineering, University of Florida, Gainesville, Florida
| | - Jennifer L. Bizon
- Evelyn F. and William L. McKnight Brain Institute, Gainesville, Florida
- Department of Neuroscience, University of Florida, Gainesville, Florida
| | - Sara N. Burke
- Evelyn F. and William L. McKnight Brain Institute, Gainesville, Florida
- Department of Neuroscience, University of Florida, Gainesville, Florida
- Institute on Aging, University of Florida, Gainesville, Florida
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Nash MI, Hodges CB, Muncy NM, Kirwan CB. Pattern separation beyond the hippocampus: A high-resolution whole-brain investigation of mnemonic discrimination in healthy adults. Hippocampus 2021; 31:408-421. [PMID: 33432734 DOI: 10.1002/hipo.23299] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2019] [Revised: 12/07/2020] [Accepted: 01/02/2021] [Indexed: 12/28/2022]
Abstract
Episodic memory depends on the computational process of pattern separation in order to establish distinct memory representations of similar episodes. Studies of pattern separation in humans rely on mnemonic discrimination tasks, which have been shown to tax hippocampal-dependent pattern separation. Although previous neuroimaging research has focused on hippocampal processing, little is known about how other brain regions, known to be involved in recognition memory performance, are involved in mnemonic discrimination tasks. Conversely, neuroimaging studies of pattern separation with whole-brain coverage lack spatial resolution to localize activation to hippocampal subfields. In this study, 48 healthy young adult participants underwent whole-brain high-resolution functional MRI (fMRI) scanning while completing a mnemonic discrimination task. A priori region-of-interest analyses revealed activation patterns consistent with pattern separation in distinct hippocampal subregions, particularly in the subiculum. Connectivity analyses revealed a network of cortical regions consistent with the memory retrieval network where fMRI activation was correlated with hippocampal activation. An exploratory whole-brain analysis revealed widespread activation differentially associated with performance of the mnemonic discrimination task. Taken together, these results suggest that a network of brain regions contribute to mnemonic discrimination performance, with the hippocampus and parahippocampal cortex as a hub in the network displaying clear signals consistent with pattern separation and regions such as the dorsal medial prefrontal cortex particularly important for successful lure discrimination.
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Affiliation(s)
- Michelle I Nash
- Department of Behavioral Sciences and Leadership, United States Air Force Academy, USAF Academy, Colorado, USA
| | - Cooper B Hodges
- Department of Psychology, Brigham Young University, Provo, Utah, USA.,Department of Neurology, School of Medicine, University of Utah, Salt Lake City, Utah, USA
| | - Nathan M Muncy
- Department of Psychology, Brigham Young University, Provo, Utah, USA
| | - C Brock Kirwan
- Department of Psychology, Brigham Young University, Provo, Utah, USA.,Neuroscience Center, Brigham Young University, Provo, Utah, USA
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Klippenstein JL, Stark SM, Stark CEL, Bennett IJ. Neural substrates of mnemonic discrimination: A whole-brain fMRI investigation. Brain Behav 2020; 10:e01560. [PMID: 32017430 PMCID: PMC7066353 DOI: 10.1002/brb3.1560] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/16/2019] [Revised: 12/20/2019] [Accepted: 01/11/2020] [Indexed: 12/23/2022] Open
Abstract
INTRODUCTION A fundamental component of episodic memory is the ability to differentiate new and highly similar events from previously encountered events. Numerous functional magnetic resonance imaging (fMRI) studies have identified hippocampal involvement in this type of mnemonic discrimination (MD), but few studies have assessed MD-related activity in regions beyond the hippocampus. Therefore, the current fMRI study examined whole-brain activity in healthy young adults during successful discrimination of the test phase of the Mnemonic Similarity Task. METHOD In the study phase, participants made "indoor"/"outdoor" judgments to a series of objects. In the test phase, they made "old"/"new" judgments to a series of probe objects that were either repetitions from the memory set (targets), similar to objects in the memory set (lures), or novel. We assessed hippocampal and whole-brain activity consistent with MD using a step function to identify where activity to targets differed from activity to lures with varying degrees of similarity to targets (high, low), responding to them as if they were novel. RESULTS Results revealed that the hippocampus and occipital cortex exhibited differential activity to repeated stimuli relative to even highly similar stimuli, but only hippocampal activity predicted discrimination performance. CONCLUSIONS These findings are consistent with the notion that successful MD is supported by the hippocampus, with auxiliary processes supported by cortex (e.g., perceptual discrimination).
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Affiliation(s)
| | - Shauna M. Stark
- Department of Neurobiology & BehaviorUniversity of CaliforniaIrvineCalifornia
| | - Craig E. L. Stark
- Department of Neurobiology & BehaviorUniversity of CaliforniaIrvineCalifornia
| | - Ilana J. Bennett
- Department of PsychologyUniversity of CaliforniaRiversideCalifornia
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