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Jeffery KJ. The mosaic structure of the mammalian cognitive map. Learn Behav 2024; 52:19-34. [PMID: 38231426 PMCID: PMC10923978 DOI: 10.3758/s13420-023-00618-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/27/2023] [Indexed: 01/18/2024]
Abstract
The cognitive map, proposed by Tolman in the 1940s, is a hypothetical internal representation of space constructed by the brain to enable an animal to undertake flexible spatial behaviors such as navigation. The subsequent discovery of place cells in the hippocampus of rats suggested that such a map-like representation does exist, and also provided a tool with which to explore its properties. Single-neuron studies in rodents conducted in small singular spaces have suggested that the map is founded on a metric framework, preserving distances and directions in an abstract representational format. An open question is whether this metric structure pertains over extended, often complexly structured real-world space. The data reviewed here suggest that this is not the case. The emerging picture is that instead of being a single, unified construct, the map is a mosaic of fragments that are heterogeneous, variably metric, multiply scaled, and sometimes laid on top of each other. Important organizing factors within and between fragments include boundaries, context, compass direction, and gravity. The map functions not to provide a comprehensive and precise rendering of the environment but rather to support adaptive behavior, tailored to the species and situation.
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Affiliation(s)
- Kate J Jeffery
- School of Psychology and Neuroscience, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK.
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2
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Crown LM, Gray DT, Schimanski LA, Barnes CA, Cowen SL. Aged Rats Exhibit Altered Behavior-Induced Oscillatory Activity, Place Cell Firing Rates, and Spatial Information Content in the CA1 Region of the Hippocampus. J Neurosci 2022; 42:4505-4516. [PMID: 35477900 PMCID: PMC9172068 DOI: 10.1523/jneurosci.1855-21.2022] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2021] [Revised: 03/18/2022] [Accepted: 04/14/2022] [Indexed: 11/21/2022] Open
Abstract
Hippocampal gamma and theta oscillations are associated with mnemonic and navigational processes and adapt to changes in the behavioral state of an animal to optimize spatial information processing. It has been shown that locomotor activity modulates gamma and theta frequencies in rats, although how age alters this modulation has not been well studied. Here, we examine gamma and theta local-field potential and place cell activity in the hippocampus CA1 region of young and old male rats as they performed a spatial eye-blink conditioning task across 31 d. Although mean gamma frequency was similar in both groups, gamma frequency increased with running speed at a slower rate in old animals. By contrast, theta frequencies scaled with speed similarly in both groups but were lower across speeds in old animals. Although these frequencies scaled equally well with deceleration and speed, acceleration was less correlated with gamma frequency in both age groups. Additionally, spike phase-locking to gamma, but not theta, was greater in older animals. Finally, aged rats had reduced within-field firing rates but greater spatial information per spike within the field. These data support a strong relationship between locomotor behavior and local-field potential activity and suggest that age significantly affects this relationship. Furthermore, observed changes in CA1 place cell firing rates and information content lend support to the hypothesis that age may result in more general and context-invariant hippocampal representations over more detailed information. These results may explain the observation that older adults tend to recall the gist of an experience rather than the details.SIGNIFICANCE STATEMENT Hippocampal oscillations and place cell activity are sensitive to sensorimotor input generated from active locomotion, yet studies of aged hippocampal function often do not account for this. By considering locomotion and spatial location, we identify novel age-associated differences in the scaling of oscillatory activity with speed, spike-field coherence, spatial information content, and within-field firing rates of CA1 place cells. These results indicate that age has an impact on the relationship between locomotion and hippocampal oscillatory activity, perhaps indicative of alterations to afferent input. These data also support the hypothesis that aged hippocampal place cells, compared with young, may more often represent more general spatial information. If true, these results may help explain why older humans tend to recall less specific and more gist-like information.
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Affiliation(s)
- Lindsey M Crown
- Evelyn F. McKnight Brain Institute, University of Arizona, Tucson, Arizona 85724
- Department of Psychology, University of Arizona, Tucson, Arizona 85721
| | - Daniel T Gray
- Evelyn F. McKnight Brain Institute, University of Arizona, Tucson, Arizona 85724
- Departments of Neurology and Neuroscience, University of Arizona, Tucson, Arizona 85724
| | - Lesley A Schimanski
- Evelyn F. McKnight Brain Institute, University of Arizona, Tucson, Arizona 85724
| | - Carol A Barnes
- Evelyn F. McKnight Brain Institute, University of Arizona, Tucson, Arizona 85724
- Department of Psychology, University of Arizona, Tucson, Arizona 85721
- Departments of Neurology and Neuroscience, University of Arizona, Tucson, Arizona 85724
| | - Stephen L Cowen
- Evelyn F. McKnight Brain Institute, University of Arizona, Tucson, Arizona 85724
- Department of Psychology, University of Arizona, Tucson, Arizona 85721
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3
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Impaired remapping of social relationships in older adults. Sci Rep 2021; 11:21910. [PMID: 34753971 PMCID: PMC8578667 DOI: 10.1038/s41598-021-01258-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2021] [Accepted: 10/19/2021] [Indexed: 11/08/2022] Open
Abstract
Social relationships are a central aspect of our everyday life, yet our ability to change established social relationships is an under-investigated topic. Here, we use the concept of cognitive mapping to investigate the plasticity of social relationships in younger and older adults. We describe social relationships within a 'social space', defined as a two-dimensional grid composed of the axis 'power' and 'affiliation', and investigate it using a 3D virtual environment with interacting avatars. We show that participants remap dimensions in 'social space' when avatars show conflicting behavior compared to consistent behavior and that, while older adults show similar updating behavior than younger adults, they show a distinct reduction in remapping social space. Our data provide first evidence that older adults show more rigid social behavior when avatars change their behavior in the dimensions of power and affiliation, which may explain age-related social behavior differences in everyday life.
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Abstract
SIGNIFICANCE Oxidative stress increases in the brain with aging and neurodegenerative diseases. Previous work emphasized irreversible oxidative damage in relation to cognitive impairment. This research has evolved to consider a continuum of alterations, from redox signaling to oxidative damage, which provides a basis for understanding the onset and progression of cognitive impairment. This review provides an update on research linking redox signaling to altered function of neural circuits involved in information processing and memory. Recent Advances: Starting in middle age, redox signaling triggers changes in nervous system physiology described as senescent physiology. Hippocampal senescent physiology involves decreased cell excitability, altered synaptic plasticity, and decreased synaptic transmission. Recent studies indicate N-methyl-d-aspartate and ryanodine receptors and Ca2+ signaling molecules as molecular substrates of redox-mediated senescent physiology. CRITICAL ISSUES We review redox homeostasis mechanisms and consider the chemical character of reactive oxygen and nitrogen species and their role in regulating different transmitter systems. In this regard, senescent physiology may represent the co-opting of pathways normally responsible for feedback regulation of synaptic transmission. Furthermore, differences across transmitter systems may underlie differential vulnerability of brain regions and neuronal circuits to aging and disease. FUTURE DIRECTIONS It will be important to identify the intrinsic mechanisms for the shift in oxidative/reductive processes. Intrinsic mechanism will depend on the transmitter system, oxidative stressors, and expression/activity of antioxidant enzymes. In addition, it will be important to identify how intrinsic processes interact with other aging factors, including changes in inflammatory or hormonal signals. Antioxid. Redox Signal. 28, 1724-1745.
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Affiliation(s)
- Ashok Kumar
- 1 Department of Neuroscience, McKnight Brain Institute, University of Florida , Gainesville, Florida
| | - Brittney Yegla
- 1 Department of Neuroscience, McKnight Brain Institute, University of Florida , Gainesville, Florida
| | - Thomas C Foster
- 1 Department of Neuroscience, McKnight Brain Institute, University of Florida , Gainesville, Florida.,2 Genetics and Genomics Program, Genetics Institute, University of Florida , Gainesville, Florida
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Lester AW, Moffat SD, Wiener JM, Barnes CA, Wolbers T. The Aging Navigational System. Neuron 2017; 95:1019-1035. [PMID: 28858613 PMCID: PMC5659315 DOI: 10.1016/j.neuron.2017.06.037] [Citation(s) in RCA: 209] [Impact Index Per Article: 29.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2017] [Revised: 06/20/2017] [Accepted: 06/22/2017] [Indexed: 12/17/2022]
Abstract
The discovery of neuronal systems dedicated to computing spatial information, composed of functionally distinct cell types such as place and grid cells, combined with an extensive body of human-based behavioral and neuroimaging research has provided us with a detailed understanding of the brain's navigation circuit. In this review, we discuss emerging evidence from rodents, non-human primates, and humans that demonstrates how cognitive aging affects the navigational computations supported by these systems. Critically, we show 1) that navigational deficits cannot solely be explained by general deficits in learning and memory, 2) that there is no uniform decline across different navigational computations, and 3) that navigational deficits might be sensitive markers for impending pathological decline. Following an introduction to the mechanisms underlying spatial navigation and how they relate to general processes of learning and memory, the review discusses how aging affects the perception and integration of spatial information, the creation and storage of memory traces for spatial information, and the use of spatial information during navigational behavior. The closing section highlights the clinical potential of behavioral and neural markers of spatial navigation, with a particular emphasis on neurodegenerative disorders.
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Affiliation(s)
- Adam W Lester
- Evelyn F. McKnight Brain Institute, University of Arizona, Tucson, AZ 85721, USA; Division of Neural Systems, Memory and Aging, University of Arizona, Tucson, AZ 85721, USA
| | - Scott D Moffat
- School of Psychology, Georgia Institute of Technology, Atlanta, GA 30332 USA
| | - Jan M Wiener
- Department of Psychology, Ageing and Dementia Institute, Bournemouth University, Poole BH12 5BB, UK
| | - Carol A Barnes
- Evelyn F. McKnight Brain Institute, University of Arizona, Tucson, AZ 85721, USA; Division of Neural Systems, Memory and Aging, University of Arizona, Tucson, AZ 85721, USA; Departments of Psychology, Neurology, and Neuroscience, University of Arizona, Tucson, AZ 85721, USA
| | - Thomas Wolbers
- German Center for Neurodegenerative Diseases (DZNE), Aging and Cognition Research Group, 39120 Magdeburg, Germany; Center for Behavioral Brain Sciences (CBBS), 39118 Magdeburg, Germany.
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Lu C, Shi Z, Sun X, Pan R, Chen S, Li Y, Qu L, Sun L, Dang H, Bu L, Chen L, Liu X. Kai Xin San aqueous extract improves Aβ 1-40-induced cognitive deficits on adaptive behavior learning by enhancing memory-related molecules expression in the hippocampus. JOURNAL OF ETHNOPHARMACOLOGY 2017; 201:73-81. [PMID: 27751826 DOI: 10.1016/j.jep.2016.10.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2015] [Revised: 09/18/2016] [Accepted: 10/03/2016] [Indexed: 06/06/2023]
Abstract
ETHNOPHARMACOLOGICAL RELEVANCE Kai Xin San (KXS), a traditional formula of Chinese medicine, has been used to treat dementia. AIM OF THE STUDY The present study aimed to investigate its ameliorating effects on Aβ1-40-induced cognitive impairment in rats using a series of novel reward-directed instrumental learning tasks, and to determine its possible mechanism of action. MATERIALS AND METHODS Rats were pretreated with KXS aqueous extract (0.72 and 1.44g/kg, p.o.) for 10 days, and were trained to gain reward reinforcement by lever pressing at the meantime. Thereafter, rats received a bilateral microinjection of Aβ1-40 in CA1 regions of the hippocampus. Cognitive performance was evaluated with the goal directed (higher response ratio) and habit (visual signal discrimination and extinction) learning tasks, as well as on the levels of memory-related biochemical parameters and molecules. RESULTS Our findings first demonstrated that KXS can improve Aβ1-40-induced amnesia in RDIL via enhancing the comprehension of action-outcome association and the utilization of cue information to guide behavior. Then, its ameliorating effects should be attributed to the modulation of memory-related molecules in the hippocampus. CONCLUSION In conclusion, KXS has the potential to prevent and/or delay the deterioration of cognitive impairment in AD.
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Affiliation(s)
- Cong Lu
- Research Center for Pharmacology & Toxicology, Institute of Medicinal Plant Development (IMPLAD), Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China.
| | - Zhe Shi
- Research Center for Pharmacology & Toxicology, Institute of Medicinal Plant Development (IMPLAD), Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Xiuping Sun
- Research Center for Pharmacology & Toxicology, Institute of Medicinal Plant Development (IMPLAD), Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Ruile Pan
- Research Center for Pharmacology & Toxicology, Institute of Medicinal Plant Development (IMPLAD), Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Shanguang Chen
- China Astronaut Research and Training Center, Beijing, China
| | - Yinghui Li
- China Astronaut Research and Training Center, Beijing, China
| | - Lina Qu
- China Astronaut Research and Training Center, Beijing, China
| | - Lihua Sun
- Chinese Academy of Chinese Medical Sciences, Beijing, China
| | - Haixia Dang
- Chinese Academy of Chinese Medical Sciences, Beijing, China
| | - Lanlan Bu
- Hunan University of Traditional Chinese Medicine, Changsha, Hunan, China
| | - Lingling Chen
- Hunan University of Traditional Chinese Medicine, Changsha, Hunan, China
| | - Xinmin Liu
- Research Center for Pharmacology & Toxicology, Institute of Medicinal Plant Development (IMPLAD), Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China; Hunan University of Traditional Chinese Medicine, Changsha, Hunan, China.
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Zhao R, Grunke SD, Keralapurath MM, Yetman MJ, Lam A, Lee TC, Sousounis K, Jiang Y, Swing DA, Tessarollo L, Ji D, Jankowsky JL. Impaired Recall of Positional Memory following Chemogenetic Disruption of Place Field Stability. Cell Rep 2016; 16:793-804. [PMID: 27373150 PMCID: PMC4956499 DOI: 10.1016/j.celrep.2016.06.032] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2015] [Revised: 03/03/2016] [Accepted: 06/03/2016] [Indexed: 11/06/2022] Open
Abstract
The neural network of the temporal lobe is thought to provide a cognitive map of our surroundings. Functional analysis of this network has been hampered by coarse tools that often result in collateral damage to other circuits. We developed a chemogenetic system to temporally control electrical input into the hippocampus. When entorhinal input to the perforant path was acutely silenced, hippocampal firing patterns became destabilized and underwent extensive remapping. We also found that spatial memory acquired prior to neural silencing was impaired by loss of input through the perforant path. Together, our experiments show that manipulation of entorhinal activity destabilizes spatial coding and disrupts spatial memory. Moreover, we introduce a chemogenetic model for non-invasive neuronal silencing that offers multiple advantages over existing strategies in this setting.
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Affiliation(s)
- Rong Zhao
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA
| | - Stacy D Grunke
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA
| | | | - Michael J Yetman
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA
| | - Alexander Lam
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA; Department of Cognitive Science, Rice University, Houston, TX 77251, USA
| | - Tang-Cheng Lee
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA
| | | | - Yongying Jiang
- Institute for Applied Cancer Science, The University of Texas MD Anderson Cancer Center, Houston, TX 77054, USA
| | - Deborah A Swing
- Mouse Cancer Genetics Program, Center for Cancer Research, National Cancer Institute, Frederick, MD 21702, USA
| | - Lino Tessarollo
- Mouse Cancer Genetics Program, Center for Cancer Research, National Cancer Institute, Frederick, MD 21702, USA
| | - Daoyun Ji
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA; Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX 77030, USA.
| | - Joanna L Jankowsky
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA; Department of Neurology, Baylor College of Medicine, Houston, TX 77030, USA; Department of Neurosurgery, Baylor College of Medicine, Houston, TX 77030, USA; Huffington Center on Aging, Baylor College of Medicine, Houston, TX 77030, USA.
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Febo M, Foster TC. Preclinical Magnetic Resonance Imaging and Spectroscopy Studies of Memory, Aging, and Cognitive Decline. Front Aging Neurosci 2016; 8:158. [PMID: 27468264 PMCID: PMC4942756 DOI: 10.3389/fnagi.2016.00158] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2016] [Accepted: 06/16/2016] [Indexed: 01/14/2023] Open
Abstract
Neuroimaging provides for non-invasive evaluation of brain structure and activity and has been employed to suggest possible mechanisms for cognitive aging in humans. However, these imaging procedures have limits in terms of defining cellular and molecular mechanisms. In contrast, investigations of cognitive aging in animal models have mostly utilized techniques that have offered insight on synaptic, cellular, genetic, and epigenetic mechanisms affecting memory. Studies employing magnetic resonance imaging and spectroscopy (MRI and MRS, respectively) in animal models have emerged as an integrative set of techniques bridging localized cellular/molecular phenomenon and broader in vivo neural network alterations. MRI methods are remarkably suited to longitudinal tracking of cognitive function over extended periods permitting examination of the trajectory of structural or activity related changes. Combined with molecular and electrophysiological tools to selectively drive activity within specific brain regions, recent studies have begun to unlock the meaning of fMRI signals in terms of the role of neural plasticity and types of neural activity that generate the signals. The techniques provide a unique opportunity to causally determine how memory-relevant synaptic activity is processed and how memories may be distributed or reconsolidated over time. The present review summarizes research employing animal MRI and MRS in the study of brain function, structure, and biochemistry, with a particular focus on age-related cognitive decline.
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Affiliation(s)
- Marcelo Febo
- Department of Psychiatry, William L. and Evelyn F. McKnight Brain Institute, University of Florida Gainesville, FL, USA
| | - Thomas C Foster
- Department of Neuroscience, William L. and Evelyn F. McKnight Brain Institute, University of Florida Gainesville, FL, USA
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Shi Z, Lu C, Sun X, Wang Q, Chen S, Li Y, Qu L, Chen L, Bu L, Liao D, Liu X. Tong Luo Jiu Nao ameliorates Aβ1-40-induced cognitive impairment on adaptive behavior learning by modulating ERK/CaMKII/CREB signaling in the hippocampus. Altern Ther Health Med 2015; 15:55. [PMID: 25888276 PMCID: PMC4380248 DOI: 10.1186/s12906-015-0584-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2014] [Accepted: 02/21/2015] [Indexed: 12/25/2022]
Abstract
BACKGROUND Tong Luo Jiu Nao (TLJN), a modern formula of Chinese medicine extracts on the basis of Traditional Chinese Medicine theory, has been used to treat dementia. The present study aimed to investigate its ameliorating effects on Aβ1-40-induced cognitive impairment in rats using a series of novel reward-directed instrumental learning (RDIL) tasks, and to determine its possible mechanism of action. METHODS Rats were pretreated with TLJN extract (0.9 and 1.8 g/kg, p.o.) for 10 daysbefore surgery, and were trained to gain reward reinforcement by lever pressing at the meantime. Thereafter, rats received a bilateral microinjection of Aβ1-40 in CA1 regions of the hippocampus. Cognitive performance was evaluated with the goal directed (higher response ratio) and habit (visual signal discrimination and extinction) learning tasks, as well as on the levels of biochemical parameters and molecules. RESULTS Our findings first demonstrated that TLJN can improve Aβ1-40-induced amnesia in RDIL via enhancing the comprehension of action-outcome association and the utilization of cue information to guide behavior. Then, its ameliorating effects should attribute to the modulation of ERK/CaMKII/CREB signaling in the hippocampus. CONCLUSION TLJN can markedly enhance cognitions of Aβ1-40 microinjection animal model in adaptive behavioral tasks. It has the potential, possibly as complementary and alternative therapy, to prevent and/or delay the deterioration of cognitive impairment in AD.
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10
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Lee I, Lee CH. Contextual behavior and neural circuits. Front Neural Circuits 2013; 7:84. [PMID: 23675321 PMCID: PMC3650478 DOI: 10.3389/fncir.2013.00084] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2013] [Accepted: 04/14/2013] [Indexed: 11/13/2022] Open
Abstract
Animals including humans engage in goal-directed behavior flexibly in response to items and their background, which is called contextual behavior in this review. Although the concept of context has long been studied, there are differences among researchers in defining and experimenting with the concept. The current review aims to provide a categorical framework within which not only the neural mechanisms of contextual information processing but also the contextual behavior can be studied in more concrete ways. For this purpose, we categorize contextual behavior into three subcategories as follows by considering the types of interactions among context, item, and response: contextual response selection, contextual item selection, and contextual item–response selection. Contextual response selection refers to the animal emitting different types of responses to the same item depending on the context in the background. Contextual item selection occurs when there are multiple items that need to be chosen in a contextual manner. Finally, when multiple items and multiple contexts are involved, contextual item–response selection takes place whereby the animal either chooses an item or inhibits such a response depending on item–context paired association. The literature suggests that the rhinal cortical regions and the hippocampal formation play key roles in mnemonically categorizing and recognizing contextual representations and the associated items. In addition, it appears that the fronto-striatal cortical loops in connection with the contextual information-processing areas critically control the flexible deployment of adaptive action sets and motor responses for maximizing goals. We suggest that contextual information processing should be investigated in experimental settings where contextual stimuli and resulting behaviors are clearly defined and measurable, considering the dynamic top-down and bottom-up interactions among the neural systems for contextual behavior.
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Affiliation(s)
- Inah Lee
- Behavioral Neurophysiology Laboratory, Department of Brain and Cognitive Sciences, Seoul National University Seoul, South Korea
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11
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Jacobson TK, Howe MD, Schmidt B, Hinman JR, Escabí MA, Markus EJ. Hippocampal theta, gamma, and theta-gamma coupling: effects of aging, environmental change, and cholinergic activation. J Neurophysiol 2013; 109:1852-65. [PMID: 23303862 DOI: 10.1152/jn.00409.2012] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Hippocampal theta and gamma oscillations coordinate the timing of multiple inputs to hippocampal neurons and have been linked to information processing and the dynamics of encoding and retrieval. One major influence on hippocampal rhythmicity is from cholinergic afferents. In both humans and rodents, aging is linked to impairments in hippocampus-dependent function along with degradation of cholinergic function. Cholinomimetics can reverse some age-related memory impairments and modulate oscillations in the hippocampus. Therefore, one would expect corresponding changes in these oscillations and possible rescue with the cholinomimetic physostigmine. Hippocampal activity was recorded while animals explored a familiar or a novel maze configuration. Reexposure to a familiar situation resulted in minimal aging effects or changes in theta or gamma oscillations. In contrast, exploration of a novel maze configuration increased theta power; this was greater in adult than old animals, although the deficit was reversed with physostigmine. In contrast to the theta results, the effects of novelty, age, and/or physostigmine on gamma were relatively weak. Unrelated to the behavioral situation were an age-related decrease in the degree of theta-gamma coupling and the fact that physostigmine lowered the frequency of theta in both adult and old animals. The results indicate that age-related changes in gamma and theta modulation of gamma, while reflecting aging changes in hippocampal circuitry, seem less related to aging changes in information processing. In contrast, the data support a role for theta and the cholinergic system in encoding and that hippocampal aging is related to impaired encoding of new information.
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Affiliation(s)
- Tara K Jacobson
- Dept. of Psychology, Behavioral Neuroscience, Univ. of Connecticut, Storrs, CT 06269, USA
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12
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Shi Z, Sun X, Liu X, Chen S, Chang Q, Chen L, Song G, Li H. Evaluation of an Aβ1–40-induced cognitive deficit in rat using a reward-directed instrumental learning task. Behav Brain Res 2012; 234:323-33. [DOI: 10.1016/j.bbr.2012.07.006] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2012] [Revised: 07/03/2012] [Accepted: 07/06/2012] [Indexed: 01/04/2023]
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13
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Penner MR, Mizumori SJY. Age-associated changes in the hippocampal-ventral striatum-ventral tegmental loop that impact learning, prediction, and context discrimination. Front Aging Neurosci 2012; 4:22. [PMID: 22891060 PMCID: PMC3413901 DOI: 10.3389/fnagi.2012.00022] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2012] [Accepted: 07/23/2012] [Indexed: 11/13/2022] Open
Abstract
Studies of the neural mechanisms of navigation and context discrimination have generated a powerful heuristic for understanding how neural codes, circuits, and computations contribute to accurate behavior as animals traverse and learn about spatially extended environments. It is assumed that memories are updated as a result of spatial experience. The mechanism, however, for such a process is not clear. Here we suggest that one revealing approach to study this issue is to integrate our knowledge about limbic system mediated navigation and context discrimination with knowledge about how midbrain neural circuitry mediates decision-making. This perspective should lead to new and specific neural theories about how choices that we make during navigation determine what information is ultimately learned and remembered. This same circuitry may be involved when past experiences come to bias future spatial perceptions and response selection. With old age come not only important changes in limbic system operations, but also significant decline in the function of midbrain regions that underlie accurate and efficient decisions. Thus, suboptimal accuracy of spatial context-based decision-making may be, at least in part, responsible for the common observation of spatial memory decline in old age.
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Affiliation(s)
- Marsha R Penner
- Laboratory of Neural Systems, Decision Science, Learning and Memory, Department of Psychology, University of Washington Seattle, WA, USA
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14
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Huxter JR, Miranda JA, Dias R. The hippocampal physiology of approaching middle-age: early indicators of change. Hippocampus 2012; 22:1923-40. [PMID: 22674542 DOI: 10.1002/hipo.22027] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/20/2012] [Indexed: 12/24/2022]
Abstract
Age-related cognitive decline presents serious lifestyle challenges, and anatomical changes to the hippocampus are often implicated in clinical conditions later in life. However, relatively little is known about how hippocampal physiology is altered in the transition to middle-age, when early detection may offer the best opportunity for successful treatment. High-yield extracellular recording is a powerful tool for understanding brain function in freely moving animals at single-cell resolution and with millisecond precision. We used this technique to characterize changes to hippocampal physiology associated with maturation in 35-week-old rats. Combining a series of behavioral tasks with recordings of large numbers of neurons, local field potentials (LFP), and network patterns of activation, we were able to generate a comprehensive picture based on more than 25 different assays for each subject. Notable changes associated with aging included increased firing rates in interneurons, reduced LFP power but increased frequency in the 4-12 Hz theta band, and impairment in hippocampal pattern-separation for different environments. General properties of pyramidal cell firing and spatial map integrity were preserved. There was no impairment in theta phase-precession, experience-dependent place field expansion, or sleep reactivation of waking network patterns. There were however changes in foraging strategy and behavioral responses to the introduction of a novel environment. Taken together the results reveal a diverse pattern of changes which are of increasing relevance in an aging population. They also highlight areas where high-yield electrophysiological assays can be used to provide the sensitivity and throughput required for pre-clinical drug-discovery programs.
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Affiliation(s)
- John R Huxter
- Neusentis, Pfizer Ltd., The Portway Building, Granta Park, Great Abington, United Kingdom.
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15
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Schmidt B, Satvat E, Argraves M, Markus EJ, Marrone DF. Cognitive demands induce selective hippocampal reorganization: Arc expression in a place and response task. Hippocampus 2012; 22:2114-26. [PMID: 22573703 DOI: 10.1002/hipo.22031] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/26/2012] [Indexed: 01/11/2023]
Abstract
Place cells in the hippocampus can maintain multiple representations of a single environment and respond to physical and/or trajectory changes by remapping. Within the hippocampus there are anatomical, electrophysiological, and behavioral dissociations between the dorsal and ventral hippocampus and within dorsal CA1. Arc expression was used to measure the recruitment of ensembles across different hippocampal subregions in rats trained to utilize two different cognitive strategies while traversing an identical trajectory. This behavioral paradigm allowed for the measurement of remapping in the absence of changes in external cues, trajectory traversed (future/past), running speed, motivation, or different stages of learning. Changes in task demands induced remapping in only some hippocampal regions: reorganization of cell ensembles was observed in dorsal CA1 but not in dorsal CA3. Moreover, a gradient was found in the degree of remapping within dorsal CA1 that corresponds to entorhinal connectivity to this region. Remapping was not seen in the ventral hippocampus: neither ventral CA1 nor CA3 exhibited ensemble changes with different cognitive demands. This contrasts with findings of remapping in both the dorsal and ventral dentate gyrus using this task. The results suggest that the dorsal pole of the hippocampus is more sensitive to changes in task demands.
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Affiliation(s)
- Brandy Schmidt
- Dept. of Psychology, University of Connecticut, Storrs, Connecticut, USA
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16
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Rosiglitazone enhances learning, place cell activity, and synaptic plasticity in middle-aged rats. Neurobiol Aging 2012; 33:835.e13-30. [DOI: 10.1016/j.neurobiolaging.2011.08.013] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2010] [Revised: 07/26/2011] [Accepted: 08/18/2011] [Indexed: 11/23/2022]
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17
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Vetreno RP, Ramos RL, Anzalone S, Savage LM. Brain and behavioral pathology in an animal model of Wernicke's encephalopathy and Wernicke-Korsakoff Syndrome. Brain Res 2012; 1436:178-92. [PMID: 22192411 PMCID: PMC3266665 DOI: 10.1016/j.brainres.2011.11.038] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2011] [Revised: 11/16/2011] [Accepted: 11/18/2011] [Indexed: 01/24/2023]
Abstract
Animal models provide the opportunity for in-depth and experimental investigation into the anatomical and physiological underpinnings of human neurological disorders. Rodent models of thiamine deficiency have yielded significant insight into the structural, neurochemical and cognitive deficits associated with thiamine deficiency as well as proven useful toward greater understanding of memory function in the intact brain. In this review, we discuss the anatomical, neurochemical and behavioral changes that occur during the acute and chronic phases of thiamine deficiency and describe how rodent models of Wernicke-Korsakoff Syndrome aid in developing a more detailed picture of brain structures involved in learning and memory.
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Affiliation(s)
- Ryan P. Vetreno
- Behavioral Neuroscience Program, Department of Psychology, State University of New York at Binghamton, Binghamton, NY 13902
| | - Raddy L. Ramos
- Department of Neuroscience & Histology, New York College of Osteopathic Medicine, New York Institute of Technology, Old Westbury NY 11568
| | - Steven Anzalone
- Behavioral Neuroscience Program, Department of Psychology, State University of New York at Binghamton, Binghamton, NY 13902
| | - Lisa M. Savage
- Behavioral Neuroscience Program, Department of Psychology, State University of New York at Binghamton, Binghamton, NY 13902
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18
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Maasberg DW, Shelley LE, Gilbert PE. Age-related changes in detection of spatial novelty. Behav Brain Res 2011; 228:447-51. [PMID: 22203158 DOI: 10.1016/j.bbr.2011.12.024] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2011] [Revised: 11/08/2011] [Accepted: 12/14/2011] [Indexed: 11/25/2022]
Abstract
Age-related changes in novelty detection for object-place associations was assessed in 6-mo and 25-mo-old Fisher 344/Brown Norway (F344/BN) rats. Old rats showed significant deficits compared to young rats in detecting spatial displacement of objects. The data suggest that object-place novelty detection is impaired in aged F344/BN rats using a rapidly acquired, exploratory-based task. The results may have important implications for the selection of efficient memory paradigms for future aging studies.
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Affiliation(s)
- David W Maasberg
- Department of Psychology, San Diego State University, 5500 Campanile Dr., San Diego, CA 92182, United States
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19
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Poucet B, Hok V, Sargolini F, Save E. Stability and variability of place cell activity during behavior: functional implications for dynamic coding of spatial information. ACTA ACUST UNITED AC 2011; 106:62-71. [PMID: 21930204 DOI: 10.1016/j.jphysparis.2011.09.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2011] [Revised: 07/25/2011] [Accepted: 09/02/2011] [Indexed: 11/18/2022]
Abstract
In addition to their discharge strongly related to a rat's location in the environment, hippocampal place cells have recently been discovered to carry other more subtle signals. For instance, place cells exhibit overdispersion, i.e., a tendency to have highly variable firing rates across successive passes in the firing field, which may reflect the processing of different classes of cues. In addition, the place cell population tends to fire synchronously during specific phases of place navigation, presumably signaling the animal's arrival at the goal location, or to be reactivated during either sleep or wakefulness following exposure to a new environment, a process thought to be important for memory consolidation. Although these various phenomena are expressed at different timescales, it is very likely that they can occur at the same time during an animal's exposure to a spatial environment. The advantage of such simultaneous processing is that it permits the organism both to be aware of its own location in the environment, and to attend to other environmental features and to store multiple experiences. However its pitfall is that it may result in noisy signals that are difficult to decipher by output structures. Therefore the question is asked of how the information carried by each process can be disentangled. We provide some examples from recent research work showing that this problem is far from being trivial and we propose an explanatory framework in which place cell activity at different timescales could be viewed as a series of dynamic attractors nested within each other.
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Affiliation(s)
- B Poucet
- Laboratory of Neurobiology and Cognition, CNRS - Université de Provence, Marseille, France.
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20
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Burger C. Region-specific genetic alterations in the aging hippocampus: implications for cognitive aging. Front Aging Neurosci 2010; 2:140. [PMID: 21048902 PMCID: PMC2967426 DOI: 10.3389/fnagi.2010.00140] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2010] [Accepted: 08/17/2010] [Indexed: 01/31/2023] Open
Abstract
Aging is associated with cognitive decline in both humans and animals and of all brain regions, the hippocampus appears to be particularly vulnerable to senescence. Age-related spatial learning deficits result from alterations in hippocampal connectivity and plasticity. These changes are differentially expressed in each of the hippocampal fields known as cornu ammonis 1 (CA1), cornu ammonis 3 (CA3), and the dentate gyrus. Each sub-region displays varying degrees of susceptibility to aging. For example, the CA1 region is particularly susceptible in Alzheimer's disease while the CA3 region shows vulnerability to stress and glucocorticoids. Further, in animals, aging is the main factor associated with the decline in adult neurogenesis in the dentate gyrus. This review discusses the relationship between region-specific hippocampal connectivity, morphology, and gene expression alterations and the cognitive deficits associated with senescence. In particular, data are reviewed that illustrate how the molecular changes observed in the CA1, CA3, and dentate regions are associated with age-related learning deficits. This topic is of importance because increased understanding of how gene expression patterns reflect individual differences in cognitive performance is critical to the process of identifying new and clinically useful biomarkers for cognitive aging.
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Affiliation(s)
- Corinna Burger
- Department of Neurology, Medical Sciences Center, University of WisconsinMadison, USA
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21
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Age-related increase of sI(AHP) in prefrontal pyramidal cells of monkeys: relationship to cognition. Neurobiol Aging 2010; 33:1085-95. [PMID: 20727620 DOI: 10.1016/j.neurobiolaging.2010.07.002] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2010] [Revised: 06/23/2010] [Accepted: 07/05/2010] [Indexed: 01/26/2023]
Abstract
Reduced excitability, due to an increase in the slow afterhyperpolarization (and its underlying current sI(AHP)), occurs in CA1 pyramidal cells in aged cognitively-impaired, but not cognitively-unimpaired, rodents. We sought to determine whether similar age-related changes in the sI(AHP) occur in pyramidal cells in the rhesus monkey dorsolateral prefrontal cortex (dlPFC). Whole-cell patch-clamp recordings were obtained from layer 3 and layer 5 pyramidal cells in dlPFC slices prepared from young (9.6 ± 0.7 years old) and aged (22.3 ± 0.7 years old) behaviorally characterized subjects. The amplitude of the sI(AHP) was significantly greater in layer 3 (but not layer 5) cells from aged-impaired compared with both aged-unimpaired and young monkeys, which did not differ. Aged layer 3, but not layer 5, cells exhibited significantly increased action potential firing rates, but there was no relationship between sI(AHP) and firing rate. Thus, in monkey dlPFC layer 3 cells, an increase in sI(AHP) is associated with age-related cognitive decline; however, this increase is not associated with a reduction in excitability.
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22
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Burke SN, Maurer AP, Yang Z, Navratilova Z, Barnes CA. Glutamate receptor-mediated restoration of experience-dependent place field expansion plasticity in aged rats. Behav Neurosci 2008; 122:535-48. [PMID: 18513124 DOI: 10.1037/0735-7044.122.3.535] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Place fields of hippocampal pyramidal cells expand asymmetrically when adult rats repeatedly follow the same route. This behaviorally induced expression of neuronal plasticity uses an NMDAR-dependent, LTP-like mechanism and could be used by hippocampal networks to store information. Aged spatial memory-impaired rats exhibit defective experience-dependent place field expansion plasticity. One possible explanation for this aged-associated deficit is alterations in glutamatergic function. In fact, both NMDAR- and AMPAR-mediated field excitatory postsynaptic potentials in CA1 decrease with aging. The current study investigated whether modulation of either AMPA or NDMA receptor activity could restore this experience-dependent plasticity by prolonging AMPAR activity with the ampakine CX516 and modulating the NMDAR with the noncompetitive antagonist memantine. The spatial firing characteristics of multiple CA1 pyramidal cells were monitored under both treatment conditions as aged rats repeatedly traversed a circular track. Compared to the saline baseline condition, acute administration of memantine, but not CX516, reinstated experience-dependent place field expansion. Taken together, these data suggest that pharmacological manipulation of the NMDAR can improve the function of hippocampal networks critical to optimal cognition in aging.
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Affiliation(s)
- Sara N Burke
- Evelyn F. McKnight Brain Institute, Life Sciences North Building, Room 384, University of Arizona, Tucson, AZ 85724, USA
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23
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Oler JA, Penley SC, Sava S, Markus EJ. Does the dorsal hippocampus process navigational routes or behavioral context? A single-unit analysis. Eur J Neurosci 2008; 28:802-12. [DOI: 10.1111/j.1460-9568.2008.06375.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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24
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Sava S, Markus EJ. Activation of the medial septum reverses age-related hippocampal encoding deficits: a place field analysis. J Neurosci 2008; 28:1841-53. [PMID: 18287501 PMCID: PMC6671449 DOI: 10.1523/jneurosci.4629-07.2008] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2007] [Revised: 12/12/2007] [Accepted: 12/31/2007] [Indexed: 11/21/2022] Open
Abstract
When a rat runs through a familiar environment, the hippocampus retrieves a previously stored spatial representation of the environment. When the environment is modified a new representation is seen, presumably corresponding to the hippocampus encoding the new information. The medial septum is hypothesized to modulate whether the hippocampus engages in retrieval or encoding. The cholinergic agonist carbachol was infused into the medial septum, and hippocampal CA1 place cells were recorded in freely moving rats. In a familiar environment, septal activation impaired the retrieval of a previously stored hippocampal place cell representation regardless of age. When the environment was changed, medial septal activation impaired the encoding process in young, but facilitated the encoding of the new information in aged rats. Moreover, the improved encoding was evident during a subsequent exposure to the modified environment 24 h later. The findings support the role the septum plays in modulating hippocampal retrieval/encoding states. Furthermore, our data indicate a mechanism of age-related cognitive impairment.
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Affiliation(s)
- Simona Sava
- Behavioral Neuroscience Division, Department of Psychology, University of Connecticut, Storrs, Connecticut 06269, and
- Department of Psychiatry, Harvard Medical School and Brain Imaging Center, McLean Hospital, Belmont, Massachusetts 02478
| | - Etan J. Markus
- Behavioral Neuroscience Division, Department of Psychology, University of Connecticut, Storrs, Connecticut 06269, and
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25
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The relationship between the field-shifting phenomenon and representational coherence of place cells in CA1 and CA3 in a cue-altered environment. Learn Mem 2007; 14:807-15. [PMID: 18007023 DOI: 10.1101/lm.706207] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Subfields of the hippocampus display differential dynamics in processing a spatial environment, especially when changes are introduced to the environment. Specifically, when familiar cues in the environment are spatially rearranged, place cells in the CA3 subfield tend to rotate with a particular set of cues (e.g., proximal cues), maintaining a coherent spatial representation. Place cells in CA1, in contrast, display discordant behaviors (e.g., rotating with different sets of cues or remapping) in the same condition. In addition, on average, CA3 place cells shift their firing locations (measured by the center of mass, or COM) backward over time when the animal encounters the changed environment for the first time, but not after that first experience. However, CA1 displays an opposite pattern, in which place cells exhibit the backward COM-shift only from the second day of experience, but not on the first day. Here, we examined the relationship between the environment-representing behavior (i.e., rotation vs. remapping) and the COM-shift of place fields in CA1 and CA3. Both in CA1 and CA3, the backward (as well as forward) COM-shift phenomena occurred regardless of the rotating versus remapping of the place cell. The differential, daily time course of the onset/offset of backward COM-shift in the cue-altered environment in CA1 and CA3 (on day 1 in CA1 and from day 2 onward in CA3) stems from different population dynamics between the subfields. The results suggest that heterogeneous, complex plasticity mechanisms underlie the environment-representating behavior (i.e., rotate/remap) and the COM-shifting behavior of the place cell.
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26
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Luu TT, Pirogovsky E, Gilbert PE. Age-related changes in contextual associative learning. Neurobiol Learn Mem 2007; 89:81-5. [PMID: 17967551 DOI: 10.1016/j.nlm.2007.09.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2007] [Revised: 09/05/2007] [Accepted: 09/06/2007] [Indexed: 11/29/2022]
Abstract
The hippocampus plays a critical role in processing contextual information. Although age-related changes in the hippocampus are well documented in humans, nonhuman primates, and rodents, few studies have examined contextual learning deficits in old rats. The present study investigated age-related differences in contextual associative learning in young (6 mo) and old (24 mo) rats using olfactory stimuli. Stimuli consisted of common odors mixed in sand and placed in clear plastic cups. Testing was conducted in two boxes that represented two different contexts (Context 1 and Context 2). The contexts varied based on environmental features of the box such as color (black vs. white), visual cues on the walls of the box, and flooring texture. Each rat was simultaneously presented with two cups, one filled with Odor A and one filled with Odor B in each context. In Context 1, the rat received a food reward for digging in the cup containing Odor A, but did not receive a food reward for digging in the cup containing Odor B. In Context 2, the rat was rewarded for digging in the cup containing Odor B, but did receive a reward for digging in the cup containing Odor A. Therefore, the rat learned to associate Context 1 with Odor A and Context 2 with Odor B. The rat was tested for eight days using the same odor problem throughout all days of testing. The results showed no significant difference between young and old rats on the first two days of testing; however, young rats significantly outperformed old rats on Day 3. Young rats continued to maintain superior performance compared to old rats on Days 4-8. The results suggest that aging results in functional impairments in brain regions that support memory for associations between specific cues and their respective context.
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Affiliation(s)
- Trinh T Luu
- Department of Psychology, San Diego State University, San Diego, CA, USA
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27
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Wilson IA, Gallagher M, Eichenbaum H, Tanila H. Neurocognitive aging: prior memories hinder new hippocampal encoding. Trends Neurosci 2006; 29:662-70. [PMID: 17046075 PMCID: PMC2614702 DOI: 10.1016/j.tins.2006.10.002] [Citation(s) in RCA: 235] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2006] [Revised: 07/26/2006] [Accepted: 10/04/2006] [Indexed: 02/07/2023]
Abstract
Normal aging is often accompanied by impairments in forming new memories, and studies of aging rodents have revealed structural and functional changes to the hippocampus that might point to the mechanisms behind such memory loss. In this article, we synthesize recent neurobiological and neurophysiological findings into a model of the information-processing circuit of the aging hippocampus. The key point of the model is that small concurrent changes during aging strengthen the auto-associative network of the CA3 subregion at the cost of processing new information coming in from the entorhinal cortex. As a result of such reorganization in aged memory-impaired individuals, information that is already stored would become the dominant pattern of the hippocampus to the detriment of the ability to encode new information.
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Affiliation(s)
- Iain A Wilson
- Department of Neuroscience and Neurology, University of Kuopio, Kuopio 70211, Finland.
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28
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Tropp Sneider J, Chrobak JJ, Quirk MC, Oler JA, Markus EJ. Differential behavioral state-dependence in the burst properties of CA3 and CA1 neurons. Neuroscience 2006; 141:1665-77. [PMID: 16843607 DOI: 10.1016/j.neuroscience.2006.05.052] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2006] [Revised: 05/15/2006] [Accepted: 05/16/2006] [Indexed: 01/07/2023]
Abstract
Brief bursts of fast high-frequency action potentials are a signature characteristic of CA3 and CA1 pyramidal neurons. Understanding the factors determining burst and single spiking is potentially significant for sensory representation, synaptic plasticity and epileptogenesis. A variety of models suggest distinct functional roles for burst discharge, and for specific characteristics of the burst in neural coding. However, little in vivo data demonstrate how often and under what conditions CA3 and CA1 actually exhibit burst and single spike discharges. The present study examined burst discharge and single spiking of CA3 and CA1 neurons across distinct behavioral states (awake-immobility and maze-running) in rats. In both CA3 and CA1 spike bursts accounted for less than 20% of all spike events. CA3 neurons exhibited more spikes per burst, greater spike frequency, larger amplitude spikes and more spike amplitude attenuation than CA1 neurons. A major finding of the present study is that the propensity of CA1 neurons to burst was affected by behavioral state, while the propensity of CA3 to burst was not. CA1 neurons exhibited fewer bursts during maze running compared with awake-immobility. In contrast, there were no differences in burst discharge of CA3 neurons. Neurons in both subregions exhibited smaller spike amplitude, fewer spikes per burst, longer inter-spike intervals and greater spike amplitude attenuation within a burst during awake-immobility compared with maze running. These findings demonstrate that the CA1 network is under greater behavioral state-dependent regulation than CA3. The present findings should inform both theoretic and computational models of CA3 and CA1 function.
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Affiliation(s)
- J Tropp Sneider
- Behavioral Neuroscience Division, Department of Psychology, University of Connecticut, 406 Babbidge Road, Box U-20, Storrs, CT 06269, USA
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29
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Wilson IA, Ikonen S, Gallagher M, Eichenbaum H, Tanila H. Age-associated alterations of hippocampal place cells are subregion specific. J Neurosci 2006; 25:6877-86. [PMID: 16033897 PMCID: PMC6725350 DOI: 10.1523/jneurosci.1744-05.2005] [Citation(s) in RCA: 209] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Aging is associated with spatial memory impairments and with deficient encoding of information by the hippocampus. In young adult rats, recent studies on the firing properties of hippocampal neurons have emphasized the importance of the CA3 subregion in the rapid encoding of new spatial information. Here, we compared the spatial firing patterns of CA1 and CA3 neurons in aged memory-impaired rats with those of young rats as they explored familiar and novel environments. We found that CA1 place cells in aged and young rats had similar firing characteristics in the familiar and novel environments. In contrast, aged CA3 place cells had higher firing rates in general and failed to change their firing rates and place fields as much as CA3 cells of young rats when the rats were introduced to a novel environment. Thus, aged CA3 cells failed to rapidly encode new spatial information compared with young CA3 cells. These data suggest an important and selective contribution of CA3 dysfunction to age-related memory impairment.
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Affiliation(s)
- Iain A Wilson
- Department of Neuroscience and Neurology, University of Kuopio, Kuopio 70211, Finland.
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30
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Abstract
The mechanisms involved in plasticity in the nervous system are thought to support cognition, and some of these processes are affected during normal ageing. Notably, cognitive functions that rely on the medial temporal lobe and prefrontal cortex, such as learning, memory and executive function, show considerable age-related decline. It is therefore not surprising that several neural mechanisms in these brain areas also seem to be particularly vulnerable during the ageing process. In this review, we discuss major advances in our understanding of age-related changes in the medial temporal lobe and prefrontal cortex and how these changes in functional plasticity contribute to behavioural impairments in the absence of significant pathology.
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Affiliation(s)
- Sara N Burke
- Neural Systems, Memory, and Aging Division, Life Sciences North Building, Room 384, University of Arizona, Tucson, Arizona 85724, USA
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31
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Fuhs MC, Vanrhoads SR, Casale AE, McNaughton B, Touretzky DS. Influence of path integration versus environmental orientation on place cell remapping between visually identical environments. J Neurophysiol 2005; 94:2603-16. [PMID: 15958602 DOI: 10.1152/jn.00132.2005] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
To assess the effects of interactions between angular path integration and visual landmarks on the firing of hippocampal neurons, we recorded from CA1 pyramidal cells as rats foraged in two identical boxes with polarizing internal cues. In the same-orientation condition, following an earlier experiment by Skaggs and McNaughton, the boxes were oriented identically and connected by a corridor. In the opposite-orientation condition, the boxes were abutted by rotating them 90 degrees in opposite directions, so that their orientations differed by 180 degrees . After 16-23 days of pretraining on the same-orientation condition, three rats experienced both conditions in counterbalanced order on each of two consecutive days. On the third day they ran two opposite-orientation trials. Although Skaggs and McNaughton observed stable partial "remapping" of place fields, none of the fields in this experiment remapped in the same-orientation condition. In the opposite-orientation condition, place fields in the first box were isomorphic with those in the same-orientation condition, whereas in the second box the rats eventually exhibited completely different fields. The rats differed as to the trial in which this first occurred. Once the second box exhibited different fields, it continued to do so in all subsequent opposite-orientation trials, yet fields remained the same in subsequent same-orientation trials. The results demonstrate that when animals move actively between environments, and are thus potentially able to maintain their inertial angular orientation, discordance between environmental orientation and the rat's idiothetic direction sense can profoundly affect the hippocampal map-either immediately, or as a result of cumulative experience.
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Affiliation(s)
- Mark C Fuhs
- Department of Computer Science, Carnegie Mellon University, Pittsburgh, PA 15213-3891, USA
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32
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Tropp J, Figueiredo CM, Markus EJ. Stability of hippocampal place cell activity across the rat estrous cycle. Hippocampus 2005; 15:154-65. [PMID: 15390155 DOI: 10.1002/hipo.20042] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Findings from both in vitro and in vivo studies have shown that estrogen exerts pronounced effects on hippocampal morphology and physiology. The degree to which these molecular findings influence hippocampal processing in freely behaving animals is unclear. The present study assessed the effect of the estrous cycle on hippocampal place cells in naturally cycling rats during two behavioral states. Female Sprague-Dawley rats were trained to alternate on a U-shaped runway for food reinforcement. Single-unit recordings of hippocampal CA1 cells were conducted under two conditions: (1) at rest on a holder, and (2) running on the maze. Spatial firing characteristics of the cells were examined at different stages of the estrous cycle (i.e., diestrus, proestrus, and estrus). Specifically, information was collected on (1) mean firing rates; (2) basic place field parameters; and (3) changes in the firing dynamics of these cells (e.g., burst properties). The findings showed a decrease in mean firing rate on the maze during proestrus. However, other basic measures of spatial tuning and burst properties were unchanged. The current study suggests that there is relative stability of hippocampal place cells across the estrous cycle during a well-trained task.
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Affiliation(s)
- Jennifer Tropp
- Department of Psychology, Behavioral Neuroscience Division, University of Connecticut, Storrs, Connecticut, USA
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33
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Oler JA, Ramos RL, Penley SC, Markus EJ. Hippocampal and amygdalar involvement in discriminatory place learning. Neuroscience 2005; 132:1-12. [PMID: 15780462 DOI: 10.1016/j.neuroscience.2004.11.051] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/04/2004] [Indexed: 11/25/2022]
Abstract
A conflict task was developed that simultaneously examines place aversion learning and fear-motivated context discrimination. The task superimposed Pavlovian discriminative fear conditioning on an appetitively motivated instrumental response (alternation). Rats were trained to alternate along a high-walled, diamond-shaped runway between two chambers for food. On half of the trials, a tone CS signaled the fact that a fixed section at the apex of the runway was electrified. Both the tone and the shock were turned on at the beginning of, and remained on for the duration of, each tone trial. A new trial was initiated at the time the animal entered the subsequent food chamber. Therefore, during a tone trial, in order to attain additional food reinforcement, the animal had to cross over the electrified region at the runway apex. Behavioral performance of rats with small lesions of the amygdala or dorsal hippocampus (DH) was compared with that of sham-operated controls. All groups displayed significant discriminative responding, hesitating more on tone trials while in areas of the runway adjacent to the shock region. Animals with lesions of the DH were similar to controls with respect to the tone-mediated discrimination, yet were delayed in the initial expression of a location-specific fear response. Conversely, amygdala lesions did not affect place learning; however, these animals were impaired in their suppression of the fear response following repeated unpaired trials.
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Affiliation(s)
- J A Oler
- Behavioral Neuroscience Division, Department of Psychology, University of Connecticut, U-1020, Storrs, CT 06269, USA
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Wilson IA, Ikonen S, Gurevicius K, McMahan RW, Gallagher M, Eichenbaum H, Tanila H. Place cells of aged rats in two visually identical compartments. Neurobiol Aging 2004; 26:1099-106. [PMID: 15748790 DOI: 10.1016/j.neurobiolaging.2004.09.006] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2004] [Revised: 08/11/2004] [Accepted: 09/15/2004] [Indexed: 11/29/2022]
Abstract
Aged rats perform poorly on spatial learning tasks, a cognitive impairment which has been linked to the failure of hippocampal networks to fully encode changes in the external environment [Barnes CA, Suster MS, Shen J, McNaughton BL. Multistability of cognitive maps in the hippocampus of old rats. Nature 1997;388(6639):272-5; Wilson IA, Ikonen S, Gureviciene I, McMahan RW, Gallagher M, Eichenbaum H, et al. Cognitive aging and the hippocampus: how old rats represent new environments. J Neurosci 2004;24(15):3870-8]. To examine whether the impairment in hippocampal processing extends to conditions in which self-motion provides the cues for environmental change, we have analyzed spatial firing patterns of hippocampal pyramidal neurons in young and aged rats, as well as in young rats with selective cholinergic lesions, another model of cognitive aging. The rats walked between two visually identical environments, pitting self-motion cues that indicated environmental change against visual inputs that indicated no differences between environments. Our results indicated that place cells in both aged and cholinergic-lesioned rats were equally likely as those of young rats to create new spatial representations in the second compartment. These findings suggest that the hippocampal network of aged rats is able to process changes in internally generated cues without rigidity, but that incomplete processing of external landmark cues may lead to impaired spatial learning.
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Affiliation(s)
- Iain A Wilson
- Department of Neuroscience and Neurology, University of Kuopio, P.O. Box 1627 (Harjulantie 1), Kuopio 70211, Finland.
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Abstract
Place cells are hippocampal neurons that have a strong location-specific firing activity in the rat's current environment. Collectively, place cells also provide a signature of the rat's environment as their ensemble activity is markedly different when recorded in distinct apparatuses. This phenomenon, referred to as 'remapping', suggests that each environment activates a different hippocampal map. In this study, we sought to determine the independence of such maps. In Experiment 1, we used a cylinder apparatus that was divided into two equal halves by a central barrier with an aperture allowing the rat to freely commute between the two sides. A local change in one side failed to induce field remapping in the changed side, thus precluding any significant conclusion to be drawn. We therefore designed Experiment 2 in which place cells were first recorded while rats explored three distinct high-walled boxes. Most cells had distinctive firing fields in each box. A runway was then added to connect two initially unrelated boxes. This manipulation altered the firing of some cells but the fields in each box were still clearly distinguishable. The final manipulation consisted of changing one box and allowing the rat to commute freely between the changed and unchanged boxes. While the firing fields remapped in the changed box, they were most usually unaltered in the unchanged box. These results suggest that the hippocampus holds a set of independent maps for each box, and that each specific map is activated mainly according to the rat's current sensory environment.
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Affiliation(s)
- V Paz-Villagrán
- Laboratory of Neurobiology and Cognition (UMR 6155), Centre National de la Recherche Scientifique/Université de Provence, 31 chemin Joseph-Aiguier, 13402 Marseille cedex 20, France
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Wilson IA, Ikonen S, Gureviciene I, McMahan RW, Gallagher M, Eichenbaum H, Tanila H. Cognitive aging and the hippocampus: how old rats represent new environments. J Neurosci 2004; 24:3870-8. [PMID: 15084668 PMCID: PMC6729357 DOI: 10.1523/jneurosci.5205-03.2004] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Spatial learning impairment in aged rats is associated with changes in hippocampal connectivity and plasticity. Several studies have explored the age-related deficit in spatial information processing by recording the location-specific activity of hippocampal neurons (place cells). However, these studies have generated disparate characterizations of place cells in aged rats as unstable (Barnes et al., 1997), resistant to change (Tanila et al., 1997b; Oler and Markus, 2000; Wilson et al., 2003), or delayed in using external cues (Rosenzweig et al., 2003). To reconcile these findings, we recorded place cells from aged and young rats as they repeatedly explored both a highly familiar environment and an initially novel environment, and we repeatedly tested whether the place fields formed in the novel environment were anchored by external cues. Initially, spatial representations in aged rats were abnormally maintained between the familiar and novel environments. Then, new representations were formed but were also delayed in becoming anchored to the external landmarks. Finally, even when the new spatial representations became bound to the landmarks, they were multi-stable across repetitive exposures to the formerly novel environment. These observations help to reconcile previously divergent characterizations of spatial representation in aged rats and suggest a model of cognitive aging and hippocampal function.
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Affiliation(s)
- Iain A Wilson
- Department of Neuroscience and Neurology, University of Kuopio, Kuopio 70211, Finland.
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Jeffery KJ, Gilbert A, Burton S, Strudwick A. Preserved performance in a hippocampal-dependent spatial task despite complete place cell remapping. Hippocampus 2003; 13:175-89. [PMID: 12699326 DOI: 10.1002/hipo.10047] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The spatially localized firing of hippocampal place cells is thought to underlie the navigational function of the hippocampus. Performance on a spatial task learned using a particular place cell map should therefore deteriorate if the map is disrupted. To test this prediction, we trained rats on a hippocampal-dependent spatial task in a black box and tested them in a white box. Although the change from black to white induced remapping of most place cells, navigational performance remained essentially intact. Furthermore, place cell activity was also unrelated to specific aspects of the task such as tone onset, response, or goal location. Together, these results imply that the spatial information needed to solve this navigation task is represented outside the hippocampus and suggest that the place cells encode some other aspect, such as the spatial context.
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Abstract
Ageing is associated with learning and memory impairments. Data are reviewed that suggest that age-related impairments of hippocampal-dependent forms of memory, may be caused, in part, by altered synaptic plasticity mechanisms in the hippocampus, including long-term potentiation (LTP). To the extent that the mechanisms responsible for LTP can be understood, it may be possible to develop therapeutic approaches to alleviate memory decline in normal ageing.
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Affiliation(s)
- C A Barnes
- Departments of Psychology and Neurology, and ARL Division of Neural Systems, Memory and Aging, University of Arizona, Tucson, AZ 85724, USA.
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Wilson IA, Ikonen S, McMahan RW, Gallagher M, Eichenbaum H, Tanila H. Place cell rigidity correlates with impaired spatial learning in aged rats. Neurobiol Aging 2003; 24:297-305. [PMID: 12498963 DOI: 10.1016/s0197-4580(02)00080-5] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
In humans and in animals, some aged individuals are severely impaired in learning and memory capacity whereas others perform as well as young adults. In the present study, the spatial memory capacity of young and aged rats was characterized by the Morris water maze task, and then firing patterns of hippocampal "place cells" were assessed as the animals explored a familiar environment and a geometrically-altered version of the environment. Spatial representations of hippocampal cells in young and memory-intact aged rats changed upon exposure to the altered environment. In contrast, spatial representations of many cells in aged, memory-impaired rats were unaffected by the environmental alteration. Furthermore, combining all groups, the extent to which spatial representations distinguished the familiar and altered environments predicted learning capacity in the water maze. These findings suggest that a major component of memory impairment in aging may be the failure of the hippocampus to encode subtle differences in contextual information that differ across multiple experiences, such as the sequence of training trials in the water maze.
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Affiliation(s)
- I A Wilson
- Department of Neuroscience and Neurology, University of Kuopio, P.O. Box 1627, 70211 Kuopio, Finland.
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Rosenzweig ES, Barnes CA. Impact of aging on hippocampal function: plasticity, network dynamics, and cognition. Prog Neurobiol 2003; 69:143-79. [PMID: 12758108 DOI: 10.1016/s0301-0082(02)00126-0] [Citation(s) in RCA: 542] [Impact Index Per Article: 25.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Aging is associated with specific impairments of learning and memory, some of which are similar to those caused by hippocampal damage. Studies of the effects of aging on hippocampal anatomy, physiology, plasticity, and network dynamics may lead to a better understanding of age-related cognitive deficits. Anatomical and electrophysiological studies indicate that the hippocampus of the aged rat sustains a loss of synapses in the dentate gyrus, a loss of functional synapses in area CA1, a decrease in the NMDA-receptor-mediated response at perforant path synapses onto dentate gyrus granule cells, and an alteration of Ca(2+) regulation in area CA1. These changes may contribute to the observed age-related impairments of synaptic plasticity, which include deficits in the induction and maintenance of long-term potentiation (LTP) and lower thresholds for depotentiation and long-term depression (LTD). This shift in the balance of LTP and LTD could, in turn, impair the encoding of memories and enhance the erasure of memories, and therefore contribute to cognitive deficits experienced by many aged mammals. Altered synaptic plasticity may also change the dynamic interactions among cells in hippocampal networks, causing deficits in the storage and retrieval of information about the spatial organization of the environment. Further studies of the aged hippocampus will not only lead to treatments for age-related cognitive impairments, but may also clarify the mechanisms of learning in adult mammals.
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Affiliation(s)
- Ephron S Rosenzweig
- Arizona Research Laboratories, Division of Neural Systems, Memory, and Aging, University of Arizona, Tucson, AZ, USA
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Della-Maggiore V, Grady CL, McIntosh AR. Dissecting the effect of aging on the neural substrates of memory: deterioration, preservation or functional reorganization? Rev Neurosci 2003; 13:167-81. [PMID: 12160260 DOI: 10.1515/revneuro.2002.13.2.167] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
One of the most common deficits observed during late adulthood is a loss in the ability to learn and remember new information. This cognitive ability depends mainly on the integrity of the hippocampal formation and the prefrontal cortex, which are especially susceptible to the effects of age. Here we provide a selective review of the literature gathered from studies carried out in humans and animals, examining the effect of aging on the functional anatomy of memory. We discuss some of the methodological and theoretical difficulties associated with the current approach to the study of aging and, in turn, a series of strategies that may be implemented to ensure the most accurate interpretation of the data. Altogether, the evidence discussed in this review supports the idea that there is no general age-related deterioration of the neural substrates of memory, but rather a differential effect in which some brain areas may be adversely affected while others may compensate for the neurobiological deterioration associated with age.
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Affiliation(s)
- Valeria Della-Maggiore
- Rotman Research Institute of Baycrest Centre, Department of Psychology, University of Toronto, Ontario, Canada.
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Niño-Cabrera HG, Colin-Barenque L, Avila-Costa MR, Espinosa-Villanueva J, Fortoul TI, Rivas-Arancibia S. Differences between hippocampus and cerebral cortex in aged rats in an oxidative stress model. Int J Neurosci 2002; 112:373-81. [PMID: 12325393 DOI: 10.1080/00207450290025536] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Ozone exposure increases the production of free radicals that causes oxidative stress (OS), a state that also occurs during aging and in neurodegenerative diseases. This study identified ultrastructural alterations produced by OS induced by acute ozone exposure in hippocampus and prefrontal cortex in aged compared with young rats. Animals were exposed to 0.70 ppm ozone for 4 h, and controls to flowing air. After the exposure, the tissues were processed for ultrastructural analysis. Results showed increased ultrastructural alterations in the hippocampus and prefrontal cortex in the aged exposed animals compared with controls. OS enhanced the modifications induced by the aging process in those areas related with learning and memory functions, which are the first where degenerative aging changes are observed.
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Abstract
The purpose of the present study was to investigate the effects of sex and estrous cycle on exploratory behavior, as well as the degree to which reliance on environmental cues changes with training. Fischer 344 rats were placed three times in an open field box that contained three objects (two identical bottles and a cylinder). During the initial exposure to the environment all females showed higher activity levels and explored a larger region of the environment compared to males. However, upon subsequent exposure to the same environment, these sex differences disappeared. During the third and final session, the locations of the bottle and the cylinder were switched. The estrous females and to a lesser degree male rats, responded to the relocation of objects with a renewal of exploration and activity; proestrous females did not show this response. The rats were then trained on a four-arm radial maze reference memory task. The correct arm could be located by its relation to extra-room cues, a large distal white panel, or to local inserts on the maze. Once the animals consistently chose the goal arm, a probe session was conducted to determine which cues the animals were using to solve the task. During the probe trial both the white panel and the local inserts were rotated 90 degrees clockwise and counterclockwise respectively and the animals' choice of arm recorded. During the first probe, females tended to rely on all three types of cues in solving the task. With additional training there was a shift towards predominantly using the distal visual information. In contrast, male rats did not show this shift; by the first probe session the males were predominantly using the distal visual information to solve the task. The findings indicate: (1) sex differences in the initial use of environmental cues; (2) the usage of environmental information is dynamic and changes with additional exposures to the environment. The results are related to previous findings on sex differences and estrous cycle effects, with an emphasis on the implications for hippocampal processing.
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Affiliation(s)
- J Tropp
- Behavioral Neuroscience Division, Department of Psychology, University of Connecticut, 406 Babbidge Rd. Box U-20, Storrs, CT 06269, USA
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