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Felix Weissenberger, Hafsteinn Einarsson, Marcelo Gauy, Florian Meier, Asier Mujika, Johannes Lengler, Angelika Steger
The sharp wave ripple complex in rodent Hippocampus is associated with a network burst in CA3 (NB) that triggers a synchronous event in the CA1 population (SE). The number of CA1 pyramidal cells participating in a SE has been observed to follow a lognormal distribution. However, the origin of this skewed and heavytailed distribution of population synchrony in CA1 remains unknown. Since the size of SEs is likely to originate from the size of the NBs and the underlying neural circuitry, we model the CA3-CA1 circuit to study the underlying mechanisms and their functional implications...
July 19, 2018: Hippocampus
Jessica A Collins, Bradford C Dickerson
Activity in category selective regions of the temporal and parietal lobes during encoding has been associated with subsequent memory for face and scene stimuli. Reactivation theories of memory consolidation predict that after encoding connectivity between these category-selective regions and the hippocampus should be modulated and predict recognition memory. However, support for this proposal has been limited in humans. Here, participants completed a resting-state functional MRI (fMRI) scan, followed by face- and place-encoding tasks, followed by another resting-state fMRI scan during which they were asked to think about the stimuli they had previously encountered...
July 15, 2018: Hippocampus
Maryam Eslami, Bahman Sadeghi, Fatemeh Goshadrou
Alzheimer's disease (AD), as a common age-related dementia, is a progressive manifestation of cognitive decline following synaptic failure resulted majorly by senile plaques composed of deposits of amyloid beta (Aβ). Ghrelin is a multifunctional peptide hormone with receptors present in various brain tissues including hippocampus and has been associated with neuroprotection, neuromodulation and memory processing. Here, we investigated the neuroprotective and therapeutic effects of intracerebroventricular (icv) ghrelin infusion for two weeks on passive avoidance learning (PAL), memory retention and synaptic plasticity in the hippocampal dentate gyrus (DG) and CA1 of both normal rats and Aβ1-42-induced neurotoxicity in AD model...
July 15, 2018: Hippocampus
Molly Memel, Lee Ryan
Unitization, the process of encoding previously independent units as one coherent representation, improves associative memory in both young and older adults (Memel & Ryan, 2017; Delhaye & Bastin, 2016), or in some cases, differentially benefits older adults (Bastin et al., 2013; Ahmad et al., 2015; Zheng et al., 2015). Unitization of verbal associative pairs may reduce reliance on the hippocampus (HC) for successful encoding (Haskins et al., 2008) and recognition (Diana et al., 2011) by shifting instead to familiarity-based processing mediated by perirhinal cortex (PRC)...
July 12, 2018: Hippocampus
Pierre-Yves Jonin, Gabriel Besson, Renaud Lajoie, Jérémie Pariente, Serge Belliard, Christian Barillot, Emmanuel J Barbeau
The acquisition of new semantic memories is sometimes preserved in patients with hippocampal amnesia. Robust evidence for this comes from case reports of developmental amnesia suggesting that low-to-normal levels of semantic knowledge can be achieved despite compromised episodic learning. However, it is unclear whether this relative preservation of semantic memory results from normal acquisition and retrieval or from residual episodic memory, combined with effortful repetition. Furthermore, lesion studies have mainly focused on the hippocampus itself, and have seldom reported the state of structures in the extended hippocampal system...
July 11, 2018: Hippocampus
Kymberly C Gustus, Lu Li, Praveen Chander, Jason P Weick, Michael C Wilson, Lee Anna Cunningham
Adult neurogenesis is necessary for proper cognition and behavior, however, the mechanisms that underlie the integration and maturation of newborn neurons into the pre-existing hippocampal circuit are not entirely known. In this study, we sought to determine the role of action potential (AP)-dependent synaptic transmission by adult-generated dentate granule cells (DGCs) in their survival and function within the existing circuitry. We utilized a triple transgenic mouse (NestinCreERT2 :Snap25fl/fl : tdTomato) to inducibly inactivate AP-dependent synaptic transmission within adult hippocampal progenitors and their progeny...
July 11, 2018: Hippocampus
Melanie J Sekeres, Gordon Winocur, Morris Moscovitch, John A E Anderson, Sara Pishdadian, J Martin Wojtowicz, Marie St-Laurent, Mary Pat McAndrews, Cheryl Grady
The dynamic process of memory consolidation involves a reorganization of brain regions that support a memory trace over time, but exactly how the network reorganizes as the memory changes remains unclear. We present novel converging evidence from studies of animals (rats) and humans for the time-dependent reorganization and transformation of different types of memory as measured both by behavior and brain activation. We find that context-specific memories in rats, and naturalistic episodic memories in humans, lose precision over time and activity in the hippocampus decreases...
July 10, 2018: Hippocampus
Stephen L Cowen, Daniel T Gray, Jean-Paul L Wiegand, Lesley A Schimanski, Carol A Barnes
Hippocampal sharp-wave ripples are brief high-frequency (120 - 250 Hz) oscillatory events that support mnemonic processes during sleep and awake behavior. Although ripples occurring during sleep are believed to facilitate memory consolidation, waking ripples may also be involved in planning and memory retrieval. Recent work from our group determined that normal aging results in a significant reduction in the peak oscillatory frequency and rate-of-occurrence of ripples during sleep (Wiegand et al., 2016) that may contribute to age-associated memory decline...
July 7, 2018: Hippocampus
Charan Ranganath
Over the past 15 years, there has been an explosion of new research on the role of the hippocampus in representation of information about time in memory. Much of this work was inspired by the ideas and research of Howard Eichenbaum, who made major contributions to our understanding of the neurobiology of episodic memory and the neural representation of time. In this paper, I will review evidence regarding the role of time in understanding hippocampal function. This review will cover a broad range of evidence from studies of humans and nonhuman animals with a narrative arc that follows Howard's major discoveries...
July 6, 2018: Hippocampus
Yuguang Meng, Xiaoping Hu, Xiaodong Zhang, Jocelyne Bachevalier
Neonatal hippocampal lesions can result in long-term effects on the morphological and functional integrity of the adult brain. To investigate the effects of neonatal hippocampal lesions on the microstructural integrity of corpus callosum in adulthood, macaque monkeys (n = 5) received neonatal bilateral hippocampal lesion (Neo-Hibo) induced by infusion of ibotenic acid at 1-2 weeks of age and were scanned using diffusion tensor imaging (DTI) at 8-10 years old. Age and gender -matched control animals that had received sham operation (Neo-C, n = 5) at 1-2 weeks of age were scanned for comparison purpose...
July 6, 2018: Hippocampus
Raul Chavez-Valdez, Paul Emerson, Janasha Goffigan-Holmes, Alfredo Kirkwood, Lee J Martin, Frances J Northington
Delayed hippocampal injury and memory impairments follow neonatal hypoxia-ischemia (HI) despite the use of therapeutic hypothermia (TH). Death of hippocampal pyramidal cells occurs acutely after HI, but characterization of delayed cell death and injury of interneurons (INs) is unknown. We hypothesize that injury of INs after HI is: i) asynchronous to that of pyramidal cells, ii) independent of injury severity, and iii) unresponsive to TH. HI was induced in C57BL6 mice at p10 with unilateral right carotid ligation and 45 min of hypoxia (FiO2 =0...
May 21, 2018: Hippocampus
Blake S Porter, Robert Schmidt, David K Bilkey
Effective navigation relies on knowledge of one's environment. A challenge to effective navigation is accounting for the time and energy costs of routes. Irregular terrain in ecological environments poses a difficult navigational problem as organisms ought to avoid effortful slopes to minimize travel costs. Route planning and navigation have previously been shown to involve hippocampal place cells and their ability to encode and store information about an organism's environment. However, little is known about how place cells may encode the slope of space and associated energy costs as experiments are traditionally carried out in flat, horizontal environments...
May 21, 2018: Hippocampus
Fernanda Troyner, Maira A Bicca, Leandro J Bertoglio
The thalamic nucleus reuniens (NR) has been shown to support bidirectional medial prefrontal cortex-hippocampus communication and synchronization relevant for cognitive processing. Using non-selective or prolonged inactivation of the NR, previous studies reported its activity positively modulates aversive memory consolidation. Here we examined the NR's role in consolidating contextual fear memories with varied strength, at both recent and more remote time points, using muscimol-induced temporary inactivation in rats...
May 10, 2018: Hippocampus
Mary Youssef, Varsha S Krish, Greer S Kirshenbaum, Piray Atsak, Tamara J Lass, Sophie R Lieberman, E David Leonardo, Alex Dranovsky
Environmental exposures during early life, but not during adolescence or adulthood, lead to persistent reductions in neurogenesis in the adult hippocampal dentate gyrus (DG). The mechanisms by which early life exposures lead to long-term deficits in neurogenesis remain unclear. Here, we investigated whether targeted ablation of dividing neural stem cells during early life is sufficient to produce long-term decreases in DG neurogenesis. Having previously found that the stem cell lineage is resistant to long-term effects of transient ablation of dividing stem cells during adolescence or adulthood (Kirshenbaum et al...
May 9, 2018: Hippocampus
S C Barnett, B A L Perry, J C Dalrymple-Alford, L C Parr-Brownlie
Technology allowing genetically targeted cells to be modulated by light has revolutionised neuroscience in the past decade, and given rise to the field of optogenetic stimulation. For this, non-native, light activated proteins (e.g. channelrhodopsin) are expressed in a specific cell phenotype (e.g. glutamatergic neurons) in a subset of central nervous system nuclei, and short pulses of light of a narrow wavelength (e.g. blue, 473 nm) are used to modulate cell activity. Cell activity can be increased or decreased depending on which light activated protein is used...
May 9, 2018: Hippocampus
John C Dalrymple-Alford, Brook A L Perry
No abstract text is available yet for this article.
May 9, 2018: Hippocampus
Claire R Galloway, Kaushik Ravipati, Suyashi Singh, Evan P Lebois, Robert M Cohen, Allan I Levey, Joseph R Manns
Alzheimer's disease (AD) is a neurodegenerative disease that disproportionately impacts memory and the hippocampus. However, it is unclear how AD pathology influences the activity of surviving neurons in the hippocampus to contribute to the memory symptoms in AD. One well-understood connection between spatial memory and neuronal activity in healthy brains is the activity of place cells, neurons in the hippocampus that fire preferentially in a specific location of a given environment (the place field of the place cell)...
May 9, 2018: Hippocampus
Kenneth Kay, Loren M Frank
Contemporary brain research seeks to understand how cognition is reducible to neural activity. Crucially, much of this effort is guided by a scientific paradigm that views neural activity as essentially driven by external stimuli. In contrast, recent perspectives argue that this paradigm is by itself inadequate, and that understanding patterns of activity intrinsic to the brain is needed to explain cognition. Yet despite this critique, the stimulus-driven paradigm still dominates - possibly because a convincing alternative has not been clear...
May 3, 2018: Hippocampus
Gabriel Herrera-López, Emilio J Galván
In addition to its prominent role as an energetic substrate in the brain, lactate is emerging as a signaling molecule capable of controlling neuronal excitability. The finding that the lactate-activated receptor (hydroxycarboxylic acid receptor 1; HCA1) is widely expressed in the brain opened up the possibility that lactate exerts modulation of neuronal activity via a transmembranal receptor-linked mechanism. Here, we show that lactate causes biphasic modulation of the intrinsic excitability of CA1 pyramidal cells...
April 27, 2018: Hippocampus
Sergej Wuethrich, Deborah E Hannula, Fred W Mast, Katharina Henke
Our episodic memory stores what happened when and where in life. Episodic memory requires the rapid formation and flexible retrieval of where things are located in space. Consciousness of the encoding scene is considered crucial for episodic memory formation. Here, we question the necessity of consciousness and hypothesize that humans can form unconscious episodic memories. Participants were presented with subliminal scenes, that is, scenes invisible to the conscious mind. The scenes displayed objects at certain locations for participants to form unconscious object-in-space memories...
April 27, 2018: Hippocampus
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