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Boris Mlinar, Renato Corradetti
The hippocampus is functionally differentiated along its longitudinal axis, with the dorsal and ventral segments preferentially involved in cognitive and emotional processing, respectively. Serotonergic modulation of hippocampal function has been extensively studied, but its relation to the dorsoventral axis has remained largely unknown. To examine the modulation of hippocampal output along the dorsoventral axis by endogenous serotonin (5-HT) we compared the effect of the 5-HT/noradrenaline (NA)-releaser, 3,4-methylenedioxymethamphetamine (MDMA), in transversal slices encompassing the entire rat hippocampus...
December 20, 2017: Hippocampus
Brad E Pfeiffer
One of the most striking features of the hippocampal network is its ability to self-generate neuronal sequences representing temporally compressed, spatially coherent paths. These brief events, often termed "replay" in the scientific literature, are largely confined to non-exploratory states such as sleep or quiet rest. Early studies examining the content of replay noted a strong correlation between the encoded spatial information and the animal's prior behavior; thus, replay was initially hypothesized to play a role in memory formation and/or systems-level consolidation via "off-line" reactivation of previous experiences...
December 20, 2017: Hippocampus
Charlis Raineki, Linda Ellis, Joanne Weinberg
Many functions of the hippocampus are affected by prenatal alcohol exposure (PAE). In particular, dysregulation of the stress response is especially important because individuals with PAE carry increased risks for exposure to stressful environments throughout life. Little is known, though, about how adolescent stress in the context of PAE-related stress system dysregulation may further alter hippocampal development. Here we investigate the short- and long-term effects of adolescent chronic mild stress (CMS) on mRNA expression of stress-related mineralocorticoid (MR), glucocorticoid (GR), and type 1 CRH (CRHR1) receptors in the dorsal and ventral hippocampal formation of PAE and control rats...
December 18, 2017: Hippocampus
Joel E Soler, Alfred J Robison, Antonio A Núñez, Lily Yan
The effects of light on cognitive function have been well-documented in human studies, with brighter illumination improving cognitive performance in school children, healthy adults and patients in early stages of dementia. However, the underlying neural mechanisms are not well understood. The present study examined how ambient light affects hippocampal function using the diurnal Nile grass rats (Arvicanthis niloticus) as the animal model. Grass rats were housed in either a 12:12hr bright light-dark (brLD, 1000 lux) or dim light-dark (dimLD, 50 lux) cycle...
December 18, 2017: Hippocampus
Mark C Zielinski, Wenbo Tang, Shantanu P Jadhav
Sequential activity is seen in the hippocampus during multiple network patterns, prominently as replay activity during both awake and sleep sharp-wave ripples (SWRs), and as theta sequences during active exploration. Although various mnemonic and cognitive functions have been ascribed to these hippocampal sequences, evidence for these proposed functions remains primarily phenomenological. Here, we briefly review current knowledge about replay events and theta sequences in spatial memory tasks. We reason that in order to gain a mechanistic and causal understanding of how these patterns influence memory and cognitive processing, it is important to consider how these sequences influence activity in other regions, and in particular, the prefrontal cortex, which is crucial for memory-guided behavior...
December 18, 2017: Hippocampus
Kevin M Horecka, Michael Dulas, Hillary Schwarb, Heather Lucas, Melissa Duff, Neal J Cohen
Hippocampal involvement in learning and remembering relational information has an extensive history, often focusing specifically on spatial information. In humans, spatial reconstruction (SR) paradigms are a powerful tool for evaluating an individuals' spatial-relational memory. In SR tasks, participants study locations of items in space and subsequently reconstruct the studied display after a short delay. Previous work has revealed that patients with hippocampal damage are impaired both in overall placement accuracy as well as on a specific measure of relational memory efficacy, "swaps" (i...
December 12, 2017: Hippocampus
M K Chawla, V L Sutherland, K Olson, B L McNaughton, C A Barnes
Anatomical connectivity and lesion studies reveal distinct functional heterogeneity along the dorsal-ventral axis of the hippocampus. The immediate early gene Arc is known to be involved in neural plasticity and memory and can be used as a marker for cell activity that occurs, for example, when hippocampal place cells fire. We report here, that Arc is expressed in a greater proportion of cells in dorsal CA1, CA3 and dentate gyrus (DG), following spatial behavioral experiences compared to ventral hippocampal subregions (dorsal CA1= 33%; ventral CA1= 13%; dorsal CA3 = 23%; ventral CA3 = 8%; and dorsal DG = 2...
December 12, 2017: Hippocampus
Daniela J Palombo, Agnes Bacopulos, Robert S C Amaral, Rosanna K Olsen, Rebecca M Todd, Adam K Anderson, Brian Levine
Striking individual differences exist in the human capacity to recollect past events, yet, little is known about the neural correlates of such individual differences. Studies investigating hippocampal volume in relation to individual differences in laboratory measures of episodic memory in young adults suggest that whole hippocampal volume is unrelated (or even negatively associated) with episodic memory. However, anatomical and functional specialization across hippocampal subregions suggests that individual differences in episodic memory may be linked to particular hippocampal subregions, as opposed to whole hippocampal volume...
November 24, 2017: Hippocampus
Valentyna Dubovyk, Denise Manahan-Vaughan
The dorsoventral axis of the hippocampus exhibits functional differentiations with regard to (spatial Vs emotional learning) and information retention (rapid encoding Vs long-term storage), as well as its sensitivity to neuromodulation and information received from extrahippocampal structures. The mechanisms that underlie these differentiations remain unclear. Here, we explored neurotransmitter receptor expression along the dorsoventral hippocampal axis and compared hippocampal synaptic plasticity in the CA1 region of the dorsal (DH), intermediate (IH) and ventral hippocampi (VH)...
November 24, 2017: Hippocampus
Kristin Nordin, Jonas Persson, Eva Stening, Agneta Herlitz, Elna-Marie Larsson, Hedvig Söderlund
The hippocampus interacts with distributed brain regions to support memory and shows significant volume reductions in aging, but little is known about age effects on hippocampal whole-brain structural covariance. It is also unclear whether the anterior and posterior hippocampus show similar or distinct patterns of whole-brain covariance and to what extent these are related to memory functions organized along the hippocampal longitudinal axis. Using the multivariate approach partial least squares (PLS), we assessed structural whole-brain covariance of the hippocampus in addition to regional volume, in young, middle-aged and older adults (n=221), and assessed associations with episodic and spatial memory...
November 24, 2017: Hippocampus
Brook A L Perry, Stephanie A Mercer, Sophie C Barnett, Jungah Lee, John C Dalrymple-Alford
The anterior thalamic nuclei (ATN), mammillary bodies and their interconnecting fiber tract, the mammillothalamic tract (MTT), are important components of an extended hippocampal circuit for episodic memory. In humans, damage to the MTT or ATN in many disorders is associated with severe anterograde amnesia and it is assumed that their influence on memory is functionally equivalent. The relative influence of these two structures on memory has not, however, been assessed explicitly. Here, a direct comparison found that only ATN lesions impaired spatial reference memory in rats...
November 18, 2017: Hippocampus
Hugo J Spiers, H Freyja Olafsdottir, Colin Lever
Coding the distance to a future goal is an important function of a neural system supporting navigation. While some evidence indicates the hippocampus increases activity with proximity to the goal, others have found activity to decreases with proximity. To explore goal distance coding in the hippocampus we recorded from CA1 hippocampal place cells in rats as they navigated to learned goals in an event arena with a win-stay lose-shift rule. CA1 activity was positively correlated with the distance - decreasing with proximity to the goal...
November 17, 2017: Hippocampus
Christopher R Doxey, Cooper B Hodges, Ty A Bodily, Nathan M Muncy, C Brock Kirwan
Effective memory representations must be specific to prevent interference between episodes that may overlap in terms of place, time, or items present. Pattern separation, a computational process performed by the hippocampus, overcomes this interference by establishing nonoverlapping memory representations. Although it is widely accepted that declarative memories are consolidated during sleep, the effects of sleep on pattern separation have yet to be elucidated. We used whole-brain, high-resolution functional neuroimaging to investigate the effects of sleep on a task that places high demands on pattern separation...
November 17, 2017: Hippocampus
Karen L Campbell, Kevin P Madore, Roland G Benoit, Preston P Thakral, Daniel L Schacter
Both the hippocampus and ventromedial prefrontal cortex (vmPFC) appear to be critical for episodic future simulation. Damage to either structure affects one's ability to remember the past and imagine the future, and both structures are commonly activated as part of a wider core network during future simulation. However, the precise role played by each of these structures and, indeed, the direction of information flow between them during episodic simulation, is still not well understood. In this study, we scanned participants using functional magnetic resonance imaging while they imagined future events in response to object cues...
November 8, 2017: Hippocampus
Bianca Völkening, Kai Schönig, Golo Kronenberg, Dusan Bartsch, Tillmann Weber
In the central nervous system, CaV 1.2 and CaV 1. 3 constitute the main L-type voltage-gated calcium channels (LTCCs) coupling membrane depolarization to gene transcription. We have previously demonstrated that inducible disruption of Cav1.2 in type-1 astrocyte-like stem cells of the adult dentate gyrus (DG) impairs hippocampal neurogenesis in a cell-autonomous fashion. To address the role of Cav1.3 channels (encoded by the Cacna1d gene), we here generated Tg(GLAST-CreERT2) /Cacna1d(fl/fl) /RCE:loxP mice which facilitate inducible deletion of Cacna1d in tandem with induction of EGFP expression in type-1 cells, allowing tracking of recombined cells and their descendants...
November 8, 2017: Hippocampus
H Tanila, S Ku, F Kloosterman, M A Wilson
For the sake of rigorous control of task variables, hippocampal place cells have been usually studied in relatively simple environments. To approach the situation of real-life navigation in an urban-like environment, we recorded CA1 place cells while rats performance a memory task in a 'Townmaze' with two start locations, three alternate paths in the maze mid-section, followed by a two-way choice that determined the trial outcome, access to a goal compartment. Further, to test the ability of place cells to update their spatial representation upon local changes in the environment while maintaining the integrity of the overall spatial map to allow effective navigation, we occasionally introduced barriers in the maze mid-section to force the rat to select a nonpreferred route...
October 26, 2017: Hippocampus
Colin T Kyle, Jared Stokes, Jeffrey Bennett, Jeri Meltzer, Michele R Permenter, Julie A Vogt, Arne Ekstrom, Carol A Barnes
Identification of primate hippocampal subfields in vivo using structural MRI imaging relies on variable anatomical guidelines, signal intensity differences, and heuristics to differentiate between regions (Yushkevich et al., ). Thus, a clear anatomically-driven basis for subfield demarcation is lacking. Recent work, however, has begun to develop methods to use ex vivo histology or ex vivo MRI (Adler et al., 2014; Iglesias et al., 2015) that have the potential to inform subfield demarcations of in vivo images...
October 26, 2017: Hippocampus
Anna Pajkert, Carsten Finke, Yee Lee Shing, Martina Hoffmann, Werner Sommer, Hauke R Heekeren, Christoph J Ploner
Adaptive behavior frequently depends on inference from past experience. Recent studies suggest that the underlying process of integrating related memories may depend on interaction between hippocampus and prefrontal cortex. Here, we investigated how hippocampal damage affects memory integration. Subjects with mediotemporal lesions and healthy controls learned a set of overlapping AB- and BC-associations (object-face- and face-object pairs) and were then tested for memory of these associations ("direct" trials) and of inferential AC-associations ("indirect" trials)...
December 2017: Hippocampus
Eugenio Urdapilleta, Bailu Si, Alessandro Treves
A unique topographical representation of space is found in the concerted activity of grid cells in the rodent medial entorhinal cortex. Many among the principal cells in this region exhibit a hexagonal firing pattern, in which each cell expresses its own set of place fields (spatial phases) at the vertices of a triangular grid, the spacing and orientation of which are typically shared with neighboring cells. Grid spacing, in particular, has been found to increase along the dorso-ventral axis of the entorhinal cortex but in discrete steps, that is, with a modular structure...
November 2017: Hippocampus
Mathilde Bostelmann, Emilie Fragnière, Floriana Costanzo, Silvia Di Vara, Deny Menghini, Stefano Vicari, Pierre Lavenex, Pamela Banta Lavenex
Williams syndrome (WS), a genetic deletion syndrome, is characterized by severe visuospatial deficits affecting performance on both tabletop spatial tasks and on tasks which assess orientation and navigation. Nevertheless, previous studies of WS spatial capacities have ignored the fact that two different spatial memory systems are believed to contribute parallel spatial representations supporting navigation. The place learning system depends on the hippocampal formation and creates flexible relational representations of the environment, also known as cognitive maps...
November 2017: Hippocampus
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