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Hippocampus and retrieval

Vera Flasbeck, Erika Atucha, Nozomu H Nakamura, Motoharu Yoshida, Magdalena M Sauvage
For the past decades, CA3 was considered as a single functional entity. However, strong differences between the proximal (close to the dentate gyrus) and the distal (close to CA2) parts of CA3 in terms of connectivity patterns, gene expression and electrophysiological properties suggest that it is not the case. We recently showed that proximal CA3 (together with distal CA1) preferentially deals with non-spatial information [1]. In contrast to proximal CA3, distal CA3 mainly receives and predominantly projects to spatially tuned areas...
August 8, 2018: Behavioural Brain Research
Oressia Zalucki, Danyon Harkins, Lachlan Harris, Thomas H J Burne, Richard M Gronostajski, Michael Piper
OBJECTIVE: The active place avoidance task (APA) is a behavioural task used to assess learning and memory in rodents. This task relies on the hippocampus, a region of the cerebral cortex capable of generating new neurons from neural stem cells. In this study, to gain further insight into the behavioural phenotype of mice deficient in the transcription factor Nfix, a gene expressed by adult neural stem cells, we examined learning and memory parameters from the APA task that were not published in our original investigation...
August 6, 2018: BMC Research Notes
Jena B Hales, Jonathan L Vincze, Nicole T Reitz, Amber C Ocampo, Stefan Leutgeb, Robert E Clark
The hippocampus is critically involved in the acquisition and retrieval of spatial memories. Even though some memories become independent of the hippocampus over time, expression of spatial memories have consistently been found to permanently depend on the hippocampus. Recent studies have focused on the adjacent medial entorhinal cortex (MEC), as it provides major projections to the hippocampus. These studies have shown that lesions of the MEC disrupt spatial processing in the hippocampus and impair spatial memory acquisition on the watermaze task...
July 31, 2018: Neurobiology of Learning and Memory
Chen-Cheng Lin, Kun-Lun Huang, Che-Se Tung, Yia-Ping Liu
Individuals with posttraumatic stress disorder (PTSD) are characterized by fear memory problems and hypocortisolemia of which traumatic stress-induced monoaminergic disruption over infralimbic (IL) cortex is considered the key mechanism. Hyperbaric oxygen therapy (HBOT) has recently proven its utility in treating several mental disorders but remains unexplored for PTSD. The present study aimed to examine the effects of 5-day HBO paradigm on traumatic stress (single prolonged stress, SPS, an animal model of PTSD)-induced dysregulation of fear memory/anxiety profiles and related abnormalities in IL monoamines and plasma corticosterone...
July 26, 2018: Behavioural Brain Research
Nicola Solari, Balázs Hangya
Spatial learning, including encoding and retrieval of spatial memories as well as holding spatial information in working memory generally serving navigation under a broad range of circumstances, relies on a network of structures. While central to this network are medial temporal lobe structures with a widely appreciated crucial function of the hippocampus, neocortical areas such as the posterior parietal cortex and the retrosplenial cortex also play essential roles. Since the hippocampus receives its main subcortical input from the medial septum of the basal forebrain cholinergic system, it is not surprising that the potential role of the septo-hippocampal pathway in spatial navigation has been investigated in many studies...
July 28, 2018: European Journal of Neuroscience
Lexia Zhan, Dingrong Guo, Gang Chen, Jiongjiong Yang
When stimuli are learned by repetition, they are remembered better and retained for a longer time. However, current findings are lacking as to whether the medial temporal lobe (MTL) and cortical regions are involved in the learning effect when subjects retrieve associative memory, and whether their activations differentially change over time due to learning experience. To address these issues, we designed an fMRI experiment in which face-scene pairs were learned once (L1) or six times (L6). Subjects learned the pairs at four retention intervals, 30-min, 1-day, 1-week and 1-month, after which they finished an associative recognition task in the scanner...
2018: Frontiers in Human Neuroscience
Sean Froudist-Walsh, Philip G F Browning, Paula L Croxson, Kathy L Murphy, Jul Lea Shamy, Tess L Veuthey, Charles R E Wilson, Mark G Baxter
Humans can recall a large number of memories years after the initial events. Patients with amnesia often have lesions to the hippocampus, but human lesions are imprecise, making it difficult to identify the anatomy underlying memory impairments. Rodent studies enable great precision in hippocampal manipulations, but not investigation of many interleaved memories. Thus it is not known how lesions restricted to the hippocampus affect the retrieval of multiple sequentially encoded memories. Furthermore, disagreement exists as to whether hippocampal inactivations lead to temporally graded or ungraded amnesia, which could be a consequence of differences between rodent and human studies...
July 26, 2018: Journal of Neuroscience: the Official Journal of the Society for Neuroscience
Timothy J Jarome, Gabriella A Perez, Rebecca M Hauser, Katrina M Hatch, Farah D Lubin
Memory retrieval induces a transient period of increased transcriptional and translational regulation in neurons called reconsolidation, which is regulated by the Protein Kinase B - mammalian target of rapamycin (AKT-mTOR) pathway. However, it is currently unknown how activation of the AKT-mTOR pathway is regulated during the reconsolidation process. Here, we found that in male rats retrieval of a contextual fear memory transiently increased EZH2 levels along with increased histone H3 lysine 27 trimethylation (H3K27me3) levels, which correlated with decreased levels of PTEN, a potent inhibitor of AKT-mTOR-dependent signaling in the hippocampus...
July 20, 2018: Journal of Neuroscience: the Official Journal of the Society for Neuroscience
Gerrit Höltje, Axel Mecklinger
Previous research has shown that in reinforcement learning, the hippocampus is involved in the processing of feedback when it is delayed for several seconds. Also, better recognition memory has been reported for temporally delayed than for immediately presented feedback pictures. Event-related potential (ERP) studies have found that feedback delay affects the amplitude of the feedback-related negativity (FRN), and there is evidence suggesting that the FRN is modulated by declarative learning. In the present study, a subsequent memory paradigm was used to investigate the effects of feedback delay on the incidental encoding and subsequent retrieval of feedback events...
July 12, 2018: Brain Research
Justine E Cohen, Robert S Ross, Chantal E Stern
Previous research has demonstrated that areas in the medial temporal lobe and prefrontal cortex (PFC) show increased activation during retrieval of overlapping sequences. In this study, we designed a task in which degree of overlap varied between conditions in order to parse out the contributions of hippocampal and prefrontal subregions as overlap between associations increased. In the task, participants learned sequential associations consisting of a picture frame, a face within the picture frame, and an outdoor scene...
August 2018: Learning & Memory
Youssef Ezzyat, Marika Inhoff, Lila Davachi
It is well known that distributing study events over time leads to better memory over long timescales, compared to massing study events together. One explanation for such long-term resistance to forgetting is that distributed study leads to neural differentiation in memory, which supports retrieval of past experiences by disambiguating highly similar memory representations. Neuroanatomical models of episodic memory retrieval propose that the hippocampus and medial prefrontal cortex (MPFC) work together to enable retrieval of behaviorally appropriate memories...
July 16, 2018: Journal of Neuroscience: the Official Journal of the Society for Neuroscience
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
Lynn J Lohnas, Katherine Duncan, Werner K Doyle, Thomas Thesen, Orrin Devinsky, Lila Davachi
Mnemonic decision-making has long been hypothesized to rely on hippocampal dynamics that bias memory processing toward the formation of new memories or the retrieval of old ones. Successful memory encoding may be best optimized by pattern separation, whereby two highly similar experiences can be represented by underlying neural populations in an orthogonal manner. By contrast, successful memory retrieval is thought to be supported by a recovery of the same neural pattern laid down during encoding. Here we examined how hippocampal pattern completion and separation emerge over time during memory decisions...
July 31, 2018: Proceedings of the National Academy of Sciences of the United States of America
Alan King Lun Liu, Ernest Junwei Lim, Idil Ahmed, Raymond Chuen-Chung Chang, Ronald K B Pearce, Steve M Gentleman
Although the nucleus of the vertical limb of the diagonal band of Broca (nvlDBB) is the second largest cholinergic nucleus in the basal forebrain, after the nucleus basalis of Meynert (nbM), it has not generally been a focus for studies of neurodegenerative disorders. However, the nvlDBB does have an important projection to the hippocampus and discrete lesions of the rostral basal forebrain have been shown to disrupt retrieval memory function, a major deficit seen in patients with Lewy body disorders. One reason for its neglect is that the anatomical boundaries of the nvlDBB are ill defined and this area of the brain is not part of routine diagnostic sampling protocols...
July 13, 2018: Neuropathology and Applied Neurobiology
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
Jennifer T Sneider, Julia E Cohen-Gilbert, Derek A Hamilton, Elena R Stein, Noa Golan, Emily N Oot, Anna M Seraikas, Michael L Rohan, Sion K Harris, Lisa D Nickerson, Marisa M Silveri
The frontal cortex undergoes substantial structural and functional changes during adolescence and significant developmental changes also occur in the hippocampus. Both of these regions are notably vulnerable to alcohol and other substance use, which is typically initiated during adolescence. Identifying measures of brain function during adolescence, particularly before initiation of drug or alcohol use, is critical to understanding how such behaviors may affect brain development, especially in these vulnerable brain regions...
2018: Frontiers in Human Neuroscience
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
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
Peter Kok, Nicholas B Turk-Browne
Perception can be cast as a process of inference, in which bottom-up signals are combined with top-down predictions in sensory systems. In line with this, neural activity in sensory cortex is strongly modulated by prior expectations. Such top-down predictions often arise from cross-modal associations, such as when a sound (e.g., bell or bark) leads to an expectation of the visual appearance of the corresponding object (e.g., bicycle or dog). We hypothesised that the hippocampus - which rapidly learns arbitrary relations between stimuli over space and time - may be involved in forming such associative predictions...
July 9, 2018: Journal of Neuroscience: the Official Journal of the Society for Neuroscience
Axel Guskjolen, Justin W Kenney, Juan de la Parra, Bi-Ru Amy Yeung, Sheena A Josselyn, Paul W Frankland
Hippocampus-dependent, event-related memories formed in early infancy in human and non-human animals are rapidly forgotten. Recently we found that high levels of hippocampal neurogenesis contribute to accelerated rates of forgetting during infancy. Here, we ask whether these memories formed in infancy are permanently erased (i.e., storage failure) or become progressively inaccessible with time (i.e., retrieval failure). To do this, we developed an optogenetic strategy that allowed us to permanently express channelrhodopsin-2 (ChR2) in neuronal ensembles that were activated during contextual fear encoding in infant mice...
July 23, 2018: Current Biology: CB
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