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Ulises Rodríguez Domínguez, Jeremy B Caplan
Grid cells in rat medial entorhinal cortex are widely thought to play a major role in spatial behaviour. However, the exact computational role of the population of grid cells is not known. Here we provide a descriptive model, which nonetheless considers biologically feasible mechanisms, whereby the grid cells are viewed as a two-dimensional Fourier basis set, in hexagonal coordinates, with restricted availability of basis functions. With known properties imposed into the model parameters, we demonstrate how various empirical benchmark findings are straight-forward to understand in this model...
September 14, 2018: Hippocampus
L Nadel, A P Maurer
Many of the foundational theoretical ideas in the field of learning and memory are traced to Donald Hebb. Examination of these ideas and their evolution suggest that Karl Lashley might have significantly influenced their development. Here, we discuss the relationship between Hebb and Lashley, and the parallels between them. Many now investigating the neurobiological basis of memory may be unaware both of Hebb's original descriptions, and the likely substantial contributions of Lashley. Many of their concerns remain with us today, and by clarifying the history we hope to strengthen the foundations of our field...
September 14, 2018: Hippocampus
Long Xie, Sandhitsu R Das, Arun Pilania, Molly Daffner, Grace E Stockbower, Sudipto Dolui, Paul A Yushkevich, John A Detre, David A Wolk
Mild cognitive impairment (MCI) is considered a prodromal stage of Alzheimer's disease (AD), but is also recognized to be a heterogeneous condition. Biomarkers that predict AD progression in MCI are of clinical significance because they can be used better identify appropriate candidates for therapeutic intervention studies. It has been hypothesized that, comparing to structural measurements, functional ones maybe more sensitive to early disease abnormalities and the sensitivity could be further enhanced when combined with cognitive task, a "brain stress test"...
September 11, 2018: Hippocampus
Nicole M Long, Michael J Kahana
Our memories form a record not only of our experiences, but also of their temporal structure. Although memory for the temporal structure of experience likely relies on multiple neural systems, numerous studies have implicated the hippocampus in the encoding and retrieval of temporal information. The present review evaluates the literature on hippocampal contributions to human serial-order memory from the perspective of three cognitive theories: associative chaining theory, positional coding theory and retrieved-context theory...
September 4, 2018: Hippocampus
Geoffrey W Diehl, Olivia J Hon, Stefan Leutgeb, Jill K Leutgeb
Distinct functional cell types in the medial entorhinal cortex (mEC) have been shown to represent different aspects of experiences. To further characterize mEC cell populations, we examined whether spatial representations of neurons in mEC superficial layers depended on the scale of the environment and changed over extended time periods. Accordingly, mEC cells were recorded while rats repeatedly foraged in a small or a large environment in sessions that were separated by time intervals from minutes to hours...
September 2, 2018: Hippocampus
Jessica Robin, Yeshith Rai, Mikaeel Valli, Rosanna K Olsen
Theoretical accounts of medial temporal lobe (MTL) function ascribe different functions to subregions of the MTL including perirhinal, entorhinal, parahippocampal cortices and the hippocampus. Some have suggested that the functional roles of these subregions vary in terms of their category specificity, showing preferential coding for certain stimulus types, but the evidence for this functional organization is mixed. In this systematic review, we evaluate existing evidence for regional specialization in the MTL for three categories of visual stimuli: faces, objects and scenes...
August 28, 2018: Hippocampus
Min Whan Jung, Hyunjung Lee, Yeongseok Jeong, Jong Won Lee, Inah Lee
Despite tremendous progress, the neural circuit dynamics underlying hippocampal mnemonic processing remain poorly understood. We propose a new model for hippocampal function-the simulation-selection model-based on recent experimental findings and neuroecological considerations. Under this model, the mammalian hippocampus evolved to simulate and evaluate arbitrary navigation sequences. Specifically, we suggest that CA3 simulates unexperienced navigation sequences in addition to remembering experienced ones, and CA1 selects from among these CA3-generated sequences, reinforcing those that are likely to maximize reward during offline idling states...
August 28, 2018: Hippocampus
K Ulrich, M J Spriggs, W C Abraham, J C Dalrymple-Alford, N McNaughton
The anterior thalamic nuclei (ATN) are a major interface between the hippocampus and prefrontal cortex within an extended Papez circuit. Rat models suggest that the deficits caused by ATN damage, which is associated with 'diencephalic amnesia', can be ameliorated by environmental enrichment (EE) through unknown mechanisms. We examined whether changes in theta rhythmicity within and between the hippocampus and prefrontal cortex are influenced by EE in rats with ATN lesions. Here we show that ATN lesions and EE produced essentially opposed functional effects in terms of changes in rhythmicity between two consecutive trials when rats forage for chocolate hail...
August 28, 2018: Hippocampus
Jessica Winne, Rafael Franzon, Aron Miranda, Thawann Malfatti, João Patriota, Sanja Mikulovic, Katarina E Leão, Richardson N Leão
Salicylate intoxication is a cause of tinnitus in humans and it is often used to produce tinnitus-like perception in animal models. Here we assess whether salicylate induces anxiety-like electrophysiological and behavioural signs. Using microwire electrode arrays, we recorded local field potential in the ventral and, in some experiments dorsal hippocampus, in an open field arena 1 hour after salicylate (300mg/kg) injection. We found that animals treated with salicylate moved dramatically less than saline treated animals...
August 28, 2018: Hippocampus
Honi Sanders, Daoyun Ji, Takuya Sasaki, Jill K Leutgeb, Matthew A Wilson, John E Lisman
Hippocampal place cells represent non-spatial information in addition to their more frequently studied spatial response properties. This encoding of non-spatial information by a process called rate remapping involves the increase or decrease in the firing rate of a place cell without changes in its spatial specificity. However, many hippocampal phenomena occur on very short time scales over which long-term average firing rates are not an appropriate description of activity. To understand how rate remapping relates to fine-scale temporal firing phenomena in the hippocampus, we studied place cell responses during two tasks that induce rate remapping...
August 21, 2018: Hippocampus
Marlena Wosiski-Kuhn, Mihail Bota, Christina A Snider, Steven P Wilson, Kannan U Venkataraju, Pavel Osten, Alexis M Stranahan
Diabetes increases adrenal steroids in humans and animal models, but potential interactions with psychological stress remain poorly understood. Diabetic rodents exhibit anxiety and reductions in hippocampal brain-derived neurotrophic factor (BDNF) expression, and these studies investigated whether loss of BDNF-driven hippocampal activity promotes anxiety and disinhibits the HPA axis. Mice with genetic obesity and diabetes (db/db) received intrahippocampal injections of lentivirus for BDNF overexpression (db/db-BDNFOE), and Wt mice received lentiviral constructs for BDNF knockdown (Wt-BDNFKD)...
August 11, 2018: Hippocampus
Keith A Hawkins, Nazli Emadi, Godfrey D Pearlson, Beth Taylor, Sabin Khadka, Diana King, Karen Blank
From middle age the hippocampus atrophies at an accelerating rate. Factors that further this acceleration may hasten memory decline and the onset of memory disorder. We studied associations between smoking history, age, ApoE e4 genotype, vascular risk factors, hippocampal volume, and cognition in 67 middle-aged subjects (mean age = 56 years) who were offspring of parents with dementia. Subjects underwent isotropic T1-weighted 3 T MRI brain scanning with FreeSurfer volumetric data extraction for the hippocampus, a neuropsychological assessment battery, extensive medical data collection, and ApoE genotyping...
August 1, 2018: Hippocampus
Ralitsa Todorova, Michaël Zugaro
Hippocampal sharp wave-ripple complexes are transient events of highly synchronous neuronal activity that typically occur during 'offline' brain states. This endogenous surge of activity consists in behaviorally relevant spiking patterns, describing spatial trajectories. They have been shown to play a critical role in memory consolidation during sleep and in navigational planning during wake. Beyond their local impact within the hippocampal formation, ripples also exert direct and indirect effects on target cortical and subcortical areas, which are thought to play a key role in information processing and semantic network reconfiguration...
August 1, 2018: Hippocampus
Nahid Zokaei, Matthew M Nour, Annie Sillence, Daniel Drew, Jane Adcock, Richard Stacey, Natalie Voets, Arjune Sen, Masud Husain
Classical views of the medial temporal lobe (MTL) have established that it plays a crucial role in long-term memory (LTM) (e.g. Scoville and Milner, 1957). Here we demonstrate, in a sample of patients who have undergone anterior temporal lobectomy for the treatment of epilepsy, that the MTL additionally plays a specific, causal role in short-term memory (STM). Patients and healthy control participants performed a STM task with a sensitive continuous report measure. This paradigm allowed us to examine recall memory for object identity, location and object-location binding, independently on a trial-by-trial basis...
August 1, 2018: Hippocampus
Govert Hoogland, Ruben G F Hendriksen, Rutger J Slegers, Marc P H Hendriks, Olaf E M G Schijns, Marlien W Aalbers, Johan S H Vles
Dystrophin is an important protein within the central nervous system. The absence of dystrophin, characterizing Duchenne Muscular Dystrophy (DMD), is associated with brain related comorbidities such as neurodevelopmental (e.g. cognitive and behavioural) deficits and epilepsy. Especially mutations in the downstream part of the DMD gene affecting the dystrophin isoforms Dp140 and Dp71 are found to be associated with cognitive deficits. However, the function of Dp140 is currently not well understood and its expression pattern has previously been implicated to be developmentally regulated...
August 1, 2018: Hippocampus
Fei Gao, Xuntao Yin, Richard A E Edden, Alan C Evans, Junhai Xu, Guanmei Cao, Honghao Li, Muwei Li, Bin Zhao, Jian Wang, Guangbin Wang
There is growing evidence for dysfunctional glutamatergic excitation and/or gamma-aminobutyric acid (GABA)ergic inhibition in patients with multiple sclerosis (MS). Cognitive impairment may occur during the early stages of MS and hippocampal abnormalities have been suggested as biomarkers. However, researchers have not clearly determined whether changes in hippocampal GABA and glutamate (Glu) levels are associated with cognitive impairment and aberrant neural activity in patients with MS. We used magnetic resonance spectroscopy to measure GABA+ and Glu levels in the left hippocampal region of 29 patients with relapsing-remitting MS and 29 healthy controls (HCs)...
August 1, 2018: Hippocampus
Jogender Mehla, Scott H Deibel, Jamshid Faraji, Takashi Saito, Takaomi C Saido, Majid H Mohajerani, Robert J McDonald
Most studies investigating hippocampal dependent learning and memory in mouse models of disease use the standard version of the MWT, in which a place is learned over several days. While useful in determining if there are learning and memory deficits, often it is not clear if memory acquisition, consolidation, or retrieval is affected. For rats, we developed a variant of the task in which we added a single massed training session to a new location after the standard distributed version of the MWT. Using this version of the task, competition between these two spatial representations can then be assessed in a probe trial...
August 1, 2018: Hippocampus
Benjamin M Basile, Robert R Hampton
Evidence that the hippocampus is critical for spatial memory in nonnavigational tests is mixed. A recent study reported that temporary hippocampal inactivation impaired spatial memory in the nonnavigational Hamilton Search Task in monkeys. However, several studies have documented no impairment on other nonnavigational spatial memory tests following permanent hippocampal lesions. It was hypothesized that transient, but not permanent, hippocampal disruption produces deficits because monkeys undergoing transient inactivation continue to try to use a hippocampal-dependent strategy, whereas monkeys with permanent lesions use a nonhippocampal-dependent strategy...
August 1, 2018: Hippocampus
Thomas D Helton, Meilan Zhao, Shannon Farris, Serena M Dudek
Excitatory synaptic inputs from specific brain regions are often targeted to distinct dendritic arbors on hippocampal pyramidal neurons. Recent work has suggested that CA2 pyramidal neurons respond robustly and preferentially to excitatory input into the stratum lacunosum moleculare (SLM), with a relatively modest response to Schaffer collateral excitatory input into stratum radiatum (SR) in acute mouse hippocampal slices, but the extent to which this difference may be explained by morphology is unknown. In an effort to replicate these findings and to better understand the role of dendritic morphology in shaping responses from proximal and distal synaptic sites, we measured excitatory postsynaptic currents and action potentials in CA2 pyramidal cells in response to SR and SLM stimulation and subsequently analyzed confocal images of the filled cells...
August 1, 2018: Hippocampus
Alessandra Mallei, Alessandro Ieraci, Stefano Corna, Daniela Tardito, Francis S Lee, Maurizio Popoli
Brain derived neurotrophic factor (BDNF), a neurotrophin highly expressed in the hippocampus, plays crucial roles in cognition, neuroplasticity, synaptic function and dendritic remodeling. The common human Val66Met polymorphism of BDNF has been implicated in the pathophysiology of neuropsychiatric and neurodegenerative disorders, and in the outcome of pro-adaptive and therapeutic treatments. Altered gene expression profile has been previously shown in BDNF Val66Met knock-in mice, which recapitulate the phenotypic hallmarks of individuals carrying the BDNF Met allele...
August 1, 2018: Hippocampus
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