scholarly journals Dynamic representation of space in the hippocampus: spatial novelty detection and consolidation in CA1 and CA2

2021 ◽  
Author(s):  
Guncha Bhasin
Keyword(s):  
Novelty Detection ◽  
Place Cells ◽  
Neuronal Responses ◽  
Dynamic Representation ◽  
Spatial Novelty ◽  
Spatial Coverage ◽  
Representation Of Space ◽  
Familiar Environment ◽  
First Time ◽  
Processing Differences

Hippocampal place cells are the functional units of spatial navigation and are present in all subregions- CA1, CA2, CA3 and CA4. Recent studies on CA2 have indicated its role in social and contextual memory, but its contribution towards spatial novelty detection and consolidation remains largely unknown. The current study aims to uncover how CA1 and CA2 detect, process, assimilate and consolidate spatial novelty. Accordingly, a novel 3-day paradigm was designed where the animal was introduced to a completely new environment on the first day and to varying degrees of familiarity and novelty on subsequent days, as the track was extended in length and modified in shape, keeping other environmental constraints fixed. Detection of spatial novelty was found to be a dynamic and complex phenomenon, characterized by different responses from hippocampal place cells, depending on when novelty was introduced. Therefore, the study concludes that early novelty detection (the first time a novel space is introduced in a relatively familiar environment) and subsequent novelty detection are not processed in the same way. Additionally, while neuronal responses to spatial novelty detection (early and subsequent) were found to be the same in CA1 and CA2 ensembles, their responses differed in spatial consolidation mechanisms during subsequent sleep replays. For CA1, spatial coverage of prior behaviour was found to be closely reflected in subsequent sleep for that particular day, but CA2 showed no such coherent response, highlighting mnemonic processing differences between CA2 and CA1 with respect to spatial novelty.

scholarly journals Place Cells in the Claustrum Remap Under NMDA Receptor Control

2021 ◽  
Author(s):  
Emanuela Rizello ◽  
Sean Martin ◽  
Jennifer Rouine ◽  
Charlotte Callaghan ◽  
Shane O'Mara
Keyword(s):  
Nmda Receptor ◽  
Place Cells ◽  
Receptor Activity ◽  
Oscillatory Activity ◽  
Neuronal Responses ◽  
Place Field ◽  
Visual Inputs ◽  
Delta Band ◽  
Cortical Inputs ◽  
Visual Cortical

Place cells are cells exhibiting location-dependent responses; they have mostly been studied in the hippocampus. Place cells have also been reported in the rat claustrum, an underexplored paracortical region with extensive corto-cortical connectivity. It has been hypothesised that claustral neuronal responses are anchored to cortical visual inputs. We show rat claustral place cells remap when visual inputs are eliminated from the environment and that this remapping is NMDA-receptor-dependent. Eliminating visual input enhances delta-band oscillatory activity in the claustrum, without affecting simultaneously-recorded visual cortical activity. We conclude that, like the hippocampus, claustral place field remapping might be mediated by NMDA receptor activity, and is modulated by visual cortical inputs.

scholarly journals A bulk-mass-modeling-based method for retrieving particulate matter pollution using CALIOP observations

2019 ◽  
Vol 12 (3) ◽  
pp. 1739-1754 ◽  
Author(s):  
Travis D. Toth ◽  
Jianglong Zhang ◽  
Jeffrey S. Reid ◽  
Mark A. Vaughan
Keyword(s):  
Particulate Matter ◽  
Orthogonal Polarization ◽  
Empirical Relationships ◽  
Near Surface ◽  
Bulk Mass ◽  
Spatial Coverage ◽  
Sensitivity Studies ◽  
First Time ◽  
Good Agreement ◽  
Particulate Matter Pollution

Abstract. In this proof-of-concept paper, we apply a bulk-mass-modeling method using observations from the NASA Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument for retrieving particulate matter (PM) concentration over the contiguous United States (CONUS) over a 2-year period (2008–2009). Different from previous approaches that rely on empirical relationships between aerosol optical depth (AOD) and PM2.5 (PM with particle diameters less than 2.5 µm), for the first time, we derive PM2.5 concentrations, during both daytime and nighttime, from near-surface CALIOP aerosol extinction retrievals using bulk mass extinction coefficients and model-based hygroscopicity. Preliminary results from this 2-year study conducted over the CONUS show a good agreement (r2∼0.48; mean bias of −3.3 µg m−3) between the averaged nighttime CALIOP-derived PM2.5 and ground-based PM2.5 (with a lower r2 of ∼0.21 for daytime; mean bias of −0.4 µg m−3), suggesting that PM concentrations can be obtained from active-based spaceborne observations with reasonable accuracy. Results from sensitivity studies suggest that accurate aerosol typing is needed for applying CALIOP measurements for PM2.5 studies. Lastly, the e-folding correlation length for surface PM2.5 is found to be around 600 km for the entire CONUS (∼300 km for western CONUS and ∼700 km for eastern CONUS), indicating that CALIOP observations, although sparse in spatial coverage, may still be applicable for PM2.5 studies.

Effects of exploring a novel environment on memory across the lifespan

2021 ◽  
Author(s):  
Judith Schomaker ◽  
Valentin Baumann ◽  
Marit Ruitenberg
Keyword(s):  
Older Adults ◽  
Declarative Memory ◽  
Word Recall ◽  
Younger Adults ◽  
Novel Environment ◽  
Beneficial Effects ◽  
Spatial Novelty ◽  
Familiar Environment ◽  
Shallow Condition ◽  
The Brain

Exploration is a crucial aspect of mammalian behavior, and new environments provide unique opportunities to learn. Exploration of a novel environment has been shown to promote memory formation in healthy adults, even for unrelated events. Studies in animals have suggested that such novelty-induced memory boosts are mediated by hippocampal dopamine. The dopaminergic system is known to develop and deteriorate over the lifespan, but so far, the effects of novelty on memory across the lifespan have not yet been investigated. In the current study, we used novel and previously familiarized virtual environments to pinpoint the effects of spatial novelty on declarative memory in humans across the lifespan. After exploring a novel or familiar environment, participants were presented a list of words, and either performed a semantic task (deep encoding) or judged whether the first letter of the shown word was open or closed (shallow encoding). Incidental memory was quantified in a surprise test. Our sample (n = 439) included children, adolescents, younger adults, and older adults. Results showed that participants in the deep encoding condition remembered more words than those in the shallow condition, but novelty did not influence this effect. Interestingly, however, children, adolescents and younger adults benefitted from exploring a novel compared to a familiar environment as evidenced by better word recall, while these effects were absent in older adults. Our findings suggest that the beneficial effects of novelty on memory follow the deterioration of pathways in the brain involved in novelty-related processing across the lifespan.

scholarly journals Representation of Objects in Space by Two Classes of Hippocampal Pyramidal Cells

2004 ◽  
Vol 124 (1) ◽  
pp. 9-25 ◽  
Author(s):  
Bruno Rivard ◽  
Yu Li ◽  
Pierre-Pascal Lenck-Santini ◽  
Bruno Poucet ◽  
Robert U. Muller
Keyword(s):  
Cell Activity ◽  
Pyramidal Cells ◽  
Place Cell ◽  
Place Cells ◽  
Rat Hippocampus ◽  
Ca1 Pyramidal Cells ◽  
New Class ◽  
Familiar Environment ◽  
Current Arrangement ◽  
Number Of Cells

Humans can recognize and navigate in a room when its contents have been rearranged. Rats also adapt rapidly to movements of objects in a familiar environment. We therefore set out to investigate the neural machinery that underlies this capacity by further investigating the place cell–based map of the surroundings found in the rat hippocampus. We recorded from single CA1 pyramidal cells as rats foraged for food in a cylindrical arena (the room) containing a tall barrier (the furniture). Our main finding is a new class of cells that signal proximity to the barrier. If the barrier is fixed in position, these cells appear to be ordinary place cells. When, however, the barrier is moved, their activity moves equally and thereby conveys information about the barrier's position relative to the arena. When the barrier is removed, such cells stop firing, further suggesting they represent the barrier. Finally, if the barrier is put into a different arena where place cell activity is changed beyond recognition (“remapping”), these cells continue to discharge at the barrier. We also saw, in addition to barrier cells and place cells, a small number of cells whose activity seemed to require the barrier to be in a specific place in the environment. We conclude that barrier cells represent the location of the barrier in an environment-specific, place cell framework. The combined place + barrier cell activity thus mimics the current arrangement of the environment in an unexpectedly realistic fashion.

scholarly journals Dynamic representation of 3D auditory space in the midbrain of the free-flying echolocating bat

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Ninad B Kothari ◽  
Melville J Wohlgemuth ◽  
Cynthia F Moss
Keyword(s):  
Physical Environment ◽  
Auditory Space ◽  
Neural Recordings ◽  
Dynamic Representation ◽  
3D Space ◽  
Sensory Mapping ◽  
Freely Moving ◽  
And Shifts ◽  
Space Coding ◽  
First Time

Essential to spatial orientation in the natural environment is a dynamic representation of direction and distance to objects. Despite the importance of 3D spatial localization to parse objects in the environment and to guide movement, most neurophysiological investigations of sensory mapping have been limited to studies of restrained subjects, tested with 2D, artificial stimuli. Here, we show for the first time that sensory neurons in the midbrain superior colliculus (SC) of the free-flying echolocating bat encode 3D egocentric space, and that the bat’s inspection of objects in the physical environment sharpens tuning of single neurons, and shifts peak responses to represent closer distances. These findings emerged from wireless neural recordings in free-flying bats, in combination with an echo model that computes the animal’s instantaneous stimulus space. Our research reveals dynamic 3D space coding in a freely moving mammal engaged in a real-world navigation task.

scholarly journals Inhibition of Protein Kinase M  Disrupts the Stable Spatial Discharge of Hippocampal Place Cells in a Familiar Environment

2012 ◽  
Vol 32 (40) ◽  
pp. 13753-13762 ◽  
Author(s):  
J. M. Barry ◽  
B. Rivard ◽  
S. E. Fox ◽  
A. A. Fenton ◽  
T. C. Sacktor ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Place Cells ◽  
Familiar Environment

scholarly journals Bundle-specific fornix reconstruction for dual-tracer PET-tractometry

2018 ◽  
Author(s):  
Francois Rheault ◽  
Maggie Roy ◽  
Stephen Cunnane ◽  
Maxime Descoteaux
Keyword(s):  
State Of The Art ◽  
Emission Tomography ◽  
Hippocampal Atrophy ◽  
Current State ◽  
Positron Emission ◽  
Spatial Coverage ◽  
Before And After ◽  
Position And Orientation ◽  
First Time ◽  
Dual Tracer

AbstractTractography is known to have problems reconstructing white matter bundles that are narrow, have high curvature, or go through partial volume voxels contaminated by CSF or gray matter. One such bundle is the fornix, the major output tract of the hippocampus, which is especially problematic with aging. Hippocampal atrophy and ventricular expansion make the fornix even harder (often impossible) to track with current state-of-the-art techniques. In this work, a bundle-specific tractography algorithm is proposed to fully reconstruct the fornix. By injecting shape, position, and orientation priors, fornix reconstruction is markedly is improved. We report an increase in spatial coverage and better reproducibility across test-retest. These improvements over classical tractography algorithms also enable tractometry of the fornix to be combined with dual-tracer positron emission tomography (PET) data in participants with mild cognitive impairment (MCI). MCI participants underwent a multi-modal brain imaging before and after a 6-month daily ketogenic supplement. We report, for the first time, significant diffusion measures and 18F-fluorodeoxyglucose (FDG) uptake differences in specific sub-sections of the fornix after the ketogenic supplement.

scholarly journals Recurrent network model for learning goal-directed sequences through reverse replay

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Tatsuya Haga ◽  
Tomoki Fukai
Keyword(s):  
Sequence Learning ◽  
Spatial Navigation ◽  
Recurrent Network ◽  
Place Cells ◽  
Spike Timing ◽  
Directed Path ◽  
Short Term ◽  
Reward Seeking ◽  
Sequential Activation ◽  
First Time

Reverse replay of hippocampal place cells occurs frequently at rewarded locations, suggesting its contribution to goal-directed path learning. Symmetric spike-timing dependent plasticity (STDP) in CA3 likely potentiates recurrent synapses for both forward (start to goal) and reverse (goal to start) replays during sequential activation of place cells. However, how reverse replay selectively strengthens forward synaptic pathway is unclear. Here, we show computationally that firing sequences bias synaptic transmissions to the opposite direction of propagation under symmetric STDP in the co-presence of short-term synaptic depression or afterdepolarization. We demonstrate that significant biases are created in biologically realistic simulation settings, and this bias enables reverse replay to enhance goal-directed spatial memory on a W-maze. Further, we show that essentially the same mechanism works in a two-dimensional open field. Our model for the first time provides the mechanistic account for the way reverse replay contributes to hippocampal sequence learning for reward-seeking spatial navigation.

scholarly journals Masking reduces orientation selectivity in rat visual cortex

2016 ◽  
Vol 116 (5) ◽  
pp. 2331-2341 ◽  
Author(s):  
Dasuni S. Alwis ◽  
Katrina L. Richards ◽  
Nicholas S. C. Price
Keyword(s):  
Visual Cortex ◽  
Firing Rate ◽  
Visual Masking ◽  
Stimulus Onset ◽  
Orientation Selectivity ◽  
Neuronal Responses ◽  
Neural Integration ◽  
Neuronal Representation ◽  
Onset Asynchrony ◽  
First Time

In visual masking the perception of a target stimulus is impaired by a preceding (forward) or succeeding (backward) mask stimulus. The illusion is of interest because it allows uncoupling of the physical stimulus, its neuronal representation, and its perception. To understand the neuronal correlates of masking, we examined how masks affected the neuronal responses to oriented target stimuli in the primary visual cortex (V1) of anesthetized rats ( n = 37). Target stimuli were circular gratings with 12 orientations; mask stimuli were plaids created as a binarized sum of all possible target orientations. Spatially, masks were presented either overlapping or surrounding the target. Temporally, targets and masks were presented for 33 ms, but the stimulus onset asynchrony (SOA) of their relative appearance was varied. For the first time, we examine how spatially overlapping and center-surround masking affect orientation discriminability (rather than visibility) in V1. Regardless of the spatial or temporal arrangement of stimuli, the greatest reductions in firing rate and orientation selectivity occurred for the shortest SOAs. Interestingly, analyses conducted separately for transient and sustained target response components showed that changes in orientation selectivity do not always coincide with changes in firing rate. Given the near-instantaneous reductions observed in orientation selectivity even when target and mask do not spatially overlap, we suggest that monotonic visual masking is explained by a combination of neural integration and lateral inhibition.

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