Recollection is thought to be the hallmark of episodic memory. Here we provide evidence that the hippocampus binds together the diverse elements forming an event, allowing holistic recollection via ...pattern completion of all elements. Participants learn complex 'events' from multiple overlapping pairs of elements, and are tested on all pairwise associations. At encoding, element 'types' (locations, people and objects/animals) produce activation in distinct neocortical regions, while hippocampal activity predicts memory performance for all within-event pairs. When retrieving a pairwise association, neocortical activity corresponding to all event elements is reinstated, including those incidental to the task. Participant's degree of incidental reinstatement correlates with their hippocampal activity. Our results suggest that event elements, represented in distinct neocortical regions, are bound into coherent 'event engrams' in the hippocampus that enable episodic recollection--the re-experiencing or holistic retrieval of all aspects of an event--via a process of hippocampal pattern completion and neocortical reinstatement.
The marine biogeochemical cycle of Ba is thought to be controlled by particulate BaSO4 (barite) precipitation associated with the microbial oxidation of organic carbon and its subsequent dissolution ...in the BaSO4-undersaturated water column. Despite many of these processes being largely unique to Ba cycling, concentrations of Ba and Si in seawater exhibit a strong linear correlation. The reasons for this correlation are ambiguous, as are the depth ranges corresponding to the most active BaSO4 cycling and the intermediate sources of Ba to particulate BaSO4. Stable isotopic analyses of dissolved Ba in seawater should help address these issues, as Ba-isotopic compositions are predicted to be sensitive to the physical and biogeochemical process that cycle Ba. We report a new methodology for the determination of dissolved Ba-isotopic compositions in seawater and results from a 4500 m depth profile in the South Atlantic at 39.99° S, 0.92° E that exhibit oceanographically-consistent variation with depth. These data reveal that water masses obtain their Ba and Ba-isotopic signatures when at or near the surface, which relates to the cycling of marine BaSO4. The shallow origin of these signatures requires that the substantial Ba-isotopic variations in the bathypelagic zone were inherited from when those deep waters were last ventilated. Indeed, the water column below 600 m is well explained by conservative mixing of water masses with distinct Ba and Ba-isotopic compositions. This leads us to conclude that large scale oceanic circulation is important for sustaining the similar oceanographic distributions of Ba and Si in the South Atlantic, and possibly elsewhere. These data demonstrate that the processes of organic carbon oxidation, BaSO4 cycling, and Ba-isotopic fractionation in seawater are closely coupled, such that Ba-isotopic analyses harbor great potential as a tracer of the carbon cycle in the modern and paleo-oceans.
•First full seawater depth profile of co-located Ba–δ138/134BaNIST.•Origin of Ba-isotopic variations are best explained by barite cycling.•Regional circulation strongly influences depth structure of δ138/134BaNIST.•Data establish a baseline of Ba-isotopic variability in the marine realm.
Programmed self-assembly of well-defined molecular building blocks enables the fabrication of precisely structured nanomaterials. In this work, we explore a new class of giant polymeric surfactants ...(M n = (0.7–4.4) × 106 g/mol) with bottlebrush architecture and show that their persistent molecular shape leads to the formation of uniform aggregates in a predictable manner. Amphiphilic bottlebrush block copolymers containing polylactide (PLA) and poly(ethylene oxide) (PEO) side chains were synthesized by a grafting-from method, and their self-assembly in aqueous environment was studied by cryogenic transmission electron microscopy. The produced micelle structures with varying interfacial curvatures and core radii (19–55 nm) boasted rod-like hydrophilic PEO brushes protruding from the hydrophobic PLA cores normal to the interface. Highly uniform spherical micelles with low dispersities were obtained from bottlebrush amphiphiles with packing parameters of ∼0.3, estimated from the polymer structural data. Long cylindrical micelles and other nonspherical aggregates were observed for the first time for compositionally less asymmetric bottlebrush surfactants. Critical micelle concentration values of 1 nM, measured for PEO-rich bottlebrush amphiphiles, indicated an enhanced thermodynamic stability of the produced micelle aggregates. Shape-dependent assembly of bottlebrush surfactants allows for the rational fabrication of a range of micelle structures in narrow morphological windows.
Grid cells in the entorhinal cortex (EC) of rodents 1 and humans 2 fire in a hexagonally distributed spatially periodic manner. In concert with other spatial cells in the medial temporal lobe (MTL) ...3–6, they provide a representation of our location within an environment 7, 8 and are specifically thought to allow the represented location to be updated by self-motion 9. Grid-like signals have been seen throughout the autobiographical memory system 10, suggesting a much more general role in memory 11, 12. Grid cells may allow us to move our viewpoint in imagination 13, a useful function for goal-directed navigation and planning 12, 14–16, and episodic future thinking more generally 17, 18. We used fMRI to provide evidence for similar grid-like signals in human entorhinal cortex during both virtual navigation and imagined navigation of the same paths. We show that this signal is present in periods of active navigation and imagination, with a similar orientation in both and with the specifically 6-fold rotational symmetry characteristic of grid cell firing. We therefore provide the first evidence suggesting that grid cells are utilized during movement of viewpoint within imagery, potentially underpinning our more general ability to mentally traverse possible routes in the service of planning and episodic future thinking.
•Grid cells fire in a spatial pattern as mammals actively navigate their environment•Grid cells might move the viewpoint of imagination, aiding goal-directed navigation•Human entorhinal cortex shows a grid-like fMRI signal during imagined navigation•This signal is similar to that seen in the same people during virtual navigation
Horner et al. find a grid-like fMRI signal in human entorhinal cortex as participants imagine navigating through space, similar to that seen during navigation in virtual reality. Thus, grid cells may move the viewpoint of imagination, extending their suggested role in updating self-location during navigation to include dynamic imagery and planning.
Massive sets of stellar spectroscopic observations are rapidly becoming available and these can be used to determine the chemical composition and evolution of the Galaxy with unprecedented precision. ...One of the major challenges in this endeavour involves constructing realistic models of stellar spectra with which to reliably determine stellar abundances. At present, large stellar surveys commonly use simplified models that assume that the stellar atmospheres are approximately in local thermodynamic equilibrium (LTE). To test and ultimately relax this assumption, we have performed non-LTE calculations for 13 different elements (H, Li, C, N, O, Na, Mg, Al, Si, K, Ca, Mn, and Ba), using recent model atoms that have physically-motivated descriptions for the inelastic collisions with neutral hydrogen, across a grid of 3756 1D
MARCS
model atmospheres that spans 3000 ≤
T
eff
∕K ≤ 8000, − 0.5 ≤log
g
∕cm s
−2
≤ 5.5, and − 5 ≤ Fe/H ≤ 1. We present the grids of departure coefficients that have been implemented into the GALAH DR3 analysis pipeline in order to complement the extant non-LTE grid for iron. We also present a detailed line-by-line re-analysis of 50 126 stars from GALAH DR3. We found that relaxing LTE can change the abundances by between − 0.7 dex and + 0.2 dex for different lines and stars. Taking departures from LTE into account can reduce the dispersion in the A/Fe versus Fe/H plane by up to 0.1 dex, and it can remove spurious differences between the dwarfs and giants by up to 0.2 dex. The resulting abundance slopes can thus be qualitatively different in non-LTE, possibly with important implications for the chemical evolution of our Galaxy. The grids of departure coefficients are publicly available and can be implemented into LTE pipelines to make the most of observational data sets from large spectroscopic surveys.
Events are thought to be stored in episodic memory as coherent representations, in which the constituent elements are bound together so that a cue can trigger reexperience of all elements via pattern ...completion. Negative emotional content can strongly influence memory, but opposing theories predict strengthening or weakening of memory coherence. Across a series of experiments, participants imagined a number of person-location-object events with half of the events including a negative element (e.g., an injured person), and memory was tested across all within event associations. We show that the presence of a negative element reduces memory for associations between event elements, including between neutral elements encoded after a negative element. The presence of a negative element reduces the coherence with which a multimodal event is remembered. Our results, supported by a computational model, suggest that coherent retrieval from neutral events is supported by pattern completion, but that negative content weakens associative encoding which impairs this process. Our findings have important implications for understanding the way traumatic events are encoded and support therapeutic strategies aimed at restoring associations between negative content and its surrounding context.
Personally experienced events include multiple elements, such as locations, people, and objects. These events are thought to be stored in episodic memory as coherent representations 1 that allow the ...retrieval of all elements from a partial cue (“pattern completion” 2–6). However, direct evidence for coherent multielement representations is lacking. Their presence would predict that retrieval of one element from an event should be dependent on retrieval of the other elements from that event. If we remember where we were, we should be more likely to remember who we met and what object they gave us. Here we provide evidence for this type of dependency in remembering three-element events. Dependency was seen when all three elements were encoded simultaneously, or when the three overlapping pairwise associations comprising an event were learned on separate trials. However, dependency was only seen in the separated encoding condition when all possible within-event associations were encoded. These results suggest that episodic memories are stored as coherent representations in which associations between all within-event elements allow retrieval via pattern completion. They also show that related experiences encountered at different times can be flexibly integrated into these coherent representations.
•Multielement events are stored as coherent engrams•Retrievals of different associations from the same event are interdependent•Independently encoded overlapping associations can form coherent event engrams•Coherent engrams only form when all within-event associations are encoded
Horner and Burgess present evidence that the multiple associations comprising episodic events are bound within coherent “event engrams.” Related experiences encountered at different times can be flexible integrated into these engrams. Once formed, they are retrieved in an all-or-none manner by a process of pattern completion.
A productivity collapse to end Earth’s Great Oxidation Hodgskiss, Malcolm S. W.; Crockford, Peter W.; Peng, Yongbo ...
Proceedings of the National Academy of Sciences - PNAS,
08/2019, Volume:
116, Issue:
35
Journal Article
Peer reviewed
Open access
It has been hypothesized that the overall size of—or efficiency of carbon export from—the biosphere decreased at the end of the Great Oxidation Event (GOE) (ca. 2,400 to 2,050 Ma). However, the ...timing, tempo, and trigger for this decrease remain poorly constrained. Here we test this hypothesis by studying the isotope geochemistry of sulfate minerals from the Belcher Group, in subarctic Canada. Using insights from sulfur and barium isotope measurements, combined with radiometric ages from bracketing strata, we infer that the sulfate minerals studied here record ambient sulfate in the immediate aftermath of the GOE (ca. 2,018 Ma). These sulfate minerals captured negative triple-oxygen isotope anomalies as low as ∼ −0.8‰. Such negative values occurring shortly after the GOE require a rapid reduction in primary productivity of >80%, although even larger reductions are plausible. Given that these data imply a collapse in primary productivity rather than export efficiency, the trigger for this shift in the Earth system must reflect a change in the availability of nutrients, such as phosphorus. Cumulatively, these data highlight that Earth’s GOE is a tale of feast and famine: A geologically unprecedented reduction in the size of the biosphere occurred across the end-GOE transition.
Decreased ATP correlates with intraocular pressure exposure in the optic nerves of mice with glaucoma. To understand what underlies this energy deficit, we examined mitochondria in the myelinated ...optic nerve axons of the DBA/2J mouse, a model of glaucoma secondary to iris pigment disease, and the DBA/2(wt-gpnmb) control strain.
Mitochondrial length, width, surface area, and health status were measured in 30 electron microscopic fields within the myelinated portion of optic nerves from DBA/2J and DBA/2(wt-gpnmb) mice at 3, 6, and 10 months of age. Protein was isolated from optic nerve for analysis of PINK1, Parkin, LC3-I and -II, and lysosome-associated membrane protein 1 (LAMP1) by Western blot.
The number of mitochondria in DBA/2J optic nerve was increased, and they had significantly smaller surface area. Mitochondria in DBA/2J were closer to the axolemma, more spatially isolated, and their cristae were more disrupted at every age group as compared to DBA/2(wt-gpnmb). Autophagosomes were significantly increased in DBA/2J optic nerve at all ages. Protein analysis showed higher LC3-II to LC3-I ratio in aged DBA/2J optic nerve than in DBA/2(wt-gpnmb). PINK1 and Parkin levels were not statistically different across age groups. LAMP1 was significantly decreased in the aged DBA/2J optic nerve.
Decreased surface area, combined with reduced oxidative capacity in mitochondria from the aged DBA/2J axon, indicate that mitochondrial pathology may contribute to the energy deficit in glaucomatous optic nerve. Though autophagosomes were increased in DBA/2J optic nerve, the increased mitochondria and decreased LAMP1 suggest deteriorating mitochondria are not being efficiently recycled by mitophagy.
Solar System Physics for Exoplanet Research Horner, J.; Kane, S. R.; Marshall, J. P. ...
Publications of the Astronomical Society of the Pacific,
10/2020, Volume:
132, Issue:
1016
Journal Article
Peer reviewed
Open access
Over the past three decades, we have witnessed one of the great revolutions in our understanding of the cosmos-the dawn of the Exoplanet Era. Where once we knew of just one planetary system (the ...solar system), we now know of thousands, with new systems being announced on a weekly basis. Of the thousands of planetary systems we have found to date, however, there is only one that we can study up-close and personal-the solar system. In this review, we describe our current understanding of the solar system for the exoplanetary science community-with a focus on the processes thought to have shaped the system we see today. In section one, we introduce the solar system as a single well studied example of the many planetary systems now observed. In section two, we describe the solar system's small body populations as we know them today-from the two hundred and five known planetary satellites to the various populations of small bodies that serve as a reminder of the system's formation and early evolution. In section three, we consider our current knowledge of the solar system's planets, as physical bodies. In section four we discuss the research that has been carried out into the solar system's formation and evolution, with a focus on the information gleaned as a result of detailed studies of the system's small body populations. In section five, we discuss our current knowledge of planetary systems beyond our own-both in terms of the planets they host, and in terms of the debris that we observe orbiting their host stars. As we learn ever more about the diversity and ubiquity of other planetary systems, our solar system will remain the key touchstone that facilitates our understanding and modeling of those newly found systems, and we finish section five with a discussion of the future surveys that will further expand that knowledge.
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