387 research outputs found
Adaptation-Dependent Synchronous Activity Contributes to Receptive Field Size Change of Bullfrog Retinal Ganglion Cell
Nearby retinal ganglion cells of similar functional subtype have a tendency to discharge spikes in synchrony. The synchronized activity is involved in encoding some aspects of visual input. On the other hand, neurons always continuously adjust their activities in adaptation to some features of visual stimulation, including mean ambient light, contrast level, etc. Previous studies on adaptation were primarily focused on single neuronal activity, however, it is also intriguing to investigate the adaptation process in population neuronal activities. In the present study, by using multi-electrode recording system, we simultaneously recorded spike discharges from a group of dimming detectors (OFF-sustained type ganglion cells) in bullfrog retina. The changes in receptive field properties and synchronization strength during contrast adaptation were analyzed. It was found that, when perfused using normal Ringer's solution, single neuronal receptive field size was reduced during contrast adaptation, which was accompanied by weakening in synchronization strength between adjacent neurons' activities. When dopamine (1 ”M) was applied, the adaptation-related receptive field area shrinkage and synchronization weakening were both eliminated. The activation of D1 receptor was involved in the adaptation-related modulation of synchronization and receptive field. Our results thus suggest that the size of single neuron's receptive field is positively related to the strength of its synchronized activity with its neighboring neurons, and the dopaminergic pathway is responsible for the modulation of receptive field property and synchronous activity of the ganglion cells during the adaptation process
Identification of a Circadian Clock-Controlled Neural Pathway in the Rabbit Retina
Background: Although the circadian clock in the mammalian retina regulates many physiological processes in the retina, it is not known whether and how the clock controls the neuronal pathways involved in visual processing. Methodology/Principal Findings: By recording the light responses of rabbit axonless (A-type) horizontal cells under darkadapted conditions in both the day and night, we found that rod input to these cells was substantially increased at night under control conditions and following selective blockade of dopamine D2, but not D1, receptors during the day, so that the horizontal cells responded to very dim light at night but not in the day. Using neurobiotin tracer labeling, we also found that the extent of tracer coupling between rabbit rods and cones was more extensive during the night, compared to the day, and more extensive in the day following D 2 receptor blockade. Because A-type horizontal cells make synaptic contact exclusively with cones, these observations indicate that the circadian clock in the mammalian retina substantially increases rod input to A-type horizontal cells at night by enhancing rod-cone coupling. Moreover, the clock-induced increase in D2 receptor activation during the day decreases rod-cone coupling so that rod input to A-type horizontal cells is minimal. Conclusions/Significance: Considered together, these results identify the rod-cone gap junction as a key site in mammals through which the retinal clock, using dopamine activation of D2 receptors, controls signal flow in the day and night fro
The high-energy Sun - probing the origins of particle acceleration on our nearest star
As a frequent and energetic particle accelerator, our Sun provides us with an excellent astrophysical laboratory for understanding the fundamental process of particle acceleration. The exploitation of radiative diagnostics from electrons has shown that acceleration operates on sub-second time scales in a complex magnetic environment, where direct electric fields, wave turbulence, and shock waves all must contribute, although precise details are severely lacking. Ions were assumed to be accelerated in a similar manner to electrons, but Îł-ray imaging confirmed that emission sources are spatially separated from X-ray sources, suggesting distinctly different acceleration mechanisms. Current X-ray and Îł-ray spectroscopy provides only a basic understanding of accelerated particle spectra and the total energy budgets are therefore poorly constrained. Additionally, the recent detection of relativistic ion signatures lasting many hours, without an electron counterpart, is an enigma. We propose a single platform to directly measure the physical conditions present in the energy release sites and the environment in which the particles propagate and deposit their energy. To address this fundamental issue, we set out a suite of dedicated instruments that will probe both electrons and ions simultaneously to observe; high (seconds) temporal resolution photon spectra (4Â keV â 150Â MeV) with simultaneous imaging (1Â keV â 30Â MeV), polarization measurements (5â1000Â keV) and high spatial and temporal resolution imaging spectroscopy in the UV/EUV/SXR (soft X-ray) regimes. These instruments will observe the broad range of radiative signatures produced in the solar atmosphere by accelerated particles
Actions in Practice: On details in collections
Several of the contributions to the Lynch et al. Special issue make the claim that conversation- analytic research into epistemics is âroutinely crafted at the expense of actual, produced and constitutive detail, and what that detail may show usâ. Here, we seek to address the inappositeness of this critique by tracing precisely how it is that recognizable actions emerge from distinct practices of interaction. We begin by reviewing some of the foundational tenets of conversation-analytic theory and method â including the relationship between position and composition, and the making of collections â as these appear to be primary sources of confusion for many of the contributors to the Lynch et al. Special Issue. We then target some of the specific arguments presented in the Special Issue, including the alleged âover-hearerâsâ writing of metrics, the provision of so- called âalternativeâ analyses and the supposed âcraftingâ of generalizations in epistemics research. In addition, in light of Lynchâs more general assertion that conversation analysis (CA) has recently been experiencing a ârapprochementâ with what he disparagingly refers to as the âjuggernautâ of linguistics, we discuss the specific expertise that linguists have to offer in analyzing particular sorts of interactional detail. The article as a whole thus illustrates that, rather than being produced âat the expense of actual, produced and constitutive detailâ, conversation-analytic findings â including its work in epistemics â are unambiguously anchored in such detail. We conclude by offering our comments as to the link between CA and linguistics more generally, arguing that this relationship has long proven to be â and indeed continues to be â a mutually beneficial one
Asteroseismology and Interferometry
Asteroseismology provides us with a unique opportunity to improve our
understanding of stellar structure and evolution. Recent developments,
including the first systematic studies of solar-like pulsators, have boosted
the impact of this field of research within Astrophysics and have led to a
significant increase in the size of the research community. In the present
paper we start by reviewing the basic observational and theoretical properties
of classical and solar-like pulsators and present results from some of the most
recent and outstanding studies of these stars. We centre our review on those
classes of pulsators for which interferometric studies are expected to provide
a significant input. We discuss current limitations to asteroseismic studies,
including difficulties in mode identification and in the accurate determination
of global parameters of pulsating stars, and, after a brief review of those
aspects of interferometry that are most relevant in this context, anticipate
how interferometric observations may contribute to overcome these limitations.
Moreover, we present results of recent pilot studies of pulsating stars
involving both asteroseismic and interferometric constraints and look into the
future, summarizing ongoing efforts concerning the development of future
instruments and satellite missions which are expected to have an impact in this
field of research.Comment: Version as published in The Astronomy and Astrophysics Review, Volume
14, Issue 3-4, pp. 217-36
Cyclic game dynamics driven by iterated reasoning
Recent theories from complexity science argue that complex dynamics are
ubiquitous in social and economic systems. These claims emerge from the
analysis of individually simple agents whose collective behavior is
surprisingly complicated. However, economists have argued that iterated
reasoning--what you think I think you think--will suppress complex dynamics by
stabilizing or accelerating convergence to Nash equilibrium. We report stable
and efficient periodic behavior in human groups playing the Mod Game, a
multi-player game similar to Rock-Paper-Scissors. The game rewards subjects for
thinking exactly one step ahead of others in their group. Groups that play this
game exhibit cycles that are inconsistent with any fixed-point solution
concept. These cycles are driven by a "hopping" behavior that is consistent
with other accounts of iterated reasoning: agents are constrained to about two
steps of iterated reasoning and learn an additional one-half step with each
session. If higher-order reasoning can be complicit in complex emergent
dynamics, then cyclic and chaotic patterns may be endogenous features of
real-world social and economic systems.Comment: 8 pages, 4 figures, and supplementary informatio
A barrier to homologous recombination between sympatric strains of the cooperative soil bacterium Myxococcus xanthus
The bacterium Myxococcus xanthus glides through soil in search of prey microbes, but when food
sources run out, cells cooperatively construct and sporulate within multicellular fruiting bodies.
M. xanthus strains isolated from a 16 Ă 16-cm-scale patch of soil were previously shown to have
diversified into many distinct compatibility types that are distinguished by the failure of swarming
colonies to merge upon encounter. We sequenced the genomes of 22 isolates from this population
belonging to the two most frequently occurring multilocus sequence type (MLST) clades to trace
patterns of incipient genomic divergence, specifically related to social divergence. Although
homologous recombination occurs frequently within the two MLST clades, we find an almost
complete absence of recombination events between them. As the two clades are very closely related
and live in sympatry, either ecological or genetic barriers must reduce genetic exchange between
them. We find that the rate of change in the accessory genome is greater than the rate of amino-acid
substitution in the core genome. We identify a large genomic tract that consistently differs between
isolates that do not freely merge and therefore is a candidate region for harbouring gene(s)
responsible for self/non-self discrimination
Molecular, microbiological and clinical characterization of Clostridium difficile isolates from tertiary care hospitals in Colombia
In Colombia, the epidemiology and circulating genotypes of Clostridium difficile have not yet been described. Therefore, we molecularly characterized clinical isolates of C.difficile from patients with suspicion of C.difficile infection (CDI) in three tertiary care hospitals. C.difficile was isolated from stool samples by culture, the presence of A/B toxins were detected by enzyme immunoassay, cytotoxicity was tested by cell culture and the antimicrobial susceptibility determined. After DNA extraction, tcdA, tcdB and binary toxin (CDTa/CDTb) genes were detected by PCR, and PCR-ribotyping performed. From a total of 913 stool samples collected during 2013â2014, 775 were included in the study. The frequency of A/B toxins-positive samples was 9.7% (75/775). A total of 143 isolates of C.difficile were recovered from culture, 110 (76.9%) produced cytotoxic effect in cell culture, 100 (69.9%) were tcdA+/tcdB+, 11 (7.7%) tcdA-/tcdB+, 32 (22.4%) tcdA-/tcdB- and 25 (17.5%) CDTa+/CDTb+. From 37 ribotypes identified, ribotypes 591 (20%), 106 (9%) and 002 (7.9%) were the most prevalent; only one isolate corresponded to ribotype 027, four to ribotype 078 and four were new ribotypes (794,795, 804,805). All isolates were susceptible to vancomycin and metronidazole, while 85% and 7.7% were resistant to clindamycin and moxifloxacin, respectively. By multivariate analysis, significant risk factors associated to CDI were, staying in orthopedic service, exposure to third-generation cephalosporins and staying in an ICU before CDI symptoms; moreover, steroids showed to be a protector factor. These results revealed new C. difficile ribotypes and a high diversity profile circulating in Colombia different from those reported in America and European countries
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