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Search Results: 1 - 10 of 201792 matches for " Stephen D. Auger "
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Retrosplenial Cortex Codes for Permanent Landmarks
Stephen D. Auger, Sinéad L. Mullally, Eleanor A. Maguire
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0043620
Abstract: Landmarks are critical components of our internal representation of the environment, yet their specific properties are rarely studied, and little is known about how they are processed in the brain. Here we characterised a large set of landmarks along a range of features that included size, visual salience, navigational utility, and permanence. When human participants viewed images of these single landmarks during functional magnetic resonance imaging (fMRI), parahippocampal cortex (PHC) and retrosplenial cortex (RSC) were both engaged by landmark features, but in different ways. PHC responded to a range of landmark attributes, while RSC was engaged by only the most permanent landmarks. Furthermore, when participants were divided into good and poor navigators, the latter were significantly less reliable at identifying the most permanent landmarks, and had reduced responses in RSC and anterodorsal thalamus when viewing such landmarks. The RSC has been widely implicated in navigation but its precise role remains uncertain. Our findings suggest that a primary function of the RSC may be to process the most stable features in an environment, and this could be a prerequisite for successful navigation.
Spectral Domain OCT: An Aid to Diagnosis and Surgical Planning of Retinal Detachments
Graham Auger,Stephen Winder
Journal of Ophthalmology , 2011, DOI: 10.1155/2011/725362
Abstract: Regmatogenous retinal detachments need prompt intervention particularly when macula is on. Unfortunately this is not always easy to ascertain clinically and the chronicity of the event is often muddled in patient's histories. Developments in optical coherence tomography (OCT) have allowed high-resolution axial scans which have enabled the characterisation of retinal changes in retinal detachments. In this paper, we show the changes in retinal morphology observed by spectral domain OCT and how this can be used to plan appropriate surgical intervention.
Spectral Domain OCT: An Aid to Diagnosis and Surgical Planning of Retinal Detachments
Graham Auger,Stephen Winder
Journal of Ophthalmology , 2011, DOI: 10.1155/2011/725362
Abstract: Regmatogenous retinal detachments need prompt intervention particularly when macula is on. Unfortunately this is not always easy to ascertain clinically and the chronicity of the event is often muddled in patient's histories. Developments in optical coherence tomography (OCT) have allowed high-resolution axial scans which have enabled the characterisation of retinal changes in retinal detachments. In this paper, we show the changes in retinal morphology observed by spectral domain OCT and how this can be used to plan appropriate surgical intervention. 1. Introduction Rhegmatogenous retinal detachments referred in an acute nature require prompt surgical repair. However, studies have shown that surgery is best done during normal working hours [1]. Given the pressures on theatre use it is important to be able to assess the retinal detachment and to ascertain the urgency of planning surgical intervention. One of the most important features is the involvement of the macula and fovea that is macula on or macula off. In cases of macula-off retinal detachments, visual outcome is less dependent on prompt surgery and surgical correction can be delayed [1]. Macula-on retinal detachments, however, should have their surgery expedited, the main concern being the conversion to a macula-off situation which has a much poorer visual prognosis [1]. The assessment of rhegmatogenous retinal detachments is multifactorial; in an otherwise normal eye visual acuity is an easy measure of macula involvement with the 6/60 patient being macula off and 6/6 macula on [1]. Similarly the onset of symptoms and the age of the retinal detachment is important, as chronic detachments can be more stable and surgery can be safely delayed [1]. Also the extent of detachment and position of the retinal break can also help predict the progression of an acute macula on retinal detachment [1]. However, in certain situations the macula-on or macula-off question is not easily answered; visual acuities may be misleading; examination of the detachment may be difficult due to poor views often due to vitreous hemorrhage and chronicity may be difficult to ascertain in patients with vague histories. High-speed spectral domain optical coherence tomography (OCT) offers a noninvasive tool to evaluate retinal microstructural changes in a number of eye pathologies. Newer systems using spectral domain calculations have improved data acquisition speeds compared with conventional time-domain OCT equipment allowing much greater axial resolution [2]. Given the greater resolution a number of characteristic changes
Altered Dopamine Signaling in Naturally Occurring Maternal Neglect
Stephen C. Gammie, Michelle N. Edelmann, Caleigh Mandel-Brehm, Kimberly L. D'Anna, Anthony P. Auger, Sharon A. Stevenson
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0001974
Abstract: Background Child neglect is the most common form of child maltreatment, yet the biological basis of maternal neglect is poorly understood and a rodent model is lacking. Methodology/Principal Findings The current study characterizes a population of mice (MaD1) which naturally exhibit maternal neglect (little or no care of offspring) at an average rate of 17% per generation. We identified a set of risk factors that can predict future neglect of offspring, including decreased self-grooming and elevated activity. At the time of neglect, neglectful mothers swam significantly more in a forced swim test relative to nurturing mothers. Cross-fostered offspring raised by neglectful mothers in turn exhibit increased expression of risk factors for maternal neglect and decreased maternal care as adults, suggestive of possible epigenetic contributions to neglect. Unexpectedly, offspring from neglectful mothers elicited maternal neglect from cross-fostered nurturing mothers, suggesting that factors regulating neglect are not solely within the mother. To identify a neurological pathway underlying maternal neglect, we examined brain activity in neglectful and nurturing mice. c-Fos expression was significantly elevated in neglectful relative to nurturing mothers in the CNS, particularly within dopamine associated areas, such as the zona incerta (ZI), ventral tegmental area (VTA), and nucleus accumbens. Phosphorylated tyrosine hydroxylase (a marker for dopamine production) was significantly elevated in ZI and higher in VTA (although not significantly) in neglectful mice. Tyrosine hydroxylase levels were unaltered, suggesting a dysregulation of dopamine activity rather than cell number. Phosphorylation of DARPP-32, a marker for dopamine D1-like receptor activation, was elevated within nucleus accumbens and caudate-putamen in neglectful versus nurturing dams. Conclusions/Significance These findings suggest that atypical dopamine activity within the maternal brain, especially within regions involved in reward, is involved in naturally occurring neglect and that MaD1 mice are a useful model for understanding the basis of naturally occurring neglect.
Calibration of the Pierre Auger fluorescence detector
M. D. Roberts,for the Auger Collaboration
Physics , 2003,
Abstract: The absolute calibration of an air fluorescence detector (FD) is an important element in correctly determining the energy of detected cosmic rays. The absolute calibration relates the flux of photons of a given wavelength at the detector aperture to the electronic signal recorded by the FD data acquisition system. For the Auger FDs, the primary absolute calibration method uses a diffusive surface which is placed in front of a telescope aperture to uniformly illuminate the telescope field of view with a known light signal. This single-wavelength measurement (375 nm) will be made at intervals of several months until the stability of the telescopes is determined. The relative wavelength dependence of the calibration is determined through independent measurements. The error in absolute calibration at a single wavelength is estimated to be less than 10%. Two other absolute calibration methods are used to provide an independent verification of the primary measurement. The stability of the calibration with time is monitored nightly by a relative calibration system. In this paper we will provide descriptions of the absolute and relative calibration methods used by the Auger air fluorescence observatory. Results from the calibration of the Auger Engineering Array telescopes will also be presented.
Energy, the driving force behind good and ill health
Vasu D. Appanna,Christopher Auger,Joseph Lemire
Frontiers in Cell and Developmental Biology , 2014, DOI: 10.3389/fcell.2014.00028
Abstract:
Effects of Phaeomoniella chlamydospora ana Phaeoacremonium aleophilum on grapevine rootstocks
Díaz,Gonzalo A; Esterio,Marcela; Auger,Jaime;
Ciencia e investigación agraria , 2009, DOI: 10.4067/S0718-16202009000300005
Abstract: cuttings of five grapevine (vitis vinifera) rootstocks were wounded and immediately inoculated with suspensions (approximately 5x103 conidia- ml-1) of either phaeomoniella chlamydospora, phaeoacremonium aleophilum or a mixture of both species. the presence of these endophyte fungi affected the quality of each of the five rootstocks. among the roostocks investigated in this study, 1103p and 101-14 mg were less susceptible to the infection caused by pa. chlamydospora wd pm. aleophillum.
Adaptive Optics Observations of B0128+437: A Low-Mass, High-Redshift Gravitational Lens
David J. Lagattuta,Matthew W. Auger,Christopher D. Fassnacht
Physics , 2009, DOI: 10.1088/2041-8205/716/2/L185
Abstract: We use high-resolution adaptive optics (AO) imaging on the Keck II telescope to study the gravitational lens B0128+437 in unprecedented detail, allowing us to resolve individual lensed quasar components and, for the first time, detect and measure properties of the lensing galaxy. B0128+437 is a small separation lens with known flux-ratio and astrometric anomalies. We discuss possible causes for these anomalies, including the presence of substructure in the lensing galaxy, propagation effects due to dust and a turbulent interstellar medium, and gravitational microlensing. This work on B0128 demonstrates that AO will be an essential tool for studying the many new small-separation lenses expected from future surveys.
Radio-mode feedback in local AGNs: dependence on the central black hole parameters
W. Ishibashi,M. W. Auger,D. Zhang,A. C. Fabian
Physics , 2014, DOI: 10.1093/mnras/stu1236
Abstract: Radio mode feedback, in which most of the energy of an active galactic nucleus (AGN) is released in a kinetic form via radio-emitting jets, is thought to play an important role in the maintenance of massive galaxies in the present-day Universe. We study the link between radio emission and the properties of the central black hole in a large sample of local radio galaxies drawn from the Sloan Digital Sky Survey (SDSS), based on the catalogue of Best and Heckman (2012). Our sample is mainly dominated by massive black holes (mostly in the range $10^8-10^9 M_{\odot}$) accreting at very low Eddington ratios (typically $\lambda < 0.01$). In broad agreement with previously reported trends, we find that radio galaxies are preferentially associated with the more massive black holes, and that the radio loudness parameter seems to increase with decreasing Eddington ratio. We compare our results with previous studies in the literature, noting potential biases. The majority of the local radio galaxies in our sample are currently in a radiatively inefficient accretion regime, where kinetic feedback dominates over radiative feedback. We discuss possible physical interpretations of the observed trends in the context of a two-stage feedback process involving a transition in the underlying accretion modes.
Studies on the actin-binding protein HS1 in platelets
Steven G Thomas, Simon DJ Calaminus, Jocelyn M Auger, Stephen P Watson, Laura M Machesky
BMC Cell Biology , 2007, DOI: 10.1186/1471-2121-8-46
Abstract: The present results demonstrate that HS1 is not required for platelet activation, shape change or aggregation. Platelets from HS1-/- mice spread normally on a variety of adhesion proteins and have normal F-actin and Arp2/3 complex distributions. Clot retraction, an actin-dependent process, is also normal in these mice. Platelet aggregation and secretion is indistinguishable between knock out and littermates and there is no increase in bleeding using the tail bleeding assay.This study concludes that HS1 does not play a major role in platelet function. It is possible that a role for HS1 is masked by the presence of cortactin.The platelet is highly dependent upon its actin cytoskeleton for proper functioning. Dramatic re-arrangements of the actin cytoskeleton mediates spreading on matrix proteins and is required for normal thrombus formation [1,2]. At rest, the discoid shape of a platelet is maintained by a microtubule coil, a spectrin-based skeleton immediately below the plasma membrane, and a network of 2000 – 5000 actin filaments held rigid by the cross-linking proteins filamin and α-actinin [3-5]. Following Ca2+ elevation, the actin-severing protein gelsolin is released from barbed ends leading to relaxing of the discoid shape and a large increase in the number of free barbed ends for polymerisation [6]. Concomitant activation of the Arp2/3 complex, a seven-membered protein complex which nucleates actin filaments, leads to a massive increase in the F-actin content of platelets. This provides the protrusive force for filopodia and lamellipodia formation that gives the platelet its characteristic spread morphology [7].The Arp2/3 complex is regulated by a number of proteins which allow for tight spatial and temporal regulation of its activity, including haematopoietic lineage cell-specific protein 1 (HS1) and its homologue cortactin (for reviews see [8,9]) (Figure 1A). HS1 is expressed in cells of a haematopoietic lineage, whereas cortactin is ubiquitously expressed.
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