3,493 research outputs found
Source monitoring and memory confidence in schizophrenia
BACKGROUND: The present study attempted to extend previous research on source monitoring deficits in schizophrenia. We hypothesized that patients would show a bias to attribute self-generated words to an external source. Furthermore, it was expected that schizophrenic patients would be overconfident regarding false memory attributions. METHOD: Thirty schizophrenic and 21 healthy participants were instructed to provide a semantic association for 20 words. Subsequently, a list was read containing experimenter- and self-generated words as well as new words. The subject was required to identify each item as old/new, name the source. and state the degree of confidence for the source attribution. RESULTS: Schizophrenic patients displayed a significantly increased number of source attribution errors and were significantly more confident than controls that a false source attribution response was true. The latter bias was ameliorated by higher doses of neuroleptics. CONCLUSIONS: It is inferred that a core cognitive deficit underlying schizophrenia is a failure to distinguish false from true mnestic contents
Doctor of Philosophy
dissertationDetermining the health impacts of a nutritional regimen, suspected toxicant or other treatment is often a difficult task in both the realms of safety assessment and basic research. There are far too many examples of agents, once considered safe, found later through epidemiology (or other means) to cause adverse health effects. To prevent such experimentation on ourselves there is a great societal need for broad, sensitive assays able to detect toxicity at human-relevant exposure levels. Similarly, basic researchers often lack the experimental tools necessary to determine if a treatment adversely impacts the health of their model organism. We argue that these problems can be partially solved by using house mice in the crucible of their natural setting where they are challenged daily by the very tasks that have shaped them for millennia. Quantifying the lifelong fitness of experimentally treated animals directly competing with control individuals offers a sensitive and broad approach for detecting adverse health effects. We refer to this approach as an Organismal Performance Assay (OPA). To illustrate the effectiveness of OPAs, herein we apply them for detecting adverse health consequences of nutritional and toxic exposures. First, using OPAs we capture adverse health impacts (decreased survival, competitive ability and reproduction) from consuming 12.5% kcal of fructose; this finding now represent the lowest observed adverse effect level for dietary fructose. Next, we apply OPAs to determine if differential health impacts occur due to the consumption of one, or the other, of the two common types of added sugar, high fructose corn syrup (fructose and glucose monosaccharides) or table sugar (sucrose, which is a disaccharide of fructose and glucose), and show that the high fructose corn syrup diet increases mortality and decreases reproduction of female mice compared to sucrose, providing the first experimental evidence that the two most common forms of caloric sweeteners have differential health impacts. Next, we use OPAs to determine if an acute exposure to 3mg/kg of amine-terminated generation seven poly amido-amine dendrimers, the current maximum tolerated dose, is actually toxic and find that it is not. Finally, to address the criticism that OPAs do not lead to the underlying mechanisms of observed organismal outcomes, we illustrate the discovery of the molecular basis of the first phenomenon revealed using OPAs, major histocompatibility complex (MHC)-based mating preferences, which is done in the context of a review paper on the role of MHC during social communication
Microbial community ecology of marine methane seeps
The detailed investigation of microbial communities, e.g. of soil or hydrothermal vent ecosystems, greatly improved our understanding of the diversity, habitat preferences and functions of microorganisms and their impact on global element cycles. The aim of this thesis was a detailed analysis of the diversity, abundance and distribution of micoorganisms at marine methane seeps and the mechanisms that govern community assembly at these sites. The seep ecosystems were investigated using geochemical analyses, gene libraries, pyrosequencing, community fingerprinting and fluorescence in situ hybridization. Cold seep ecosystems hosted distinct microbial communities that differed from those of the surrounding seabed and were unique microbial habitat patches in the deep sea. The communities also greatly differed between seeps, covered broad ranges of richness and evenness and showed high degrees of endemism. However, despite the differences all seeps were inhabited by certain organisms the cold seep microbiome - including key functional clades of anaerobic methane oxidizing archaea (ANME) and sulfate-reducing bacteria. Additionally, aerobic methanotrophs and thiotrophs were found at all seeps where oxygen was present. These key functional clades seemed to be influenced by environmental parameters, such as temperature, fluid flux, sediment depth and faunal activity. Bioirrigation by ampharetid tubeworms, for instance, created a habitat for aerobic Methylococcales, whereas vesicomyid clams seemed to favor the establishment of the clade ANME-2c. Thus, niche-based processes played an important role for the community assembly at seep ecosystems. However, most of the seeps seemed to be clearly dominated by a few, globally distributed operational taxonomic units at 97% 16S rRNA gene identity (OTU0.03) of each key functional clade. Some of these OTU0.03 were rare at some seep ecosystems and abundant at others. Moreover, some findings suggested that rare organisms became abundant because the environmental conditions at the seep changed supporting the importance of species sorting at seep communities. Finally, the succession of microbial communities and the emergence of ecosystem function at a cold seep were monitored showing that it may take years to develop fully functioning communities that efficiently remove the potential greenhouse gas methane. Overall this work may help to resolve the mysteries of microbial community ecology at cold seep ecosystems
MHC signaling during social communication
Journal ArticleThe major histocompatibility complex (MHC) has been known to play a critical role in immune recognition since the 1950s. It was a surprise, then, in the 1970s when the first report appeared indicating MHC might also function in social signaling. Since this seminal discovery, MHC signaling has been found throughout vertebrates and its known functions have expanded beyond mate choice to include a suite of behaviors from kinābiased cooperation, parentāprogeny recognition to pregnancy block. The widespread occurrence of MHC in social signaling has revealed conserved behavioralāgenetic mechanisms that span vertebrates and includes humans. The identity of the signal's chemical constituents and the receptors responsible for the perception of the signal have remained elusive, but recent advances have enabled the identification of the key components of the behavioral circuit. In this chapter we organize recent findings from the literature and discuss them in relation to four nonmutually exclusive models wherein MHC functions as a signal of (i) individuality, (ii) relatedness, (iii) genetic compatibility and (iv) quality. We also synthesize current mechanistic studies, showing how knowledge about the molecular basis of MHC signaling can lead to elegant and informative experimental manipulations. Finally, we discuss current evidence relating to the primordial functions of the MHC, including the possibility that its role in social signaling may be ancestral to its central role in adaptive immunity
Structural, magnetic, electric, dielectric, and thermodynamic properties of multiferroic GeV4S8
The lacunar spinel GeV4S8 undergoes orbital and ferroelectric ordering at the
Jahn-Teller transition around 30 K and exhibits antiferromagnetic order below
about 14 K. In addition to this orbitally driven ferroelectricity, lacunar
spinels are an interesting material class, as the vanadium ions form V4
clusters representing stable molecular entities with a common electron
distribution and a well-defined level scheme of molecular states resulting in a
unique spin state per V4 molecule. Here we report detailed x-ray, magnetic
susceptibility, electrical resistivity, heat capacity, thermal expansion, and
dielectric results to characterize the structural, electric, dielectric,
magnetic, and thermodynamic properties of this interesting material, which also
exhibits strong electronic correlations. From the magnetic susceptibility, we
determine a negative Curie-Weiss temperature, indicative for antiferromagnetic
exchange and a paramagnetic moment close to a spin S = 1 of the V4 molecular
clusters. The low-temperature heat capacity provides experimental evidence for
gapped magnon excitations. From the entropy release, we conclude about strong
correlations between magnetic order and lattice distortions. In addition, the
observed anomalies at the phase transitions also indicate strong coupling
between structural and electronic degrees of freedom. Utilizing dielectric
spectroscopy, we find the onset of significant dispersion effects at the polar
Jahn-Teller transition. The dispersion becomes fully suppressed again with the
onset of spin order. In addition, the temperature dependencies of dielectric
constant and specific heat possibly indicate a sequential appearance of orbital
and polar order.Comment: 15 pages, 9 figure
Polar and magnetic order in GaV4Se8
In the present work, we provide results from specific heat, magnetic
susceptibility, dielectric constant, ac conductivity, and electrical
polarization measurements performed on the lacunar spinel GaV4Se8. With
decreasing temperature, we observe a transition from the paraelectric and
paramagnetic cubic state into a polar, probably ferroelectric state at 42 K
followed by magnetic ordering at 18 K. The polar transition is likely driven by
the Jahn-Teller effect due to the degeneracy of the V4 cluster orbitals. The
excess polarization arising in the magnetic phase indicates considerable
magnetoelectric coupling. Overall, the behavior of GaV4Se8 in many respects is
similar to that of the skyrmion host GaV4S8, exhibiting a complex interplay of
orbital, spin, lattice, and polar degrees of freedom. However, its dielectric
behavior at the polar transition markedly differs from that of the Jahn-Teller
driven ferroelectric GeV4S8, which can be ascribed to the dissimilar electronic
structure of the Ge compound.Comment: 7 pages, 6 figures. Revised version according to suggestions of
referee
Electronic bulk and domain wall properties in B-site doped hexagonal ErMnO
Acceptor and donor doping is a standard for tailoring semiconductors. More
recently, doping was adapted to optimize the behavior at ferroelectric domain
walls. In contrast to more than a century of research on semiconductors, the
impact of chemical substitutions on the local electronic response at domain
walls is largely unexplored. Here, the hexagonal manganite ErMnO is donor
doped with Ti. Density functional theory calculations show that
Ti goes to the B-site, replacing Mn. Scanning probe microscopy
measurements confirm the robustness of the ferroelectric domain template. The
electronic transport at both macro- and nanoscopic length scales is
characterized. The measurements demonstrate the intrinsic nature of emergent
domain wall currents and point towards Poole-Frenkel conductance as the
dominant transport mechanism. Aside from the new insight into the electronic
properties of hexagonal manganites, B-site doping adds an additional degree of
freedom for tuning the domain wall functionality
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