596 research outputs found
Electrophysiological activation by masked primes: Independence of prime-related and target-related activities
Visual stimuli that are made invisible by metacontrast masking (primes) have a
marked influence on behavioral and psychophysiological measures such as reaction
time (RT) and the lateralized readiness potential (LRP). 4 experiments are
reported that shed light on the effects that masked primes have on the LRP.
Participants had a go-nogo task in which the prime was associated with 1 of 2
responses even if the target required participants to refrain from responding.
To analyze the electrophysiological responses, we computed the LRP and applied
an averaging method separating the activation due to the prime and the target.
The results demonstrated that (a) masked primes activate responses even in a
nogo situation, (b) this prime-related activation is independent of masking, (c)
and is also independent of whether prime and target require the same responses
(congruent condition) or different responses (incongruent condition)
Top-down contingent feature-specific orienting with and without awareness of the visual input
In the present article, the role of endogenous feature-specific orienting for
conscious and unconscious vision is reviewed. We start with an overview of
orienting. We proceed with a review of masking research, and the definition of
the criteria of experimental protocols that demonstrate endogenous and exogenous
orienting, respectively. Against this background of criteria, we assess studies
of unconscious orienting and come to the conclusion that so far studies of
unconscious orienting demonstrated endogenous feature-specific orienting. The
review closes with a discussion of the role of unconscious orienting in action
control
The role of the central stellar cluster in active galactic nuclei. I. Semi-analytical model
The subject of the paper is the role of the massive stellar cluster in the
activity phenomenon and in the structure of active galactic nuclei. We
introduce a simple model of stellar dynamics in the internal part of the
cluster, which allows us to include both the star-disk and the star-star
interactions. It is shown that the properties of the distribution of stars in
the vicinity of the black hole are determined both by the interaction of the
stars with the accretion disk and by the pair gravitational and contact
interaction between the stars. We calculate the distribution of stars in the
central parts of the cluster and we discuss possible effects of stellar
mass-loss due to the star-disk interaction. Finally, we study the implications
of the central cluster for active galactic nuclei activity. We model the broad
line region assuming that the gaseous wakes, following stars after each disk
crossing, play the role of the broad line region clouds, and we calculate the
corresponding line profiles. We also analyze the contribution of star-star and
star-disk collisions to active galactic nuclei variability.Comment: Accepted for publication in Astronomy and Astrophysic
A novel presenilin 1 duplication mutation (Ile168dup) causing Alzheimer's disease associated with myoclonus, seizures and pyramidal features
Mutations in the Presenilin 1 (PSEN1) gene are the most common cause of autosomal dominant familial Alzheimer's disease. We report the clinical, imaging and postmortem findings of kindred carrying a novel duplication mutation (Ile168dup) in the PSEN1 gene. We interpret the pathogenicity of this novel variant and discuss the additional neurological features (pyramidal dysfunction, myoclonus and seizures) that accompanied cognitive decline. This report broadens the clinical phenotype of PSEN1 insertion mutations while also highlighting the importance of considering duplication, insertion and deletion mutations in cases of young onset dementia
Neuro-cognitive mechanisms of conscious and unconscious visual perception: From a plethora of phenomena to general principles
Psychological and neuroscience approaches have promoted much progress in
elucidating the cognitive and neural mechanisms that underlie phenomenal visual
awareness during the last decades. In this article, we provide an overview of
the latest research investigating important phenomena in conscious and
unconscious vision. We identify general principles to characterize conscious and
unconscious visual perception, which may serve as important building blocks for
a unified model to explain the plethora of findings. We argue that in particular
the integration of principles from both conscious and unconscious vision is
advantageous and provides critical constraints for developing adequate
theoretical models. Based on the principles identified in our review, we outline
essential components of a unified model of conscious and unconscious visual
perception. We propose that awareness refers to consolidated
visual representations, which are accessible to the entire brain and therefore
globally available. However, visual awareness not only depends
on consolidation within the visual system, but is additionally the result of a
post-sensory gating process, which is mediated by higher-level cognitive control
mechanisms. We further propose that amplification of visual representations by
attentional sensitization is not exclusive to the domain of conscious
perception, but also applies to visual stimuli, which remain unconscious.
Conscious and unconscious processing modes are highly interdependent with
influences in both directions. We therefore argue that exactly this
interdependence renders a unified model of conscious and unconscious visual
perception valuable. Computational modeling jointly with focused experimental
research could lead to a better understanding of the plethora of empirical
phenomena in consciousness research
Sensorimotor supremacy: Investigating conscious and unconscious vision by masked priming
According to the sensorimotor supremacy hypothesis, conscious perception draws on
motor action. In the present report, we will sketch two lines of potential
development in the field of masking research based on the sensorimotor supremacy
hypothesis. In the first part of the report, evidence is reviewed that masked,
invisible stimuli can affect motor responses, attention shifts, and semantic
processes. After the review of the corresponding evidence – so-called masked
priming effects – an approach based on the sensorimotor supremacy hypothesis is
detailed as to how the question of a unitary mechanism of unconscious vision can
be pursued by masked priming studies. In the second part of the report,
different models and theories of backward masking and masked priming are
reviewed. Types of models based on the sensorimotor hypothesis are discussed
that can take into account ways in which sensorimotor processes (reflected in
masked priming effects) can affect conscious vision under backward masking
conditions
Estimating the inelasticity with the information theory approach
Using the information theory approach, in both its extensive and nonextensive
versions, we estimate the inelasticity parameter of hadronic reactions
together with its distribution and energy dependence from and
data. We find that the inelasticity remains essentially constant in energy
except for a variation around , as was originally expected.Comment: 14 pages, 8 figures. Misprints correcte
Telomeric expression sites are highly conserved in trypanosoma brucei
Subtelomeric regions are often under-represented in genome sequences of eukaryotes. One of the best known examples of the use of telomere proximity for adaptive purposes are the bloodstream expression sites (BESs) of the African trypanosome Trypanosoma brucei. To enhance our understanding of BES structure and function in host adaptation and immune evasion, the BES repertoire from the Lister 427 strain of T. brucei were independently tagged and sequenced. BESs are polymorphic in size and structure but reveal a surprisingly conserved architecture in the context of extensive recombination. Very small BESs do exist and many functioning BESs do not contain the full complement of expression site associated genes (ESAGs). The consequences of duplicated or missing ESAGs, including ESAG9, a newly named ESAG12, and additional variant surface glycoprotein genes (VSGs) were evaluated by functional assays after BESs were tagged with a drug-resistance gene. Phylogenetic analysis of constituent ESAG families suggests that BESs are sequence mosaics and that extensive recombination has shaped the evolution of the BES repertoire. This work opens important perspectives in understanding the molecular mechanisms of antigenic variation, a widely used strategy for immune evasion in pathogens, and telomere biology
Scaling violations: Connections between elastic and inelastic hadron scattering in a geometrical approach
Starting from a short range expansion of the inelastic overlap function,
capable of describing quite well the elastic pp and scattering data,
we obtain extensions to the inelastic channel, through unitarity and an impact
parameter approach. Based on geometrical arguments we infer some
characteristics of the elementary hadronic process and this allows an excellent
description of the inclusive multiplicity distributions in and
collisions. With this approach we quantitatively correlate the violations of
both geometrical and KNO scaling in an analytical way. The physical picture
from both channels is that the geometrical evolution of the hadronic
constituents is principally reponsible for the energy dependence of the
physical quantities rather than the dynamical (elementary) interaction itself.Comment: 16 pages, aps-revtex, 11 figure
Excess of serotonin affects neocortical pyramidal neuron migration
The serotonin transporter (SERT) is a key molecule involved in the homeostasis of extracellular levels of serotonin and is regulated developmentally. Genetic deletion of SERT in rodents increases extracellular levels of serotonin and affects cellular processes involved in neocortical circuit assembly such as barrel cortex wiring and cortical interneuron migration. Importantly, pharmacological blockade of SERT during brain development leads to phenotypes relevant to psychiatry in rodents and to an increased risk for autism spectrum disorders in humans. Furthermore, developmental adversity interacts with genetically-driven variations of serotonin function in humans and nonhuman primates to increase the risk for a variety of stress-related phenotypes. In this study, we investigate whether an excess of serotonin affects the migration of neocortical pyramidal neurons during development. Using in utero electroporation combined with time-lapse imaging to specifically monitor pyramidal neurons during late mouse embryogenesis, we show that an excess of serotonin reversibly affects the radial migration of pyramidal neurons. We further identify that the serotonin receptor 5-HT6 is expressed in pyramidal neuron progenitors and that 5-HT6 receptor activation replicates the effects of serotonin stimulation. Finally, we show that the positioning of superficial layer pyramidal neurons is altered in vivo in SERT knockout mice. Taken together, these results indicate that a developmental excess of serotonin decreases the migration speed of cortical pyramidal neurons, affecting a fundamental step in the assembly of neural circuits. These findings support the hypothesis that developmental dysregulation of serotonin homeostasis has detrimental effects on neocortical circuit formation and contributes to increased vulnerability to psychiatric disorders
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