335 research outputs found
Electrophysiological Signatures of Fear Conditioning: From Methodological Considerations to Catecholaminergic Mechanisms and Translational Perspectives
Fear conditioning describes a learning mechanism during which a specific stimulus gets associated with an aversive event (i.e., an unconditioned stimulus; US). Thereby, this initially neutral or arbitrary stimulus becomes a so-called âconditionedâ stimulus (CS), which elicits a conditioned threat response. Fear extinction refers to the decrease in conditioned threat responses as soon as the CS is repeatedly presented in the absence of the US. While fear conditioning is an important learning model for understanding the etiology and maintenance of anxiety and fear-related disorders, extinction learning is considered to reflect the most important learning process of exposure therapy. Neurophysiological signatures of fear conditioning have been widely studied in rodents, leading to the development of groundbreaking neurobiological models, including brain regions such as the amygdala, insula, and prefrontal areas. These models aim to explain neural mechanisms of threat processing, with the ultimate goal to improve treatment strategies for pathological fear. Recording intracranial electrical activity of single units in animals offers the opportunity to uncover neural processes involved in threat processing with excellent spatial and temporal resolution. A large body of functional magnetic resonance imaging (fMRI) studies have helped to translate this knowledge about the anatomy of fear conditioning into the human realm. fMRI is an imaging technique with a high spatial resolution that is well suited to study slower brain processes. However, the temporal resolution of fMRI is relatively poor. By contrast, electroencephalography (EEG) is a neuroscientific method to capture fast and transient cortical processes. While EEG offers promising opportunities to unravel the speed of neural threat processing, it also provides the possibility to study oscillatory brain activity (e.g., prefrontal theta oscillations). The present thesis contains six research manuscripts, describing fear conditioning studies that mainly applied EEG methods in combination with other central (fMRI) and peripheral (skin conductance, heart rate, and fear-potentiated startle) measures. A special focus of this thesis lies in methodological considerations for EEG fear conditioning research. In addition, catecholaminergic mechanisms are studied, with the ultimate goal of opening up new translational perspectives. Taken together, the present thesis addresses several methodological challenges for neuroscientific (in particular, EEG) fear conditioning research (e.g., appropriate US types and experimental designs, signal-to-noise ratio, simultaneous EEG-fMRI). Furthermore, this thesis gives critical insight into catecholaminergic (noradrenaline and dopamine) mechanisms. A variety of neuroscientific methods (e.g., EEG, fMRI, peripheral physiology, pharmacological manipulation, genetic associations) have been combined, an approach that allowed us (a) to translate knowledge from animal studies to human research, and (b) to stimulate novel clinical directions
Critical Decay at Higher-Order Glass-Transition Singularities
Within the mode-coupling theory for the evolution of structural relaxation in
glass-forming systems, it is shown that the correlation functions for density
fluctuations for states at A_3- and A_4-glass-transition singularities can be
presented as an asymptotic series in increasing inverse powers of the logarithm
of the time t: , where
with p_n denoting some polynomial and x=ln (t/t_0). The results are
demonstrated for schematic models describing the system by solely one or two
correlators and also for a colloid model with a square-well-interaction
potential.Comment: 26 pages, 7 figures, Proceedings of "Structural Arrest Transitions in
Colloidal Systems with Short-Range Attractions", Messina, Italy, December
2003 (submitted
EEG Microstates in Social and Affective Neuroscience.
Social interactions require both the rapid processing of multifaceted socio-affective signals (e.g., eye gaze, facial expressions, gestures) and their integration with evaluations, social knowledge, and expectations. Researchers interested in understanding complex social cognition and behavior face a "black box" problem: What are the underlying mental processes rapidly occurring between perception and action and why are there such vast individual differences? In this review, we promote electroencephalography (EEG) microstates as a powerful tool for both examining socio-affective states (e.g., processing whether someone is in need in a given situation) and identifying the sources of heterogeneity in socio-affective traits (e.g., general willingness to help others). EEG microstates are identified by analyzing scalp field maps (i.e., the distribution of the electrical field on the scalp) over time. This data-driven, reference-independent approach allows for identifying, timing, sequencing, and quantifying the activation of large-scale brain networks relevant to our socio-affective mind. In light of these benefits, EEG microstates should become an indispensable part of the methodological toolkit of laboratories working in the field of social and affective neuroscience
Detection of Solar-like Oscillations in the G7 Giant Star xi Hya
We report the firm discovery of solar-like oscillations in a giant star. We
monitored the star xi Hya (G7III) continuously during one month with the
CORALIE spectrograph attached to the 1.2m Swiss Euler telescope. The 433
high-precision radial-velocity measurements clearly reveal multiple oscillation
frequencies in the range 50 - 130 uHz, corresponding to periods between 2.0 and
5.5 hours. The amplitudes of the strongest modes are slightly smaller than 2
m/s. Current model calculations are compatible with the detected modes.Comment: 4 pages, 4 figures, accepted for publication as a letter in A&
Dynamic Glass Transition in Two Dimensions
The question about the existence of a structural glass transition in two
dimensions is studied using mode coupling theory (MCT). We determine the
explicit d-dependence of the memory functional of mode coupling for
one-component systems. Applied to two dimensions we solve the MCT equations
numerically for monodisperse hard discs. A dynamic glass transition is found at
a critical packing fraction phi_c^{d=2} = 0.697 which is above phi_c^{d=3} =
0.516 by about 35%. phi^d_c scales approximately with phi^d_{\rm rcp} the value
for random close packing, at least for d=2, 3. Quantities characterizing the
local, cooperative 'cage motion' do not differ much for d=2 and d=3, and we
e.g. find the Lindemann criterion for the localization length at the glass
transition. The final relaxation obeys the superposition principle, collapsing
remarkably well onto a Kohlrausch law. The d=2 MCT results are in qualitative
agreement with existing results from MC and MD simulations. The mean squared
displacements measured experimentally for a quasi-two-dimensional binary system
of dipolar hard spheres can be described satisfactorily by MCT for monodisperse
hard discs over four decades in time provided the experimental control
parameter Gamma (which measures the strength of dipolar interactions) and the
packing fraction phi are properly related to each other.Comment: 14 pages, 15 figure
Higher-order glass-transition singularities in systems with short-ranged attractive potentials
Within the mode-coupling theory for the evolution of structural relaxation,
the A_4 glass-transition singularities are identified for systems of particles
interacting with a hard-sphere repulsion complemented by different short-ranged
potentials: Baxter's singular potential regularized by a large-wave-vector
cutoff, a model for the Asakura-Oosawa depletion attraction, a triangular
potential, a Yukawa attraction, and a square-well potential. The regular
potentials yield critical packing fractions, critical Debye-Waller factors and
critical amplitudes very close to each other. The elastic moduli and the
particle's localization lengths for corresponding states of the Yukawa system
and the square-well system may differ by up to 20% and 10%, respectively.Comment: 12 pages, 5 figures, J. Phys. Cond. Matt. to be publishe
Numerical study of the glass-glass transition in short-ranged attractive colloids
We report extensive numerical simulations in the {\it glass} region for a
simple model of short-ranged attractive colloids, the square well model. We
investigate the behavior of the density autocorrelation function and of the
static structure factor in the region of temperatures and packing fractions
where a glass-glass transition is expected according to theoretical
predictions. We strengthen our observations by studying both waiting time and
history dependence of the numerical results. We provide evidence supporting the
possibility that activated bond-breaking processes destabilize the attractive
glass, preventing the full observation of a sharp glass-glass kinetic
transition.Comment: 15 pages, 9 figures; Proceedings of "Structural Arrest Transitions in
Colloidal Systems with Short-Range Attractions", Messina, Italy, December
2003 (submitted to J. Phys.: Condens. Matt.
Dynamics in Colloidal Liquids near a Crossing of Glass- and Gel-Transition Lines
Within the mode-coupling theory for ideal glass-transitions, the mean-squared
displacement and the correlation function for density fluctuations are
evaluated for a colloidal liquid of particles interacting with a square-well
potential for states near the crossing of the line for transitions to a gel
with the line for transitions to a glass. It is demonstrated how the dynamics
is ruled by the interplay of the mechanisms of arrest due to hard-core
repulsion and due to attraction-induced bond formation as well as by a nearby
higher-order glass-transition singularity. Application of the universal
relaxation laws for the slow dynamics near glass-transition singularities
explains the qualitative features of the calculated time dependence of the
mean-squared displacement, which are in accord with the findings obtained in
molecular-dynamics simulation studies by Zaccarelli et. al [Phys. Rev. E 66,
041402 (2002)]. Correlation functions found by photon-correlation spectroscopy
in a micellar system by Mallamace et. al [Phys. Rev. Lett. 84, 5431 2000)] can
be interpreted qualitatively as a crossover from gel to glass dynamics.Comment: 13 pages, 12 figure
A Revised Framework for the Investigation of Expectation Update Versus Maintenance in the Context of Expectation Violations: The ViolEx 2.0 Model
Expectations are probabilistic beliefs about the future that shape and influence our
perception, affect, cognition, and behavior in many contexts. This makes expectations
a highly relevant concept across basic and applied psychological disciplines. When
expectations are confirmed or violated, individuals can respond by either updating or
maintaining their prior expectations in light of the new evidence. Moreover, proactive
and reactive behavior can change the probability with which individuals encounter
expectation confirmations or violations. The investigation of predictors and mechanisms
underlying expectation update and maintenance has been approached from many
research perspectives. However, in many instances there has been little exchange
between different research fields. To further advance research on expectations and
expectation violations, collaborative efforts across different disciplines in psychology,
cognitive (neuro)science, and other life sciences are warranted. For fostering and
facilitating such efforts, we introduce the ViolEx 2.0 model, a revised framework
for interdisciplinary research on cognitive and behavioral mechanisms of expectation
update and maintenance in the context of expectation violations. To support different
goals and stages in interdisciplinary exchange, the ViolEx 2.0 model features three
model levels with varying degrees of specificity in order to address questions about
the research synopsis, central concepts, or functional processes and relationships,
respectively. The framework can be applied to different research fields and has high
potential for guiding collaborative research efforts in expectation research
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