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Learning Contextual Reward Expectations for Value Adaptation
Substantial evidence indicates that subjective value is adapted to the statistics of reward expected within a given temporal context. However, how these contextual expectations are learned is poorly understood. To examine such learning, we exploited a recent observation that participants performing a gambling task adjust their preferences as a function of context. We show that, in the absence of contextual cues providing reward information, an average reward expectation was learned from recent past experience. Learning dependent on contextual cues emerged when two contexts alternated at a fast rate, whereas both cue-independent and cue-dependent forms of learning were apparent when two contexts alternated at a slower rate. Motivated by these behavioral findings, we reanalyzed a previous fMRI data set to probe the neural substrates of learning contextual reward expectations. We observed a form of reward prediction error related to average reward such that, at option presentation, activity in ventral tegmental area/substantia nigra and ventral striatum correlated positively and negatively, respectively, with the actual and predicted value of options. Moreover, an inverse correlation between activity in ventral tegmental area/substantia nigra (but not striatum) and predicted option value was greater in participants showing enhanced choice adaptation to context. The findings help understanding the mechanisms underlying learning of contextual reward expectation
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The Dopaminergic Midbrain Mediates an Effect of Average Reward on Pavlovian Vigor
Dopamine plays a key role in motivation. Phasic dopamine response reflects a reinforcement prediction error (RPE), whereas tonic dopamine activity is postulated to represent an average reward that mediates motivational vigor. However, it has been hard to find evidence concerning the neural encoding of average reward that is uncorrupted by influences of RPEs. We circumvented this difficulty in a novel visual search task where we measured participants' button pressing vigor in a context where information (underlying an RPE) about future average reward was provided well before the average reward itself. Despite no instrumental consequence, participants' pressing force increased for greater current average reward, consistent with a form of Pavlovian effect on motivational vigor. We recorded participants' brain activity during task performance with fMRI. Greater average reward was associated with enhanced activity in dopaminergic midbrain to a degree that correlated with the relationship between average reward and pressing vigor. Interestingly, an opposite pattern was observed in subgenual cingulate cortex, a region implicated in negative mood and motivational inhibition. These findings highlight a crucial role for dopaminergic midbrain in representing aspects of average reward and motivational vigor
Spin Two Glueball Mass and Glueball Regge Trajectory from Supergravity
We calculate the mass of the lowest lying spin two glueball in N=1 super
Yang-Mills from the dual Klebanov-Strassler background. We show that the Regge
trajectory obtained is linear; the 0++, 1-- and 2++ states lie on a line of
slope 0.23 -measured in units of the conifold deformation. We also compare mass
ratios with lattice data and find agreement within one standard deviation.Comment: 17 pages, 2 figure
Matching Points with Things
Given an ordered set of points and an ordered set of geometric objects in the plane, we are interested in finding a non-crossing matching between point-object pairs. We show that when the objects we match the points to are finite point sets, the problem is NP-complete in general, and polynomial when the objects are on a line or when their number is at most 2. When the objects are line segments, we show that the problem is NP-complete in general, and polynomial when the segments form a convex polygon or are all on a line. Finally, for objects that are straight lines, we show that the problem of finding a min-max non-crossing matching is NP-complete
\pi N scattering in relativistic baryon chiral perturbation theory revisited
We have analyzed pion-nucleon scattering using the manifestly relativistic
covariant framework of Infrared Regularization up to {\cal O}(q^3) in the
chiral expansion, where q is a generic small momentum. We describe the
low-energy phase shifts with a similar quality as previously achieved with
Heavy Baryon Chiral Perturbation Theory, \sqrt{s}\lesssim1.14 GeV. New values
are provided for the {\cal O}(q^2) and {\cal O}(q^3) low-energy constants,
which are compared with previous determinations. This is also the case for the
scattering lengths and volumes. Finally, we have unitarized the previous
amplitudes and as a result the energy range where data are reproduced increases
significantly.Comment: 26 pages, 5 figures, 5 table
Balancing Minimum Spanning and Shortest Path Trees
This paper give a simple linear-time algorithm that, given a weighted
digraph, finds a spanning tree that simultaneously approximates a shortest-path
tree and a minimum spanning tree. The algorithm provides a continuous
trade-off: given the two trees and epsilon > 0, the algorithm returns a
spanning tree in which the distance between any vertex and the root of the
shortest-path tree is at most 1+epsilon times the shortest-path distance, and
yet the total weight of the tree is at most 1+2/epsilon times the weight of a
minimum spanning tree. This is the best tradeoff possible. The paper also
describes a fast parallel implementation.Comment: conference version: ACM-SIAM Symposium on Discrete Algorithms (1993
Resonances from meson-meson scattering in U(3) CHPT
In this work, the complete one loop calculation of meson-meson scattering
amplitudes within U(3)\otimes U(3) chiral perturbation theory with explicit
resonance states is carried out for the first time. Partial waves are
unitarized from the perturbative calculation employing a non-perturbative
approach based on the N/D method. Once experimental data are reproduced in a
satisfactory way we then study the resonance properties, such as the pole
positions, corresponding residues and their N_C behaviors. The resulting N_C
dependence is the first one in the literature that takes into account the fact
that the \eta_1 becomes the ninth Goldstone boson in the chiral limit for large
N_C. Within this scheme the vector resonances studied, \rho(770), K^*(892) and
\phi(1020), follow an N_C trajectory in agreement with their standard \bar{q}q
interpretation. The scalars f_0(1370), a_0(1450) and K^*(1430) also have for
large N_C a \bar{q}q pole position trajectory and all of them tend to a bare
octet of scalar resonances around 1.4 GeV. The f_0(980) tends asymptotically to
the bare pole position of a singlet scalar resonance around 1 GeV. The \sigma,
\kappa and a_0(980) scalar resonances have a very different N_C behavior. The
case of the \sigma resonance is analyzed with special detail.Comment: 50 pages, 15 figures, 1 table. Enlarged version with more detail
comparisons with previous results in the literature. To match with accepted
version for publicatio
Pain assessment and pain treatment for community-dwelling people with dementia: A systematic review and narrative synthesis.
OBJECTIVES:
To describe the current literature on pain assessment and pain treatment for community-dwelling people with dementia.
METHOD:
A comprehensive systematic search of the literature with narrative synthesis was conducted. Eight major bibliographic databases were searched in October 2018. Titles, abstracts, and full-text articles were sequentially screened. Standardised data extraction and quality appraisal exercises were conducted.
RESULTS:
32 studies were included in the review, 11 reporting findings on pain assessment tools or methods, and 27 reporting findings on treatments for pain. In regard to pain assessment, a large proportion of people with moderate to severe dementia were unable to complete a self-report pain instrument. Pain was more commonly reported by informal caregivers than the person with dementia themselves. Limited evidence was available for pain focused behavioural observation assessment. In regard to pain treatment, paracetamol use was more common in community-dwelling people with dementia compared to people without dementia. However, non-steroidal anti-inflammatory drugs (NSAIDs) were used less. For stronger analgesics, community-dwelling people with dementia were more likely to receive strong opioids (e.g. fentanyl) than people without dementia.
CONCLUSION:
This review identifies a dearth of high quality studies exploring pain assessment and/or treatment for community-dwelling people with dementia, not least into non-pharmacological interventions. The consequences of this lack of evidence, given the current and projected prevalence of the disease, are very serious and require urgent redress. In the meantime, clinicians should adopt a patient and caregiver centred, multi-dimensional, longitudinal approach to pain assessment and pain treatment for this population
Casimir force acting on magnetodielectric bodies embedded in media
Within the framework of macroscopic quantum electrodynamics, general
expressions for the Casimir force acting on linearly and causally responding
magnetodielectric bodies that can be embedded in another linear and causal
magnetodielectric medium are derived. Consistency with microscopic
harmonic-oscillator models of the matter is shown. The theory is applied to
planar structures and proper generalizations of Casimir's and Lifshitz-type
formulas are given.Comment: 15 pages, 2 figures; minor additions and corrections, to appear in
PR
Trapping cold atoms near carbon nanotubes: thermal spin flips and Casimir-Polder potential
We investigate the possibility to trap ultracold atoms near the outside of a
metallic carbon nanotube (CN) which we imagine to use as a miniaturized
current-carrying wire. We calculate atomic spin flip lifetimes and compare the
strength of the Casimir-Polder potential with the magnetic trapping potential.
Our analysis indicates that the Casimir-Polder force is the dominant loss
mechanism and we compute the minimum distance to the carbon nanotube at which
an atom can be trapped.Comment: 8 pages, 3 figure
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