17,016 research outputs found
A Neuro-computational Account of Arbitration between Choice Imitation and Goal Emulation during Human Observational Learning
When individuals learn from observing the behavior of others, they deploy at least two distinct strategies. Choice imitation involves repeating other agents’ previous actions, whereas emulation proceeds from inferring their goals and intentions. Despite the prevalence of observational learning in humans and other social animals, a fundamental question remains unaddressed: how does the brain decide which strategy to use in a given situation? In two fMRI studies (the second a pre-registered replication of the first), we identify a neuro-computational mechanism underlying arbitration between choice imitation and goal emulation. Computational modeling, combined with a behavioral task that dissociated the two strategies, revealed that control over behavior was adaptively and dynamically weighted toward the most reliable strategy. Emulation reliability, the model’s arbitration signal, was represented in the ventrolateral prefrontal cortex, temporoparietal junction, and rostral cingulate cortex. Our replicated findings illuminate the computations by which the brain decides to imitate or emulate others
Joint interpretation of AER/FGF and ZPA/SHH over time and space underlies hairy2 expression in the chick limb
Embryo development requires precise orchestration of cell proliferation and differentiation in both time and space. A molecular clock operating through gene expression oscillations was first described in the presomitic mesoderm (PSM) underlying periodic somite formation. Cycles of HES gene expression have been further identified in other progenitor cells, including the chick distal limb mesenchyme, embryonic neural progenitors and both mesenchymal and embryonic stem cells. In the limb, hairy2 is expressed in the distal mesenchyme, adjacent to the FGF source (AER) and along the ZPA-derived SHH gradient, the two major regulators of limb development. Here we report that hairy2 expression depends on joint AER/FGF and ZPA/SHH signaling. FGF plays an instructive role on hairy2, mediated by Erk and Akt pathway activation, while SHH acts by creating a permissive state defined by Gli3-A/Gli3-R>1. Moreover, we show that AER/FGF and ZPA/SHH present distinct temporal and spatial signaling properties in the distal limb mesenchyme: SHH acts at a long-term, long-range on hairy2, while FGF has a shortterm, short-range action. Our work establishes limb hairy2 expression as an output of integrated FGF and SHH signaling in time and space, providing novel clues for understanding the regulatory mechanisms underlying HES oscillations in multiple systems, including embryonic stem cell pluripotency. (C) 2012. Published by The Company of Biologists Ltd.FCT, Portugal [SFRH/BD/33176/2007]; Ciencia2007 Program Contract (Portuguese Government); IBB/CBME, LA; FCT, Portugal (National and FEDER COMPETE Program funds) [PTDC/SAU-OBD/099758/2008, PTDC/SAU-OBD/105111/2008]info:eu-repo/semantics/publishedVersio
Tribal Sovereign Authority and Self-Regulation of Health Care Services: The Legal Framework and the Swinomish Tribe’s Dental Health Program
Migration and the formation of systems of hot super-Earths and Neptunes
The existence of extrasolar planets with short orbital periods suggests that
planetary migration induced by tidal interaction with the protoplanetary disk
is important. Cores and terrestrial planets may undergo migration as they form.
In this paper we investigate the evolution of a population of cores with
initial masses in the range 0.1-1 earth mass embedded in a disk. Mutual
interactions lead to orbit crossing and mergers, so that the cores grow during
their evolution. Interaction with the disk leads to orbital migration, which
results in the cores capturing each other in mean motion resonances. As the
cores migrate inside the disk inner edge, scatterings and mergers of planets on
unstable orbits together with orbital circularization causes strict
commensurability to be lost. Near commensurability however is usually
maintained. All the simulations end with a population of typically between two
and five planets, with masses depending on the initial mass. These results
indicate that if hot super-Earths or Neptunes form by mergers of inwardly
migrating cores, then such planets are most likely not isolated. We would
expect to always find at least one, more likely a few, companions on close and
often near-commensurable orbits. To test this hypothesis, it would be of
interest to look for planets of a few to about 10 earth masses in systems where
hot super-Earths or Neptunes have already been found.Comment: 29 pages, to be published in Ap
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