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851.
How the brain uses success and failure to optimize future decisions is a long-standing question in neuroscience. One computational solution involves updating the values of context-action associations in proportion to a reward prediction error. Previous evidence suggests that such computations are expressed in the striatum and, as they are cognitively impenetrable, represent an unconscious learning mechanism. Here, we formally test this by studying instrumental conditioning in a situation where we masked contextual cues, such that they were not consciously perceived. Behavioral data showed that subjects nonetheless developed a significant propensity to choose cues associated with monetary rewards relative to punishments. Functional neuroimaging revealed that during conditioning cue values and prediction errors, generated from a computational model, both correlated with activity in ventral striatum. We conclude that, even without conscious processing of contextual cues, our brain can learn their reward value and use them to provide a bias on decision making. 相似文献
852.
Benzophenone imine [M(η1-NHCPh2)(CO)nP5-n]BPh4 [M = Mn, Re; n = 2, 3; P = P(OEt)3, PPh(OEt)2, PPh2OEt, PPh3] complexes were prepared by allowing triflate M(κ1-OTf)(CO)nP5-n compounds to react with an excess of the imine. Hydride-imine [MH(η1-NHCPh2)P4]BPh4 (M = Ru, Os), triflate-imine [Os(κ1-OTf)(η1-NHCPh2)P4]BPh4 and bis(imine) [Ru(η1-NHCPh2)2P4](BPh4)2 [P = P(OEt)3] derivatives were also prepared. The complexes were characterized spectroscopically (IR, 1H, 31P, 13C NMR) and a geometry in solution was also established. Hydride-benzophenone imine [IrHCl(η1-NHCPh2)L(PPh3)2]BPh4and [IrHCl(η1-NHCPh2)L(AsPh3)2]BPh4 [L = P(OEt)3 and PPh(OEt)2] complexes were prepared by reacting hydride IrHCl2L(PPh3)2 and IrHCl2L(AsPh3)2 precursors with an excess of imine. Dihydride IrH2(η1-NHCPh2)(PPh3)3 complex was also obtained and a geometry in solution was proposed. 相似文献
853.
854.
855.
Franti?ek Balu?ka Markus Schlicht Dieter Volkmann Stefano Mancuso 《Plant signaling & behavior》2008,3(4):254-256
The plant hormone auxin is secreted in root apices via phospholipase Dζ2 (PLDζ2) activity which produces specific population of phosphatidic acid that stimulates secretion of vesicles enriched with auxin. These vesicles were reported to be localized at plant synapses which are active in auxin secretion, especially at the transition zone of the root apex. There are several implications of this vesicular secretion of auxin. In root apices, auxin emerges as plant neurotransmitter-like signal molecule which coordinates activities of adjacent cells via electric and chemical signaling. Putative quantal release of auxin after electrical stimulation, if confirmed, would be part of neuronal communication between plant cells. As auxin transport across plant synapses is tightly linked with integrated sensory perception of environment, especially of omnipresent gravity and light, this process is proposed to mediate the plant perception of environment. These neuronal features allow sessile plants to integrate multitude of sensory signals into the adaptive behavior of whole plants and the animal-like exploratory behavior of growing roots.Key words: auxin, phospholipase Dζ2, plant development, root apex, secretion, vesicles 相似文献
856.
Detailed understanding of IKs gating complexity may provide clues regarding the mechanisms of repolarization instability and the resulting arrhythmias. We developed and tested a kinetic model to interpret physiologically relevant IKs properties, including pause-dependence and modulation by β-adrenergic receptors (β-AR). IKs gating was evaluated in guinea-pig ventricular myocytes at 36°C in control and during β-AR stimulation (0.1 μmol/L isoprenaline (ISO)). We tested voltage dependence of steady-state conductance (Gss), voltage dependence of activation and deactivation time constants (τact, τdeact), and pause-dependence of τact during repetitive activations (τreact). The IKs model was developed from the Silva and Rudy formulation. Parameters were optimized on control and ISO experimental data, respectively. ISO strongly increased Gss and its voltage dependence, changed the voltage dependence of τact and τdeact, and modified the pause-dependence of τreact. A single set of model parameters reproduced all experimental data in control. Modification of only three transition rates led to a second set of parameters suitable to fit all ISO data. Channel unitary conductance and density were unchanged in the model, thus implying increased open probability as the mechanism of ISO-induced Gss enhancement. The new IKs model was applied to analyze ISO effect on repolarization rate-dependence. IKs kinetics and its β-AR modulation were entirely reproduced by a single Markov chain of transitions (for each channel monomer). Model-based analysis suggests that complete opening of IKs channels within a physiological range of potentials requires concomitant β-AR stimulation. Transient redistribution of state occupancy, in addition to direct modulation of transition rates, may underlie β-AR modulation of IKs time dependence. 相似文献
857.
Jürgen Treckmann Manfred Nagelschmidt Thomas Minor Fuat Saner Stefano Saad Andreas Paul 《Cryobiology》2009,59(1):19-23
Objectives
Especially for preservation of marginal donor organs, machine perfusion (MP) and retrograde oxygen persufflation (ROP) are alternatives to cold storage (CS). Using a porcine kidney autotransplantation model we compared metabolic and morphologic effects of CS, ROP, and MP on kidneys exposed to warm ischemia.Methods
Kidneys of 21 pigs were exposed in situ to warm ischemia for 60 min. The kidneys were randomly allocated to three experimental groups, each receiving a 4-h treatment of either cold storage, machine perfusion, or retrograde oxygen persufflation. Tissue samples were examined for malondialdehyde and histological changes. Daily blood samples were examined for creatinine levels.Results
Seven days after transplantation, the plasma creatinine levels in the CS and MP groups were still significantly elevated above the baseline values. In the ROP group, all animals exhibited nearly normal creatinine levels. Malondialdehyde, an indicator of lipidperoxidation, was dramatically increased in the machine perfused kidneys on day 7, whereas the malondialdehyde levels in the other two groups were near normal values. The MP kidneys exhibited the most striking histological changes.Conclusion
Though MP has been well introduced in organ transplantation, in our opinion, it must still be optimized and standardized. It is necessary to clarify questions such as whether there is a need for oxygenation during perfusion, the length of perfusion, the impact of pressure, and the effects of additional scavengers. The results of the present study suggest the reconsideration of the ROP-technique for the preservation of predamaged donor grafts especially of NHBD and further studies, comparing MP and ROP upon long term preservation are strongly encouraged. 相似文献858.
Manon Quiquand Jürgen Schmich Brigitte Galliot Stefano Piraino 《Developmental biology》2009,328(2):173-187
Hox and ParaHox (H/P) genes belong to evolutionary-sister clusters that arose through duplication of a ProtoHOX cluster early in animal evolution. In contrast to bilaterians, cnidarians express, beside PG1, PG2 and Gsx orthologs, numerous Hox-related genes with unclear origin. We characterized from marine hydrozoans three novel Hox-related genes expressed at medusa and polyp stages, which include a Pdx/Xlox ParaHox ortholog induced 1 day later than Gsx during embryonic development. To reconstruct H/P genes' early evolution, we performed multiple systematic comparative phylogenetic analyses, which identified derived sequences that blur the phylogenetic picture, recorded dramatically different evolutionary rates between ParaHox and Hox in cnidarians and showed the unexpected grouping of [Gsx-Pdx/Xlox-PG2-PG3] families in a single metagroup distinct from PG1. We propose a novel more parsimonious evolutionary scenario whereby H/P genes originated from a [Gsx-Pdx/Xlox-PG2-PG3]-related ProtoHox gene, the «posterior» and «anterior» H/P genes appearing secondarily. The ProtoHOX cluster would have contained the three Gsx/PG2, Pdx/PG3, Cdx/PG9 paralogs and produced through tandem duplication the primordial HOX and ParaHOX clusters in the Cnidaria-Bilateria ancestor. The stronger constraint on cnidarian ParaHox genes suggests that the primary function of pre-bilaterian H/P genes was to drive cellular evolutionary novelties such as neurogenesis rather than axis specification. 相似文献
859.
860.
Learning flexible sensori-motor mappings in a complex network 总被引:1,自引:1,他引:0
Given the complex structure of the brain, how can synaptic plasticity explain the learning and forgetting of associations
when these are continuously changing? We address this question by studying different reinforcement learning rules in a multilayer
network in order to reproduce monkey behavior in a visuomotor association task. Our model can only reproduce the learning
performance of the monkey if the synaptic modifications depend on the pre- and postsynaptic activity, and if the intrinsic
level of stochasticity is low. This favored learning rule is based on reward modulated Hebbian synaptic plasticity and shows
the interesting feature that the learning performance does not substantially degrade when adding layers to the network, even
for a complex problem. 相似文献