Andrea Antal, Rafael Polania, Carsten Schmidt-Samoa, Peter Dechent, Walter Paulus, Transcranial direct current stimulation over the primary motor cortex during fMRI, NeuroImage, Vol. 55 (2), 2011. (Journal Article)
Measurements of motor evoked potentials (MEPs) have shown that anodal and cathodal transcranial direct current stimulations (tDCS) have facilitatory or inhibitory effects on corticospinal excitability in the stimulated area of the primary motor cortex (M1). Here, we investigated the online effects of short periods of anodal and cathodal tDCS on human brain activity of healthy subjects and associated hemodynamics by concurrent blood-oxygenation-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) at 3T. Using a block design, 20s periods of tDCS at 1 mA intensity over the left M1 altered with 20s periods without tDCS. In different fMRI runs, the effect of anodal or cathodal tDCS was assessed at rest or during finger tapping. A control experiment was also performed, in which the electrodes were placed over the left and right occipito-temporo-parietal junction. Neither anodal nor cathodal tDCS over the M1 for 20s stimulation duration induced a detectable BOLD signal change. However, in comparison to a voluntary finger tapping task without stimulation, anodal tDCS during finger tapping resulted in a decrease in the BOLD response in the supplementary motor area (SMA). Cathodal stimulation did not result in significant change in BOLD response in the SMA, however, a tendency toward decreased activity could be seen. In the control experiment neither cathodal nor anodal stimulation resulted in a significant change of BOLD signal during finger tapping in any brain area including SMA, PM, and M1. These findings demonstrate that the well-known polarity-dependent shifts in corticospinal excitability that have previously been demonstrated using measurements of MEPs after M1 stimulation are not paralleled by analogous changes in regional BOLD signal. This difference implies that the BOLD signal and measurements of MEPs probe diverse physiological mechanisms. The MEP amplitude reflects changes in transsynaptic excitability of large pyramidal neurons while the BOLD signal is a measure of net synaptic activity of all cortical neurons. |
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Lope A Flórez, Katrin Gunka, Rafael Polania, Stefan Tholen, Jörg Stülke, SPABBATS: A pathway-discovery method based on Boolean satisfiability that facilitates the characterization of suppressor mutants, BMC Systems Biology, Vol. 5, 2011. (Journal Article)
BACKGROUND: Several computational methods exist to suggest rational genetic interventions that improve the productivity of industrial strains. Nonetheless, these methods are less effective to predict possible genetic responses of the strain after the intervention. This problem requires a better understanding of potential alternative metabolic and regulatory pathways able to counteract the targeted intervention.
RESULTS: Here we present SPABBATS, an algorithm based on Boolean satisfiability (SAT) that computes alternative metabolic pathways between input and output species in a reconstructed network. The pathways can be constructed iteratively in order of increasing complexity. SPABBATS allows the accumulation of intermediates in the pathways, which permits discovering pathways missed by most traditional pathway analysis methods. In addition, we provide a proof of concept experiment for the validity of the algorithm. We deleted the genes for the glutamate dehydrogenases of the Gram-positive bacterium Bacillus subtilis and isolated suppressor mutant strains able to grow on glutamate as single carbon source. Our SAT approach proposed candidate alternative pathways which were decisive to pinpoint the exact mutation of the suppressor strain.
CONCLUSIONS: SPABBATS is the first application of SAT techniques to metabolic problems. It is particularly useful for the characterization of metabolic suppressor mutants and can be used in a synthetic biology setting to design new pathways with specific input-output requirements. |
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Rafael Polania, Walter Paulus, Andrea Antal, Michael A Nitsche, Introducing graph theory to track for neuroplastic alterations in the resting human brain: a transcranial direct current stimulation study, NeuroImage, Vol. 54 (3), 2011. (Journal Article)
Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that alters cortical excitability and activity in a polarity-dependent way. Stimulation for a few minutes has been shown to induce plastic alterations of cortical excitability and to improve cognitive performance. These effects might be related to stimulation-induced alterations of functional cortical network connectivity. We aimed to investigate the impact of tDCS on cortical network function by functional connectivity and graph theoretical analysis of the BOLD fMRI spontaneous activity. fMRI resting-state datasets were acquired immediately before and after 10-min bipolar tDCS during rest, with the anode placed over the left primary motor cortex (M1) and the cathode over the contralateral frontopolar cortex. For each dataset, grey matter voxel-based synchronization matrices were calculated and thresholded to construct undirected graphs. Nodal connectivity degree and minimum path length maps were calculated and compared before and after tDCS. Nodal minimum path lengths significantly increased in the left somatomotor (SM1) cortex after anodal tDCS, which means that the number of direct functional connections from the left SM1 to topologically distant grey matter voxels significantly decreased. In contrast, functional coupling between premotor and superior parietal areas with the left SM1 significantly increased. Additionally, the nodal connectivity degree in the left posterior cingulate cortex (PCC) area as well as in the right dorsolateral prefrontal cortex (right DLPFC) significantly increased. In summary, we provide initial support that tDCS-induced neuroplastic alterations might be related to functional connectivity changes in the human brain. Additionally, we propose our approach as a powerful method to track for neuroplastic changes in the human brain. |
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Anjali Raja, Danielle Tisserand, Donald T Stuss, Anthony R McIntosh, Brian Levine, Brain activity patterns uniquely supporting visual feature integration after traumatic brain injury, Frontiers in Human Neuroscience, Vol. 5, 2011. (Journal Article)
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Markus Christen, Die Entstehung der Hirn-Computer-Analogie. Tücken und Fallstricke bei der Technisierung des Gehirns, In: Die Zukunft des menschlichen Gehirns : ethische und anthropologische Herausforderung der modernen Neurowissenschaften, Institut für Kirche und Gesellschaft, Schwerte, p. 135 - 154, 2011. (Book Chapter)
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Kevin E Staub, Essays in microeconometrics, University of Zurich, Faculty of Business, Economics and Informatics, 2011. (Dissertation)
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Jakub Steiner, Colin Stewart, Communication, timing, and common learning, Journal of Economic Theory, Vol. 146 (1), 2011. (Journal Article)
We study the effect of stochastically delayed communication on common knowledge acquisition (common learning). If messages do not report dispatch times, communication prevents common learning under general conditions even if common knowledge is acquired without communication. If messages report dispatch times, communication can destroy common learning under more restrictive conditions. The failure of common learning in the two cases is based on different infection arguments. Communication can destroy common learning even if it ends in finite time, or if agents communicate all of their information. We also identify conditions under which common learning is preserved in the presence of communication. |
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P Mahler, Sich im Erfolg des Geleisteten suhlen, In: NZZ, 304, p. 55, 30 December 2010. (Newspaper Article)
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P Mahler, Nicht nur der Vorgesetzte führt, In: Neue Zürcher Zeitung, 299, p. 59, 23 December 2010. (Newspaper Article)
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Bruno Frey, Glückliche Menschen leben besser und länger, In: Neue Zürcher Zeitung, 298, p. 21, 22 December 2010. (Newspaper Article)
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Helmut Max Dietl, Zur Ökonomie des Schenkens, In: Neue Zürcher Zeitung, 294, p. 23, 17 December 2010. (Newspaper Article)
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Jean Daunizeau, H E M den Ouden, M Pessiglione, S J Kiebel, Klaas Enno Stephan, K J Friston, Observing the observer (I): Meta-bayesian models of learning and decision-making, PLoS ONE, Vol. 5 (12), 2010. (Journal Article)
In this paper, we present a generic approach that can be used to infer how subjects make optimal decisions under uncertainty. This approach induces a distinction between a subject’s perceptual model, which underlies the representation of a hidden "state of affairs" and a response model, which predicts the ensuing behavioural (or neurophysiological) responses to those inputs. We start with the premise that subjects continuously update a probabilistic representation of the causes of their sensory inputs to optimise their behaviour. In addition, subjects have preferences or goals that guide decisions about actions given the above uncertain representation of these hidden causes or state of affairs. From a Bayesian decision theoretic perspective, uncertain representations are so-called "posterior" beliefs, which are influenced by subjective "prior" beliefs. Preferences and goals are encoded through a "loss" (or "utility") function, which measures the cost incurred by making any admissible decision for any given (hidden) state of affair. By assuming that subjects make optimal decisions on the basis of updated (posterior) beliefs and utility (loss) functions, one can evaluate the likelihood of observed behaviour. Critically, this enables one to "observe the observer", i.e. identify (context- or subject-dependent) prior beliefs and utility-functions using psychophysical or neurophysiological measures. In this paper, we describe the main theoretical components of this meta-Bayesian approach (i.e. a Bayesian treatment of Bayesian decision theoretic predictions). In a companion paper (‘Observing the observer (II): deciding when to decide’), we describe a concrete implementation of it and demonstrate its utility by applying it to simulated and real reaction time data from an associative learning task. |
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Jean Daunizeau, H E M den Ouden, M Pessiglione, S J Kiebel, K J Friston, Klaas Enno Stephan, Observing the observer (II): Deciding when to decide, PLoS ONE, Vol. 5 (12), 2010. (Journal Article)
In a companion paper [1], we have presented a generic approach for inferring how subjects make optimal decisions under uncertainty. From a Bayesian decision theoretic perspective, uncertain representations correspond to “posterior” beliefs, which result from integrating (sensory) information with subjective “prior” beliefs. Preferences and goals are encoded through a “loss” (or “utility”) function, which measures the cost incurred by making any admissible decision for any given (hidden or unknown) state of the world. By assuming that subjects make optimal decisions on the basis of updated (posterior) beliefs and utility (loss) functions, one can evaluate the likelihood of observed behaviour. In this paper, we describe a concrete implementation of this meta-Bayesian approach (i.e. a Bayesian treatment of Bayesian decision theoretic predictions) and demonstrate its utility by applying it to both simulated and empirical reaction time data from an associative learning task. Here, inter-trial variability in reaction times is modelled as reflecting the dynamics of the subjects' internal recognition process, i.e. the updating of representations (posterior densities) of hidden states over trials while subjects learn probabilistic audio-visual associations. We use this paradigm to demonstrate that our meta-Bayesian framework allows for (i) probabilistic inference on the dynamics of the subject's representation of environmental states, and for (ii) model selection to disambiguate between alternative preferences (loss functions) human subjects could employ when dealing with trade-offs, such as between speed and accuracy. Finally, we illustrate how our approach can be used to quantify subjective beliefs and preferences that underlie inter-individual differences in behaviour. |
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Xuan Yang, Daning Hu, Robert Davison, How Microblogging Networks Affect OSS Success, In: International Conference on Information Systems (ICIS ‘10), 2010. (Conference or Workshop Paper published in Proceedings)
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Daning Hu, J Leon Zhao, Zhimin Hua, Ranking Systemic Risks in Bank Networks, In: International Conference on Information Systems (ICIS) 2010, Association for Information Systems; AIS Electronic Library (AISeL), St. Louis, USA, 2010-12-12. (Conference or Workshop Paper published in Proceedings)
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Susanne Schmidt-Rauch, R Schär, Gerhard Schwabe, From telesales to tele-advisory services in travel agencies, In: International Conference on Information Systems (ICIS) 2010, 2010-12-12. (Conference or Workshop Paper published in Proceedings)
Travel agency call centers are intended to complement advisory services of the bricks-and-mortar travel agencies by providing remote advisory services. Currently, they are ill-prepared for giving such advisory services due to their limitations in several areas of their work practice. This article presents the organizational as well as information and communication-related issues in work practice that need to be addressed preparing call centers to sufficiently give advice at the phone using an Internet connection. Resulting design requirements concern trust, information quality, joint problem-solving, and user satisfaction. In order to test the derived design requirements, the TeleSmarttravel system was implemented and evaluated in a preliminary use at a real travel agency call center. Results indicate that a visually enhanced, collaboratively used advisory support system can beneficially influence the advisory for both the agent and the customer and therefore opens new opportunities for an innovative multi-channel advisory approach. |
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Anja Feierabend, Eifersucht am Arbeitsplatz, In: Neue Zürcher Zeitung, 289, p. 83, 11 December 2010. (Newspaper Article)
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Christian Vögtlin, Ina Maria Kaufmann, Neuroscience and Leadership Research: Fact or Fancy?, In: Neurosociety… What is it with the brain these days?. 2010. (Conference Presentation)
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Hugo Gravato Marques, Michael Jäntsch, Steffen Wittmeier, Cristiano Alessandro, Alan Diamond, Massimiliano Lungarella, Rob Knight, Owen Holland, ECCE1: the first of a series of anthropomimetic musculoskelal upper torsos., In: International Conference on Humanoid Robotics. 2010. (Conference Presentation)
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Bruno Frey, Ein Buch fürs Leben. Alexandre Dumas «Drei Musketiere», In: Tages Anzeiger Magazin, 48, p. 42, 4 December 2010. (Newspaper Article)
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