Martin Waldburger, Updated Market and Regulation Report (D2.1.3), Version: 1, 2007. (Technical Report)
|
|
David Hausheer, Isabelle Chrisment (Eds.), AIMS 2007 Tutorial Handbook, Oslo University College, Norway, 2007. (Book/Research Monograph)
|
|
Burkhard Stiller, Thomas Bocek, Cristian Morariu, Peter Racz, Gregor Schaffrath, Martin Waldburger (Eds.), Mobile Systems II, Version: 1, 2007. (Technical Report)
|
|
Peter Racz, Gregor Schaffrath, Jan Gerke, Burkhard Stiller, Thomas Walter, Diameter-based Accounting Management for Multiple Mobile Network Operators and its Implementation (DAMMO II): Testing and Evaluation Documentation, Version: 1, 2007. (Technical Report)
|
|
Peter Racz, Gregor Schaffrath, Jan Gerke, Burkhard Stiller, Thomas Walter, Diameter-based Accounting Management for Multiple Mobile Network Operators and its Implementation (DAMMO II): Implementation Documentation, Version: 1, 2007. (Technical Report)
|
|
Burkhard Stiller, Pascal Kurtansky, Verrechnung von IP-Dienstleistungen im Internet Bestehende Ansätze und die Herausforderungen an zukünftige IP-Netze, Bulletin SEV/VSE, Vol. 2007 (3), 2007. (Journal Article)
Dienstleistungen basierend auf IP werden im Internet mit zunehmender Vielfalt angeboten. Das wachsende Dienstangebot wird durch die verstärkte Verbreitung von IP getragen und in einigen Jahren zu All-IP führen. Aus dieser All-IP-Perspektive ergeben sich an Verrechnungssysteme von IP-Dienstleistungen zusätzliche Anforderungen. Eine dieser ist die Unterstützung der in den mobilen Telekommunikationsnetzen weit verbreiteten Prepaid-Verrechnung. |
|
Torsten Braun, Georg Carle, Burkhard Stiller, KiVS 2007 - Industriebeiträge, Kurzbeiträge, Workshops, VDE Verlag Berlin, Germany, Bern, Switzerland, 2007. (Book/Research Monograph)
|
|
Torsten Braun, Georg Carle, Burkhard Stiller, Kommunikation in Verteilten Systemen (KiVS 2007), Springer, Heidelberg, Germany, Bern, Switzerland, 2007. (Book/Research Monograph)
|
|
Martin Waldburger, Cristian Morariu, Peter Racz, Jürgen Jähnert, Stefan Wesner, Burkhard Stiller, Grids in a Mobile World: Akogrimo?s Network and Business Views, Praxis der Informationsverarbeitung und Kommunikation (PIK), Vol. 30 (1), 2007. (Journal Article)
|
|
David Hausheer, Burkhard Stiller, PeerMart: Decentralized Auctions for Bandwidth Trading on Demand, ERCIM News (68), 2007. (Journal Article)
|
|
Philippe Tobler, T Kalenscher, Awfully afraid? Dissociating decision- from motor- and sensory-related brain activation during perceptual choices, Journal of Neuroscience, Vol. 27 (23), 2007. (Journal Article)
|
|
T Kalenscher, Philippe Tobler, Comparing risky and inter-temporal decisions: Views from psychology, ecology and microeconomics, In: Psychology of decision making in economics, business and finance, Nova Publishers, Hauppage, NY, p. 111 - 135, 2007. (Book Chapter)
When making decisions between different options, we often consider two basic properties of these options, how risky they are and when they will occur. For example, we may choose to gamble or to wait for a larger reward. Decisions under risk refer to decisions among known probabilistic options, inter-temporal decisions refer to choices between options that will be realized at known future timepoints.
Risky and inter-temporal decisions have been captured theoretically primarily by Ecology and Microeconomics but findings from Behavioral Economics, Psychology and Neuroscience often contradicted theoretical predictions. As a consequence, a wealth of more descriptive models has emerged to explain the findings. A subset of these models has stressed the similarities between risky and inter-temporal decisions. In this chapter we review both core theoretical approaches and empirical findings. We discuss possible explanations for discrepancies and identify key behavioral experiments. |
|
Philippe Tobler, P C Fletcher, E T Bullmore, W Schultz, Learning-related human brain activations reflecting individual finances, Neuron, Vol. 54 (1), 2007. (Journal Article)
A basic tenet of microeconomics suggests that the subjective value of financial gains decreases with increasing assets of individuals ("marginal utility"). Using concepts from learning theory and microeconomics, we assessed the capacity of financial rewards to elicit behavioral and neuronal changes during reward-predictive learning in participants with different financial backgrounds. Behavioral learning speed during both acquisition and extinction correlated negatively with the assets of the participants, irrespective of education and age. Correspondingly, response changes in midbrain and striatum measured with functional magnetic resonance imaging were slower during both acquisition and extinction with increasing assets and income of the participants. By contrast, asymptotic magnitudes of behavioral and neuronal responses after learning were unrelated to personal finances. The inverse relationship of behavioral and neuronal learning speed with personal finances is compatible with the general concept of decreasing marginal utility with increasing wealth. |
|
M J Grol, J Majdandzić, Klaas Enno Stephan, L Verhagen, H C Dijkerman, H Bekkering, F A J Verstraten, I Toni, Parieto-frontal connectivity during visually guided grasping, Journal of Neuroscience, Vol. 27 (44), 2007. (Journal Article)
Grasping an object requires processing visuospatial information about the extrinsic features (spatial location) and intrinsic features (size, shape, orientation) of the object. Accordingly, manual prehension has been subdivided into a reach component, guiding the hand toward the object on the basis of its extrinsic features, and a grasp component, preshaping the fingers around the center of mass of the object on the basis of its intrinsic features. In neural terms, this distinction has been linked to a dedicated dorsomedial "reaching" circuit and a dorsolateral "grasping" circuit that process extrinsic and intrinsic features, linking occipital areas via parietal regions with the dorsal and ventral premotor cortex, respectively. We have tested an alternative possibility, namely that the relative contribution of the two circuits is related to the degree of on-line control required by the prehension movement. We used dynamic causal modeling of functional magnetic resonance imaging time series to assess how parieto-frontal connectivity is modulated by planning and executing prehension movements toward objects of different size and width. This experimental manipulation evoked different movements, with different planning and execution phases for the different objects. Crucially, grasping large objects increased inter-regional couplings within the dorsomedial circuit, whereas grasping small objects increased the effective connectivity of a mainly dorsolateral circuit, with a degree of overlap between these circuits. These results argue against the presence of dedicated cerebral circuits for reaching and grasping, suggesting that the contributions of the dorsolateral and the dorsomedial circuits are a function of the degree of on-line control required by the movement. |
|
Christian Ruff, A Kristjánsson, J Driver, Readout from iconic memory and selective spatial attention involve similar neural processes, Psychological Science, Vol. 18 (10), 2007. (Journal Article)
Iconic memory and spatial attention are often considered separately, but they may have functional similarities. Here we provide functional magnetic resonance imaging evidence for some common underlying neural effects. Subjects judged three visual stimuli in one hemifield of a bilateral array comprising six stimuli. The relevant hemifield for partial report was indicated by an auditory cue, administered either before the visual array (precue, spatial attention) or shortly after the array (postcue, iconic memory). Pre- and postcues led to similar activity modulations in lateral occipital cortex contralateral to the cued side. This finding indicates that readout from iconic memory can have some neural effects similar to those of spatial attention. We also found common bilateral activation of a fronto-parietal network for postcue and precue trials. These neuroimaging data suggest that some common neural mechanisms underlie selective spatial attention and readout from iconic memory. Some differences were also found; compared with precues, postcues led to higher activity in the right middle frontal gyrus. |
|
Philippe Tobler, J P O'Doherty, R J Dolan, W Schultz, Reward value coding distinct from risk attitude-related uncertainty coding in human reward systems, Journal of Neurophysiology, Vol. 97 (2), 2007. (Journal Article)
When deciding between different options, individuals are guided by the expected (mean) value of the different outcomes and by the associated degrees of uncertainty. We used functional magnetic resonance imaging to identify brain activations coding the key decision parameters of expected value (magnitude and probability) separately from uncertainty (statistical variance) of monetary rewards. Participants discriminated behaviorally between stimuli associated with different expected values and uncertainty. Stimuli associated with higher expected values elicited monotonically increasing activations in distinct regions of the striatum, irrespective of different combinations of magnitude and probability. Stimuli associated with higher uncertainty (variance) elicited increasing activations in the lateral orbitofrontal cortex. Uncertainty-related activations covaried with individual risk aversion in lateral orbitofrontal regions and risk-seeking in more medial areas. Furthermore, activations in expected value-coding regions in prefrontal cortex covaried differentially with uncertainty depending on risk attitudes of individual participants, suggesting that separate prefrontal regions are involved in risk aversion and seeking. These data demonstrate the distinct coding in key reward structures of the two basic and crucial decision parameters, expected value, and uncertainty. |
|
A Galvan, Todd Anthony Hare, H Voss, G Glover, B J Casey, Risk-taking and the adolescent brain: who is at risk?, Developmental Science, Vol. 10 (2), 2007. (Journal Article)
Relative to other ages, adolescence is described as a period of increased impulsive and risk-taking behavior that can lead to fatal outcomes (suicide, substance abuse, HIV, accidents, etc.). This study was designed to examine neural correlates of risk-taking behavior in adolescents, relative to children and adults, in order to predict who may be at greatest risk. Activity in reward-related neural circuitry in anticipation of a large monetary reward was measured with functional magnetic resonance imaging, and anonymous self-report ratings of risky behavior, anticipation of risk and impulsivity were acquired in individuals between the ages of 7 and 29 years. There was a positive association between accumbens activity and the likelihood of engaging in risky behavior across development. This activity also varied as a function of individuals' ratings of anticipated positive or negative consequences of such behavior. Impulsivity ratings were not associated with accumbens activity, but rather with age. These findings suggest that during adolescence, some individuals may be especially prone to engage in risky behaviors due to developmental changes in concert with variability in a given individual's predisposition to engage in risky behavior, rather than to simple changes in impulsivity. |
|
J Spicer, A Galvan, Todd Anthony Hare, H Voss, G Glover, B Casey, Sensitivity of the nucleus accumbens to violations in expectation of reward, NeuroImage, Vol. 34 (1), 2007. (Journal Article)
This study examined whether ventral frontostriatal regions differentially code expected and unexpected reward outcomes. We parametrically manipulated the probability of reward and examined the neural response to reward and nonreward for each probability condition in the ventral striatum and the orbitofrontal cortex (OFC). By late trials of the experiment, subjects showed slower behavioral responses for the condition with the lowest probability of reward, relative to the condition with the highest probability of reward. At the neural level, both the nucleus accumbens (NAcc) and OFC showed greater activation to rewarded relative to nonrewarded trials, but the accumbens appeared to be most sensitive to violations in expected reward outcomes. These data suggest distinct roles for frontostriatal circuitry in reward prediction and in responding to violations in expectations. |
|
S Bestmann, Christian Ruff, C Blakemore, J Driver, K V Thilo, Spatial attention changes excitability of human visual cortex to direct stimulation, Current Biology, Vol. 17 (2), 2007. (Journal Article)
Conscious perception depends not only on sensory input, but also on attention [1, 2]. Recent studies in monkeys [3-6] and humans [7-12] suggest that influences of spatial attention on visual awareness may reflect top-down influences on excitability of visual cortex. Here we tested this specifically, by providing direct input into human visual cortex via cortical transcranial magnetic stimulation (TMS) to produce illusory visual percepts, called phosphenes. We found that a lower TMS intensity was needed to elicit a conscious phosphene when its apparent spatial location was attended, rather than unattended. Our results indicate that spatial attention can enhance visual-cortex excitability, and visual awareness, even when sensory signals from the eye via the thalamic pathway are bypassed. |
|
R J Moran, S J Kiebel, Klaas Enno Stephan, R B Reilly, Jean Daunizeau, K J Friston, A neural mass model of spectral responses in electrophysiology, NeuroImage, Vol. 37 (3), 2007. (Journal Article)
We present a neural mass model of steady-state membrane potentials measured with local field potentials or electroencephalography in the frequency domain. This model is an extended version of previous dynamic causal models for investigating event-related potentials in the time-domain. In this paper, we augment the previous formulation with parameters that mediate spike-rate adaptation and recurrent intrinsic inhibitory connections. We then use linear systems analysis to show how the model's spectral response changes with its neurophysiological parameters. We demonstrate that much of the interesting behaviour depends on the non-linearity which couples mean membrane potential to mean spiking rate. This non-linearity is analogous, at the population level, to the firing rate-input curves often used to characterize single-cell responses. This function depends on the model's gain and adaptation currents which, neurobiologically, are influenced by the activity of modulatory neurotransmitters. The key contribution of this paper is to show how neuromodulatory effects can be modelled by adding adaptation currents to a simple phenomenological model of EEG. Critically, we show that these effects are expressed in a systematic way in the spectral density of EEG recordings. Inversion of the model, given such non-invasive recordings, should allow one to quantify pharmacologically induced changes in adaptation currents. In short, this work establishes a forward or generative model of electrophysiological recordings for psychopharmacological studies. |
|