Marco Prestipino, Gerhard Schwabe, Vernetzung, Virtualisierung und Wissen im Tourismus, In: Wissen, Vernetzung, Virtualisierung - Liber amicorum zum 65. Geburtstag von Prof. Dr. Udo Winand, J. Eul Verlag, Lohmar / Deutschland, p. 371 - 380, 2008. (Book Chapter)
Die Vernetzung der Individualreisenden über ihre begrenzten persönlichen Netze hinaus in virtuellen Gemeinschaften ermöglicht einen globalen Informationsaustausch und führt zur Virtualisierung touristischer Artefakte (z.B. Reiseberichte und Bilder) sowie durch die vereinfachte Kooperation zur Virtualisierung touristischer Informationsprodukte. Unsere Untersuchungen zeigen, dass die Qualität der Information mit kommerziellen Produkten gleichziehen kann. Gleichzeitig steht damit ein bislang fehlendes Instrumentarium zur Messung der Informationsqualität zur Verfügung.Damit ändern sich die Geschäftsmodelle im wissensintensiven Tourismusmarkt grundlegend, da die kommerzielle Herstellung von Information der kostenlosen, qualitativ und quantitativ leistungsfähigen Informationserstellung und -verteilung virtuellen Gemeinschaften gegenübersteht. |
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R C van Kleef, Konstantin Beck, F Buchner, How self-selection affects risk equalization: the example of voluntary deductibles, In: Voluntary deductibles and risk equalization: a complex interaction, Rotterdam, p. 43 - 64, 2008. (Book Chapter)
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David Hausheer, Cristian Morariu, Thomas Bocek, EmanicsLab: A distributed computing and storage testbed for EMANICS, 2008. (Other Publication)
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Todd Anthony Hare, N Tottenham, A Galvan, H U Voss, G H Glover, B J Casey, Biological substrates of emotional reactivity and regulation in adolescence during an emotional go-nogo task, Biological Psychiatry, Vol. 63 (10), 2008. (Journal Article)
BACKGROUND: Adolescence is a transition period from childhood to adulthood that is often characterized by emotional instability. This period is also a time of increased incidence of anxiety and depression, underscoring the importance of understanding biological substrates of behavioral and emotion regulation during adolescence. Developmental changes in the brain in concert with individual predispositions for anxiety might underlie the increased risk for poor outcomes reported during adolescence. We tested the hypothesis that difficulties in regulating behavior in emotional contexts in adolescents might be due to competition between heightened activity in subcortical emotional processing systems and immature top-down prefrontal systems. Individual differences in emotional reactivity might put some teens at greater risk during this sensitive transition in development.
METHODS: We examined the association between emotion regulation and frontoamygdala circuitry in 60 children, adolescents, and adults with an emotional go-nogo paradigm. We went beyond examining the magnitude of neural activity and focused on neural adaptation within this circuitry across time with functional magnetic resonance imaging.
RESULTS: Adolescents showed exaggerated amygdala activity relative to children and adults. This age-related difference decreased with repeated exposures to the stimuli, and individual differences in self-ratings of anxiety predicted the extent of adaptation or habituation in amygdala. Individuals with higher trait anxiety showed less habituation over repeated exposures. This failure to habituate was associated with less functional connectivity between ventral prefrontal cortex and amygdala.
CONCLUSIONS: These findings suggest that exaggerated emotional reactivity during adolescence might increase the need for top-down control and put individuals with less control at greater risk for poor outcomes |
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N Shea, K Krug, Philippe Tobler, Conceptual representations in goal-directed decision making, Cognitive, Affective & Behavioral Neuroscience, Vol. 8 (4), 2008. (Journal Article)
Emerging evidence suggests that the long-established distinction between habit-based and goal-directed decision-making mechanisms can also be sustained in humans. Although the habit-based system has been extensively studied in humans, the goal-directed system is less well characterized. This review brings to that task the distinction between conceptual and nonconceptual representational mechanisms. Conceptual representations are structured out of semantic constituents (concepts)--the use of which requires an ability to perform some language-like syntactic processing. Decision making--as investigated by neuroscience and psychology--is normally studied in isolation from questions about concepts as studied in philosophy and cognitive psychology. We ask what role concepts play in the "goal-directed" decision-making system. We argue that one fruitful way of studying this system in humans is to investigate the extent to which it deploys conceptual representations. |
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S Bestmann, Christian Ruff, J Driver, F Blankenburg, Concurrent TMS and functional magnetic resonance imaging: Methods and current advances, In: Oxford Handbook of Transcranial Stimulation, Oxford University Press, Oxford, UK, p. 569 - 592, 2008. (Book Chapter)
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Todd Anthony Hare, John O'Doherty, Colin F Camerer, Wolfram Schultz, Antonio Rangel, Dissociating the role of the orbitofrontal cortex and the striatum in the computation of goal values and prediction errors, Journal of Neuroscience, Vol. 28 (22), 2008. (Journal Article)
To make sound economic decisions, the brain needs to compute several different value-related signals. These include goal values that measure the predicted reward that results from the outcome generated by each of the actions under consideration, decision values that measure the net value of taking the different actions, and prediction errors that measure deviations from individuals' previous reward expectations. We used functional magnetic resonance imaging and a novel decision-making paradigm to dissociate the neural basis of these three computations. Our results show that they are supported by different neural substrates: goal values are correlated with activity in the medial orbitofrontal cortex, decision values are correlated with activity in the central orbitofrontal cortex, and prediction errors are correlated with activity in the ventral striatum. |
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Christian Ruff, S Bestmann, F Blankenburg, O Bjoertomt, O Josephs, N Weiskopf, R Deichmann, J Driver, Distinct causal influences of parietal versus frontal areas on human visual cortex: evidence from concurrent TMS-fMRI, Cerebral Cortex, Vol. 18 (4), 2008. (Journal Article)
It has often been proposed that regions of the human parietal and/or frontal lobe may modulate activity in visual cortex, for example, during selective attention or saccade preparation. However, direct evidence for such causal claims is largely missing in human studies, and it remains unclear to what degree the putative roles of parietal and frontal regions in modulating visual cortex may differ. Here we used transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI) concurrently, to show that stimulating right human intraparietal sulcus (IPS, at a site previously implicated in attention) elicits a pattern of activity changes in visual cortex that strongly depends on current visual context. Increased intensity of IPS TMS affected the blood oxygen level-dependent (BOLD) signal in V5/MT+ only when moving stimuli were present to drive this visual region, whereas TMS-elicited BOLD signal changes were observed in areas V1-V4 only during the absence of visual input. These influences of IPS TMS upon remote visual cortex differed significantly from corresponding effects of frontal (eye field) TMS, in terms of how they related to current visual input and their spatial topography for retinotopic areas V1-V4. Our results show directly that parietal and frontal regions can indeed have distinct patterns of causal influence upon functional activity in human visual cortex. |
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S Bestmann, O Swayne, F Blankenburg, Christian Ruff, P Haggard, N Weiskopf, O Josephs, J Driver, J C Rothwell, N S Ward, Dorsal premotor cortex exerts state-dependent causal influences on activity in contralateral primary motor and dorsal premotor cortex, Cerebral Cortex, Vol. 18 (6), 2008. (Journal Article)
During voluntary action, dorsal premotor cortex (PMd) may exert influences on motor regions in both hemispheres, but such interregional interactions are not well understood. We used transcranial magnetic stimulation (TMS) concurrently with event-related functional magnetic resonance imaging to study such interactions directly. We tested whether causal influences from left PMd upon contralateral (right) motor areas depend on the current state of the motor system, involving regions engaged in a current task. We applied short bursts (360 ms) of high- or low-intensity TMS to left PMd during single isometric left-hand grips or during rest. TMS to left PMd affected activity in contralateral right PMd and primary motor cortex (M1) in a state-dependent manner. During active left-hand grip, high (vs. low)-intensity TMS led to activity increases in contralateral right PMd and M1, whereas activity decreases there due to TMS were observed during no-grip rest. Analyses of condition-dependent functional coupling confirmed topographically specific stronger coupling between left PMd and right PMd (and right M1), when high-intensity TMS was applied to left PMd during left-hand grip. We conclude that left PMd can exert state-dependent interhemispheric influences on contralateral cortical motor areas relevant for a current motor task. |
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L M Harrison, W Penny, G Flandin, Christian Ruff, N Weiskopf, K J Friston, Graph-partitioned spatial priors for functional magnetic resonance images, NeuroImage, Vol. 43 (4), 2008. (Journal Article)
Spatial models of functional magnetic resonance imaging (fMRI) data allow one to estimate the spatial smoothness of general linear model (GLM) parameters and eschew pre-process smoothing of data entailed by conventional mass-univariate analyses. Recently diffusion-based spatial priors [Harrison, L.M., Penny, W., Daunizeau, J., and Friston, K.J. (2008). Diffusion-based spatial priors for functional magnetic resonance images. NeuroImage.] were proposed, which provide a way to formulate an adaptive spatial basis, where the diffusion kernel of a weighted graph-Laplacian (WGL) is used as the prior covariance matrix over GLM parameters. An advantage of these is that they can be used to relax the assumption of isotropy and stationarity implicit in smoothing data with a fixed Gaussian kernel. The limitation of diffusion-based models is purely computational, due to the large number of voxels in a brain volume. One solution is to partition a brain volume into slices, using a spatial model for each slice. This reduces computational burden by approximating the full WGL with a block diagonal form, where each block can be analysed separately. While fMRI data are collected in slices, the functional structures exhibiting spatial coherence and continuity are generally three-dimensional, calling for a more informed partition. We address this using the graph-Laplacian to divide a brain volume into sub-graphs, whose shape can be arbitrary. Their shape depends crucially on edge weights of the graph, which can be based on the Euclidean distance between voxels (isotropic) or on GLM parameters (anisotropic) encoding functional responses. The result is an approximation the full WGL that retains its 3D form and also has potential for parallelism. We applied the method to high-resolution (1 mm(3)) fMRI data and compared models where a volume was divided into either slices or graph-partitions. Models were optimized using Expectation-Maximization and the approximate log-evidence computed to compare these different ways to partition a spatial prior. The high-resolution fMRI data presented here had greatest evidence for the graph partitioned anisotropic model, which was best able to preserve fine functional detail. |
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T Kalenscher, Philippe Tobler, Interdisciplinary perspectives on decision making: Introduction, Cognitive, Affective & Behavioral Neuroscience, Vol. 8 (4), 2008. (Journal Article)
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F Blankenburg, Christian Ruff, S Bestmann, O Bjoertomt, N Eshel, O Josephs, N Weiskopf, J Driver, Interhemispheric effect of parietal TMS on somatosensory response confirmed directly with concurrent TMS-fMRI, Journal of Neuroscience, Vol. 28 (49), 2008. (Journal Article)
Transcranial magnetic stimulation (TMS) has been used to document some apparent interhemispheric influences behaviorally, with TMS over the right parietal cortex reported to enhance processing of touch for the ipsilateral right hand (Seyal et al., 1995). However, the neural bases of such apparent interhemispheric influences from TMS remain unknown. Here, we studied this directly by combining TMS with concurrent functional magnetic resonance imaging (fMRI). We applied bursts of 10 Hz TMS over right parietal cortex, at a high or low intensity, during two sensory contexts: either without any other stimulation, or while participants received median nerve stimulation to the right wrist, which projects to left primary somatosensory cortex (SI). TMS to right parietal cortex affected the blood oxygenation level-dependent signal in left SI, with high- versus low-intensity TMS increasing the left SI signal during right-wrist somatosensory input, but decreasing this in the absence of somatosensory input. This state-dependent modulation of SI by parietal TMS over the other hemisphere was accompanied by a related pattern of TMS-induced influences in the thalamus, as revealed by region-of-interest analyses. A behavioral experiment confirmed that the same right parietal TMS protocol of 10 Hz bursts led to enhanced detection of perithreshold electrical stimulation of the right median nerve, which is initially processed in left SI. Our results confirm directly that TMS over right parietal cortex can affect processing in left SI of the other hemisphere, with rivalrous effects (possibly transcallosal) arising in the absence of somatosensory input, but facilitatory effects (possibly involving thalamic circuitry) in the presence of driving somatosensory input. |
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S Bestmann, Christian Ruff, F Blankenburg, N Weiskopf, J Driver, J C Rothwell, Mapping causal interregional influences with concurrent TMS-fMRI, Experimental Brain Research, Vol. 191 (4), 2008. (Journal Article)
Transcranial magnetic stimulation (TMS) produces a direct causal effect on brain activity that can now be studied by new approaches that simultaneously combine TMS with neuroimaging methods, such as functional magnetic resonance imaging (fMRI). In this review we highlight recent concurrent TMS-fMRI studies that illustrate how this novel combined technique may provide unique insights into causal interactions among brain regions in humans. We show how fMRI can detect the spatial topography of local and remote TMS effects and how these may vary with psychological factors such as task-state. Concurrent TMS-fMRI may furthermore reveal how the brain adapts to so-called virtual lesions induced by TMS, and the distributed activity changes that may underlie the behavioural consequences often observed during cortical stimulation with TMS. We argue that combining TMS with neuroimaging techniques allows a further step in understanding the physiological underpinnings of TMS, as well as the neural correlated of TMS-evoked consequences on perception and behaviour. This can provide powerful new insights about causal interactions among brain regions in both health and disease that may ultimately lead to developing more efficient protocols for basic research and therapeutic TMS applications. |
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Philippe Tobler, G I Christopoulos, J P O'Doherty, R J Dolan, W Schultz, Neuronal distortions of reward probability without choice, Journal of Neuroscience, Vol. 28 (45), 2008. (Journal Article)
Reward probability crucially determines the value of outcomes. A basic phenomenon, defying explanation by traditional decision theories, is that people often overweigh small and underweigh large probabilities in choices under uncertainty. However, the neuronal basis of such reward probability distortions and their position in the decision process are largely unknown. We assessed individual probability distortions with behavioral pleasantness ratings and brain imaging in the absence of choice. Dorsolateral frontal cortex regions showed experience dependent overweighting of small, and underweighting of large, probabilities whereas ventral frontal regions showed the opposite pattern. These results demonstrate distorted neuronal coding of reward probabilities in the absence of choice, stress the importance of experience with probabilistic outcomes and contrast with linear probability coding in the striatum. Input of the distorted probability estimations to decision-making mechanisms are likely to contribute to well known inconsistencies in preferences formalized in theories of behavioral economics. |
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B Schenkluhn, Christian Ruff, K Heinen, C D Chambers, Parietal stimulation decouples spatial and feature-based attention, Journal of Neuroscience, Vol. 28 (44), 2008. (Journal Article)
Everyday visual scenes contain a vast quantity of information, only a fraction of which can guide our behavior. Properties such as the location, color and orientation of stimuli help us extract relevant information from complex scenes (Treisman and Gelade, 1980; Livingstone and Hubel, 1987). But how does the brain coordinate the selection of such different stimulus characteristics? Neuroimaging studies have revealed significant regions of overlapping activity in frontoparietal cortex during attention to locations and features, suggesting a global component to visual selection (Vandenberghe et al., 2001; Corbetta and Shulman, 2002; Giesbrecht et al., 2003; Slagter et al., 2007). At the same time, the neural consequences of spatial and feature-based attention differ markedly in early visual areas (Treue and Martinez-Trujillo, 2007), implying that selection may rely on more specific top-down processes. Here we probed the balance between specialized and generalized control by interrupting preparatory attention in the human parietal cortex with transcranial magnetic stimulation (TMS). We found that stimulation of the supramarginal gyrus (SMG) impaired spatial attention only, whereas TMS of the anterior intraparietal sulcus (aIPS) disrupted spatial and feature-based attention. The selection of different stimulus characteristics is thus mediated by distinct top-down mechanisms, which can be decoupled by cortical interference. |
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J Fujiwara, Philippe Tobler, M Taira, T Iijima, K I Tsutsui, Personality-dependent dissociation of absolute and relative loss processing in orbitofrontal cortex, European Journal of Neuroscience, Vol. 27 (6), 2008. (Journal Article)
A negative outcome can have motivational and emotional consequences on its own (absolute loss) or in comparison to alternative, better, outcomes (relative loss). The consequences of incurring a loss are moderated by personality factors such as neuroticism and introversion. However, the neuronal basis of this moderation is unknown. Here we investigated the neuronal basis of loss processing and personality with functional magnetic resonance imaging in a choice task. We separated absolute and relative financial loss by sequentially revealing the chosen and unchosen outcomes. With increasing neuroticism, activity in the left lateral orbitofrontal cortex (OFC) preferentially reflected relative rather than absolute losses. Conversely, with increasing introversion, activity in the right lateral OFC preferentially reflected absolute rather than relative losses. These results suggest that personality affects loss-related processing through the lateral OFC, and propose a dissociation of personality dimension and loss type on the neuronal level. |
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B Pleger, F Blankenburg, Christian Ruff, J Driver, R J Dolan, Reward facilitates tactile judgments and modulates hemodynamic responses in human primary somatosensory cortex, Journal of Neuroscience, Vol. 28 (33), 2008. (Journal Article)
Reinforcing effects of reward on action are well established, but possible effects on sensory function are less well explored. Here, using functional magnetic resonance imaging, we assessed whether reward can influence somatosensory judgments and modulate activity in human somatosensory cortex. Participants discriminated electrical somatosensory stimuli on an index finger with correct performance rewarded financially at trial end, at one of four different anticipated levels. Higher rewards improved tactile performance and led to increased hemodynamic signals from ventral striatum on rewarded trials. Remarkably, primary somatosensory cortex contralateral to the judged hand was reactivated at the point of reward delivery, despite the absence of concurrent somatosensory input at that time point. This side-specific reactivation of primary somatosensory cortex increased monotonically with level of reward. Moreover, the level of reward received on a particular trial influenced somatosensory performance and neural activity on the subsequent trial, with better discrimination and enhanced hemodynamic response in contralateral primary somatosensory cortex for trials that followed higher rewards. These results indicate that rewards can influence not only classical reward-related regions, but also early somatosensory cortex when a decision is required for that modality. |
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B J Casey, Rebecca M Jones, Todd Anthony Hare, The adolescent brain, Annals of the New York Academy of Sciences, Vol. 1124, 2008. (Journal Article)
Adolescence is a developmental period characterized by suboptimal decisions and actions that are associated with an increased incidence of unintentional injuries, violence, substance abuse, unintended pregnancy, and sexually transmitted diseases. Traditional neurobiological and cognitive explanations for adolescent behavior have failed to account for the nonlinear changes in behavior observed during adolescence, relative to both childhood and adulthood. This review provides a biologically plausible model of the neural mechanisms underlying these nonlinear changes in behavior. We provide evidence from recent human brain imaging and animal studies that there is a heightened responsiveness to incentives and socioemotional contexts during this time, when impulse control is still relatively immature. These findings suggest differential development of bottom-up limbic systems, implicated in incentive and emotional processing, to top-down control systems during adolescence as compared to childhood and adulthood. This developmental pattern may be exacerbated in those adolescents prone to emotional reactivity, increasing the likelihood of poor outcomes. |
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Philippe Tobler, A Kalis, T Kalenscher, The role of moral utility in decision making: an interdisciplinary framework, Cognitive, Affective & Behavioral Neuroscience, Vol. 8 (4), 2008. (Journal Article)
What decisions should we make? Moral values, rules, and virtues provide standards for morally acceptable decisions, without prescribing how we should reach them. However, moral theories do assume that we are, at least in principle, capable of making the right decisions. Consequently, an empirical investigation of the methods and resources we use for making moral decisions becomes relevant. We consider theoretical parallels of economic decision theory and moral utilitarianism and suggest that moral decision making may tap into mechanisms and processes that have originally evolved for nonmoral decision making. For example, the computation of reward value occurs through the combination of probability and magnitude; similar computation might also be used for determining utilitarian moral value. Both nonmoral and moral decisions may resort to intuitions and heuristics. Learning mechanisms implicated in the assignment of reward value to stimuli, actions, and outcomes may also enable us to determine moral value and assign it to stimuli, actions, and outcomes. In conclusion, we suggest that moral capabilities can employ and benefit from a variety of nonmoral decision-making and learning mechanisms. |
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J W Rieger, N Köchy, F Schalk, Marcus Grüschow, H J Heinze, Speed limits: orientation and semantic context interactions constrain natural scene discrimination dynamics, Journal of Experimental Psychology: Human Perception and Performance, Vol. 34 (1), 2008. (Journal Article)
The visual system rapidly extracts information about objects from the cluttered natural environment. In 5 experiments, the authors quantified the influence of orientation and semantics on the classification speed of objects in natural scenes, particularly with regard to object-context interactions. Natural scene photographs were presented in an object-discrimination task and pattern masked with various scene-to-mask stimulus-onset asynchronies (SOAs). Full psychometric functions and reaction times (RTs) were measured. The authors found that (a) rotating the full scenes increased threshold SOA at intermediate rotation angles but not for inversion; (b) rotating object or context degraded classification performance in a similar manner; (c) semantically congruent contexts had negligible facilitatory effects on object classification compared with meaningless baseline contexts with a matching contrast structure, but incongruent contexts severely degraded performance; (d) any object-context incongruence (orientation or semantic) increased RTs at longer SOAs, indicating dependent processing of object and context; and (e) facilitatory effects of context emerged only when the context shortly preceded the object. The authors conclude that the effects of natural scene context on object classification are primarily inhibitory and discuss possible reasons. |
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