Publications des institutions partenaires
Reward value coding distinct from risk attitude-related uncertainty coding in human reward systems
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...
Institution partenaire
English / 01/01/2007
Comparing risky and inter-temporal decisions: Views from psychology, ecology and microeconomics
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...
Institution partenaire
English / 01/01/2007
Sensitivity of the nucleus accumbens to violations in expectation of reward
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...
Institution partenaire
English / 01/01/2007
Risk-taking and the adolescent brain: who is at risk?
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-...
Institution partenaire
English / 01/01/2007
Analysis of anatomical and effective connectivity in neural systems
Institution partenaire
English / 01/01/2007
Free-energy and the brain
If one formulates Helmholtz's ideas about perception in terms of modern-day theories one arrives at a model of perceptual inference and learning that can explain a remarkable range of neurobiological facts. Using constructs from statistical physics it can be shown that the problems of inferring what cause our sensory input and learning causal regularities in the sensorium can be...
Institution partenaire
English / 01/01/2007
Parieto-frontal connectivity during visually guided grasping
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...
Institution partenaire
English / 01/01/2007
Comparing hemodynamic models with DCM
The classical model of blood oxygen level-dependent (BOLD) responses by Buxton et al. [Buxton, R.B., Wong, E.C., Frank, L.R., 1998. Dynamics of blood flow and oxygenation changes during brain activation: the Balloon model. Magn. Reson. Med. 39, 855-864] has been very important in providing a biophysically plausible framework for explaining different aspects of hemodynamic responses....
Institution partenaire
English / 01/01/2007
A neural mass model of spectral responses in electrophysiology
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...
Institution partenaire
English / 01/01/2007
Hierarchical processing of auditory objects in humans
This work examines the computational architecture used by the brain during the analysis of the spectral envelope of sounds, an important acoustic feature for defining auditory objects. Dynamic causal modelling and Bayesian model selection were used to evaluate a family of 16 network models explaining functional magnetic resonance imaging responses in the right temporal lobe during...
Institution partenaire
English / 01/01/2007
Dynamic causal modelling of evoked potentials: a reproducibility study
Dynamic causal modelling (DCM) has been applied recently to event-related responses (ERPs) measured with EEG/MEG. DCM attempts to explain ERPs using a network of interacting cortical sources and waveform differences in terms of coupling changes among sources. The aim of this work was to establish the validity of DCM by assessing its reproducibility across subjects. We used an oddball...
Institution partenaire
English / 01/01/2007
Dynamic causal models of neural system dynamics:current state and future extensions
Complex processes resulting from interaction of multiple elements can rarely be understood by analytical scientific approaches alone; additional, mathematical models of system dynamics are required. This insight, which disciplines like physics have embraced for a long time already, is gradually gaining importance in the study of cognitive processes by functional neuroimaging. In this...
Institution partenaire
English / 01/01/2007
Interhemispheric integration of visual processing during task-driven lateralization
The mechanisms underlying interhemispheric integration (IHI) remain poorly understood, particularly for lateralized cognitive processes. To test competing theories of IHI, we constructed and fitted dynamic causal models to functional magnetic resonance data from two visual tasks that operated on identical stimuli but showed opposite hemispheric dominance. Using a systematic Bayesian...
Institution partenaire
English / 01/01/2007
Approaches to the cortical analysis of auditory objects
We describe work that addresses the cortical basis for the analysis of auditory objects using 'generic' sounds that do not correspond to any particular events or sources (like vowels or voices) that have semantic association. The experiments involve the manipulation of synthetic sounds to produce systematic changes of stimulus features, such as spectral envelope....
Institution partenaire
English / 01/01/2007
Neurophysiological correlates of relatively enhanced local visual search in autistic adolescents
Previous studies found normal or even superior performance of autistic patients on visuospatial tasks requiring local search, like the Embedded Figures Task (EFT). A well-known interpretation of this is "weak central coherence", i.e. autistic patients may show a reduced general ability to process information in its context and may therefore have a tendency to favour local...
Institution partenaire
English / 01/01/2007
Extra-classical receptive field effects measured in striate cortex with fMRI
The aim of this study was to measure the contextual influence of globally coherent motion on visual cortical responses using functional magnetic resonance imaging. Our motivation was to test a prediction from representational theories of perception (i.e. predictive coding) that primary visual responses should be suppressed by top-down influences during coherent motion. We used a...
Institution partenaire
English / 01/01/2007
Mechanisms of hemispheric specialization: insights from analyses of connectivity
Traditionally, anatomical and physiological descriptions of hemispheric specialization have focused on hemispheric asymmetries of local brain structure or local functional properties, respectively. This article reviews the current state of an alternative approach that aims at unraveling the causes and functional principles of hemispheric specialization in terms of asymmetries in...
Institution partenaire
English / 01/01/2007
Models of effective connectivity in neural systems
It is a longstanding scientific insight that understanding processes that result from the interaction of multiple elements require mathematical models of system dynamics (von Bertalanffy 1969). This notion is an increasingly important theme in neuroscience, particularly in neuroimaging, where causal mechanisms in neural systems are described in terms of effective connectivity. Here,...
Institution partenaire
English / 01/01/2007
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