21 January 2011
Presentation type: Science
Cristian Carmeli, LREN, CHUV
"EEG synchronization topography of sensor and source signals"
Cortical functioning involves the formation of cooperative neuronal assemblies characterized by synchronous oscillatory activity. We introduce a method to estimate synchronization of multivariate signals derived from dynamical systems theory. Through a surface topography of multivariate sensors-EEG synchronization, we assess visual stimuli induced interhemispheric synchronization. In Alzheimer's disease, we reveal a specific landscape of hyper and hypo-synchronized clusters through a whole-brain mapping of multivariate source-EEG synchronization.
Presentation type: Methods
Ferath Kherif, LREN, CHUV
"Multivariate toolbox for SPM"
Introduction to the methods implemented in the Multivariate toolbox for SPM. As an example of application we compute multivariate composite measures of age-related tissue properties changes. We applied a voxel-based multivariate analysis (MANOVA) and classification/prediction procedure on structural relaxometry-based MRI data in order to build optimal composite predictors of age-related tissue properties changes.
28 January 2011
Presentation type: Science
Katrin Walther, Tucson, Arizona USA
"Modifiers of brain function and structure in older adults"
Aging is marked by substantial individual differences in cognitive functioning and their neural substrates. The reasons why some, but not other, individuals retain their cognitive function in old age are poorly understood. In my presentation I will focus on multiple factors affecting brain aging and risk for age-related cognitive impairment. The studies assessed risk factors (APOE, obesity) and protective factors (anti-inflammatory drugs) in relation to brain structure and function in cognitively healthy older adults. In addition, I will present results of an fMRI experiment examining individual differences in compensatory activation in a source memory task.
04 February 2011 - location Séminaire DG - BH08.629
Presentation type: Science
Jürgen Dukart, MPI, Leipzig Germany
"Impact of preprocessing and advantages of multimodal evaluation to improve understanding, detection and differentiation of dementia"
In recent research, various biomarkers have been investigated regarding imaging abnormalities in different types of dementia. However, to enable a valid statistical evaluation imaging data usually require a lot of preprocessing steps. Thereby, different preprocessing procedures might substantially affect the statistical outcome – a fact which is frequently neglected in clinical studies. I will discuss some aspects in preprocessing of single- and multimodal imaging data on the example of FDG-PET and structural and resting state MRI. Further, I will present some clinical examples of how multimodal imaging information might be combined to improve understanding, detection and differentiation of specific dementia syndromes.
Presentation type: Methods
Athina Tzovara, CHUV
"Prediction of exploratory decision-making from single-trial topographic EEG analyses"
Decision-making in an uncertain environment is driven by two major needs: exploring the environment to gather information or exploiting acquired knowledge to maximize reward. The processes underlying exploratory decision-making have been mainly studied by means of functional magnetic resonance imaging leaving their temporal aspects under-explored. Here, we use a well-known gambling paradigm in reinforcement learning to assess the neural correlates of exploratory decision-making. The aim is to predict subjects’ decisions on the next trial and to detect when this decision is taken. To establish this prediction, we classified single-trial EEG voltage topographies during reward evaluation. Because the timing of the decision varies across trials, we extracted non-time-locked topographies and evaluated when there was sufficient evidence to reliably predict the subject’s choice. Classification accuracy for seven subjects, measured as the area under the Receiver Operator’s Characteristic curve, was on average 0.65. On an individual subject basis, distributed source estimations were performed on the topographies extracted in order to statistically evaluate the neural correlates of decision making. For trials leading to exploration, there was significantly higher activity in dorsolateral prefrontal cortex and in the right parietal supramarginal gyrus; areas known to be responsible for task-switching and in modulating behavior under risk and deduction. No area was more active during exploitation, further supporting the theory that exploration overrides exploitative tendencies. We show for the first time the temporal evolution of differential patterns of brain activation in an exploratory decision-making task on a single-trial basis.
11 February 2011
Presentation type: Methods
Marie Schaer, HUG Geneva
"Local Gyrification Index: method and application in cohorts with normal or abnormal brain development"
An increasing interest has recently been devoted to the study of cortical convolutions, as a window to reveal some aspects of early brain development. For that purpose, we have recently proposed a surface-based method for the quantification of cortical folding. Our method uses accurate three-dimensional cortical reconstructions and computes local measurements of gyrification at thousands of points over the whole cortical surface. The local Gyrification Index method (lGI) has been made freely available to the scientific community through the FreeSurfer software (http://surfer.nmr.mgh.harvard.edu/fswiki/LGI).
Presentation type: Master's thesis - oral defense
Nathalie Charriere, LREN
"Brain structure-behaviour correlation analysis based on automated lesion detection in stroke"
18 February 2011
Presentation type: Science
Giovanni Battistella, CHUV
"Mapping the acute effects of marijuana on driving abilities"
Cannabinoids constitute the most commonly detected drugs in the blood of suspected impaired drivers. While this statistics underscore the potential harms associated with cannabis use, the cognitive functions involved in safe driving and their modifications due to drug use remain mostly unexplored. The aim of our study is to evaluate the impact of cannabis on the driving abilities of occasional smokers, by investigating changes in the brain network involved in a divided attention task.
Presentation type: Methods
Maria Joao, FIL, London, UK
"Comparing neurovascular coupling models using EEG-fMRI data"
The neurovascular coupling, or relationship between local neuronal activity and blood flow, is still under debate. In this talk I will present a biophysically informed generative model for EEG and fMRI signals that, together with Bayesian model selection and EEG-fMRI data, can be used to investigate the neurovascular coupling. In particular, I will compare different biologically plausible mechanisms and provide evidence that the coupling is frequency-dependent.
25 February 2011
Presentation type: Science
Rosanna De Meo, FENL, CHUV
"Impact of emotion, sleep and repeated testing on face-name association learning"
In this study, we were interested in three ways to improve learning of face-name associations, namely emotion (emotional vs neutral faces), sleep and repeated testing (one week later) without feed-back. Sixteen healthy controls learned 40 face-name associations and were asked to recall names. I will present the results we found and possible future investigations.
Presentation type: Methods
Nathalie Just, EPFL
"Investigating BOLD functional MRI and MRS in rats and mice: from the hemodynamic response to the metabolic response"
In rodents, BOLD fMRI studies are useful to understand and interpret the underlying molecular and physiological mechanisms of brain activation despite the use of anesthesia. A BOLD fMRI study of the primary somatosensory barrel cortex in rats and mice during trigeminal nerve stimulation was conducted allowing a robust and reproducible characterization of BOLD responses during barrel cortex activation. In addition, the proton neurochemical profile during barrel cortex activation was measured with 1H functional MR spectroscopy (fMRS) at 9.4T.
04 March 2011
Presentation type: Science
Alexander Rauch, MPI, Tübingen, Germany
"The Effects of Neuromodulation on Neurovascular Coupling in Monkeys studied by Functional Magnetic Resonance Imaging in combination with Neurophysiology and Neurochemistry"
To enable reliable and sensitive diagnostics by fMRI we need a better understanding of how neurodegenerative disorders may affect the BOLD signal. The majority of these disorders are often characterized by a certain degree of dysregulation of neuromodulators. We have therefore set out to study neurovascular coupling at neuromodulator-specific sites in non-human primates by using pharmacological functional imaging (using pharmacological manipulations). To ensure that any induced BOLD effects are indeed related to neuromodulators we simultaneously monitored neurochemical activity intracortically. Our approach allowed us to successfully establish the relationship between BOLD- and neuronal responses following injections of serotonin and acetylcholine, most recently dopamine. All in all, the results of these experiments show neuromodulator-specific effects on the BOLD signal which can be – in principle – further extended and eventually exploited for the early diagnosis of neurodegenerative disorders.
11 March 2011
Presentation type: Science
Johannes Rüter, EPFL
“Paradoxical evidence integration in rapid decision processes.”
Decisions about noisy stimuli require evidence integration over time. Traditionally, evidence integration and decision making are described as a one-stage process: a decision is made when evidence for the presence of a stimulus crosses a threshold. However, this model is incompatible with psychophysical experiments on feature fusion, where two visual stimuli are presented in rapid succession. Paradoxically, the second stimulus biases decisions more strongly than the first one, contrary to predictions of one-stage models and intuition. This can only be explained using a two-stage model where sensory information is integrated and buffered before it is fed into a drift diffusion process. I will present a series of psychophysical experiments to test both, accuracy and reaction time distributions predicted by the model.
Presentation type: Science
Hadas Okon-Singer, MPI Leipzig, Germany
"Neuro-Cognitive Modulation of Emotional Reactions to Stress."
Essential hypertension (EH), the most important risk factor of cardio- and cerebro-vascular disease today, is associated with enhanced emotional reaction, as well as anatomical and cognitive abnormalities. Recent findings suggest that these abnormalities are important in the initiation and maintenance of EH. We examined whether poor cognitive control over emotional reaction in young healthy subjects is associated with higher autonomic responses, including blood pressure.
18 March 2011
Presentation type: Methods
Marie-Christine Ottet, HUG Geneva
"Altered Structural Connectivity in 22q11 Deletion Syndrome: From the Human Connectome to Complex Network Analysis"
Velo-cardio-facial syndrome known also as 22q11DS, is a genetically deleted population that shows a prevalence for developing schizophrenia of 30%. Brain morphological abnormalities due to this chromosomal deletion are likely to provoke this higher risk. Using the Human Connectome technique (see the method in Hagmann et al. 2008), we show an alteration of structural brain connectivity in the 22q11DS population inside and between lobes.
Presentation type: Science
Wietske van der Zwaag, EPFL
"Digit somatotopic mapping in the human cerebellum."
The human cerebellum is a relatively little studied area because of it's small size and intricate structure. This means the spatial resolution necessary to resolve the cerebellar gray matter is significantly higher than what is typically used for fMRI. Here, the high BOLD sensitivity and spatial resolution available at 7T are employed to obtain a somatotopic map of the fingers in the cerebellum.
25 March 2011
Presentation type: Science
Ricardo Chavarriaga, EPFL
"Research on non-invasive neuroprosthetics at EPFL"
A non-invasive brain-computer interface (BCI) is a system that translates user's intent, coded by spatio-temporal neural activity (usually EEG), into a control signal without using activity of any muscles or peripheral nerves. Although BCIs are limited by a low information transfer rate, it has been shown that they can indeed be used for controlling very complex devices. In this talk I'll present the usage of these techniques on clinical applications for motor substitution and rehabilitation.
Specifically, I'll show how online asynchronous analysis of spontaneous EEG signals can be used to control mobile robots (e.g. automated wheelchairs), or neuroprosthesis (e.g. BCI controlled FES). The principle relies on statistical machine learning techniques in combination with shared control.
Presentation type: Methods
Gangadhar Garipelli, EPFL
"Multiple facets of anticipatory behavior revealed from distinctive EEG oscillations"
Most EEG studies of anticipatory behavior are based on the well known Contingent Negative Variation (CNV) protocol. Most often, the underlying anticipatory behavior is explained using negative Slow Cortical Potentials (SCPs) as a partial pre-activation of central cortical areas. We present our observations from an experiment conducted using a variation of the CNV protocol with multiple warning stimuli. We discuss changes in various frequency bands that are likely to be reflecting different traits of the anticipatory behavior.
01 April 2011
LREN celebrating 1st anniversary
08 April 2011
Presentation type: Science
Roberto Caldara, Fribourg
"Mapping the role of culture and race in face processing: from eye movements into neural coding"
Human beings living in different geographical locations can be categorized by culture and race. I will present eye movement studies challenging the view that the biologically-relevant face recognition and categorization of facial expressions of emotion are universally achieved across human beings. I will then present electrophysiological studies showing a very early extraction of race information from faces, which is related to a particular neural coding in the Fusiform Face Area (FFA). Our neuroimaging studies show when, where and how race categorization impacts upon face processing.
15 April 2011
Presentation type: Science
Kamiar Aminian, GaitLab EPFL/CHUV
"Mobility assessment in Parkinson disease: new possibilities and challenges"
The presentation addresses the relevance of wearable sensors for monitoring motor function. Ambulatory techniques for gait analysis, physical activity monitoring and mobility functional tests will be presented with specially focusing on mobility assessment in Parkinson disease patients.
Presentation type: Methods
Anishoara Ionescu, GaitLab EPFL/CHUV
"Complexity in physical activity patterns: steps toward a clinical evaluation tool"
This aim of this presentation is to introduce basic concepts related to definition of physical activity patterns, embedded dynamical complexity and objective complexity-based outcome measures in clinical evaluation.More specifically, the following questions will be addressed:1) How to define physical activity patterns, 2) How to quantify clinically relevant information embedded in physical activity patterns, 3) How the concept of ‘physiological complexity’ emerged and reshaped medical thinking about health and disease, 4) How complexity of physical activity patterns may provide outcome evaluation in chronic pain and depression.
22/29 April 2011
Easter Holidays
6 May 2011
Presentation type: Science
Frederic Assal, HUG/CHUV
"Associative memory and dementia"
Alzheimer’s disease (AD) is the major cause of dementia. Amnestic Mild Cognitive Impairment (aMCI) is a condition which involves an isolated episodic memory disorder and no dementia. Since not all patients with aMCI will develop AD, it is crucial to identify these patients who are most likely showing early signs of AD, and who may potentially benefit from future disease-modifying treatments. Structural MRI and functional imaging such as PET or SPECT and cerebrospinal fluid markers (Tau, Abeta) help the diagnosis of AD. fMRI studies have found changes in brain activation patterns during cognitive tasks in MCI patients relative to healthy elderly controls, as well as in aMCI patients who later converted to AD relative to patients who remained stable. Results, however, have not been very consistent between studies. We designed an associative memory fMRI paradigm in order to disentangle the neural underpinnings of different cognitive deficits associated with memory problems in aMCI. Our preliminary results showed that this fMRI paradigm is sensitive to deficits in several crucial components of memory function in aMCI and reliably discriminated between patients and controls. We hope this fMRI paradigm may be used as an early marker of AD in a longitudinal cohort of aMCI patients.
13 May 2011
Presentation type: Science
Joachim Forget, Radiology Dept CHUV & Laboratory of Cognitive Neuroscience EPFL
"Visual Integration of brief visual events in the stream of consciousness"
When two displays are presented in close temporal succession at the same location, how does the brain assign them to one versus two conscious percepts? We investigate this issue using a novel reading paradigm in which the odd and even letters of a string are presented alternatively at a variable rate. ERPs indicate that, even at the fastest frequency, the oscillating stimulus elicits synchronous oscillations in posterior visual cortices, while late ERP components sensitive to lexical status vanish beyond the fusion threshold. Thus, the fusion/segregation dilemma is not resolved by retinal or subcortical filtering, but at cortical level by at most 300 msec. The results argue against theories of visual word recognition and letter binding that rely on temporal synchrony or other fine temporal codes.
Presentation type: Science
Juergen Dukart, LREN/DNC/CHUV
"Relationship between Biomarkers, Age, Progression and Symptom Severity in Alzheimer’s Disease and Mild Cognitive Impairment"
Progression and pattern of changes in different biomarkers of Alzheimer’s disease (AD) and mild cognitive impairment (MCI) like [18F]fluorodeoxyglucose positron emission tomography (FDG-PET) and magnetic resonance imaging (MRI) have been carefully investigated over the past decades. However, little is known about how the dynamics of these changes are associated with specific demographic and cognitive variables. Here we investigated the relationship between age, time-to-conversion, symptom severity and functional (FDG-PET) and structural changes (MRI) in AD and MCI.
20 May 2011
Presentation type: Science
Olaf Blanke, Laboratory of Cognitive Neuroscience, Brain Mind Institute - EPFL
"The neuroscience of self-consciousness: From bodily processing to subjectivity"
Subjectivity is one of the most astonishing features of the human mind. Subjective experience is immediate and felt as my experience, whenever I am consciously perceiving the world, or whenever I am thinking a thought. Subjectivity or self-consciousness has fascinated layman and scholar from time immemorial and influenced our moral principles such as those of individuality, and free will. Despite massive novel insights into the workings of the human brain, these have not been applied to self-consciousness, which continues to be almost exclusively to be approached by philosophical enquiry leading to an overabundance of diverging theories and opinions.
I will present recent data in humans on the relevance of bodily self-consciousness, i.e., the processing of body-related information by the brain, as one promising approach for the development of a comprehensive neurobiological model of self-consciousness. (1) The experimental manipulation of bodily self-consciousness in healthy subjects using multisensory and/or sensorimotor conflict and virtual reality technology. (2) Neuroimaging data during experimentally altered states of bodily self-consciousness using an exciting new research platform that merges virtual reality and robotics with high-resolution EEG and fMRI. Both sets of data will be linked to data in (3) neurological patients suffering from altered states of bodily self-consciousness. I will conclude with a data-driven neuroscientific theory of self-consciousness and subjectivity.
27 May 2011
Presentation type: Science
Anjali Nursimulu, Laboratory for Decision-Making under Uncertainty (LDMU), EPFL.
"Topographic Electrophysiological Signatures of Decision-Making under Risk: A Factor Analysis"
Moment-based decision-making is a cornerstone of modern finance theory. The neural imprints of these mathematical moments – mean, variance and skewness - have been under scrutiny since the advent of Neuroeconomics, but primarily through the lens of functional neuroimaging. Thus, while the spatial neural correlates of the mathematical moments are known, their temporal dynamics are not. In the context of a novel risk-taking paradigm in which subjects decided whether or not to buy into a lottery at a posted price and pre-cued probability, these temporal patterns were investigated. Tensor analysis of event-related potentials (ERPs) allowed the dissociation of sensory and cognitive processes. Contextual modulation of the ventral and dorsal visual streams by probability and price was observed. The results also indicate that latent risk-related features namely, variance and skewness, are extracted within the first 350ms. Moreover, the associated time courses are suggestive of different underlying functional mechanisms
At Ayse, CHUV
"The role of the right parietal cortex in sound localization: a chronometric single-pulse TMS study"
Auditory spatial functions, including the ability to discriminate between the position of nearby sound sources, are subserved by a large temporo-parieto-frontal “where” network. With the aim of determining whether and when the right parietal cortex is critical for auditory spatial discrimination, we applied single pulse transcranial magnetic stimulation (TMS) on right parietal regions 20, 80, 90 and 150ms post-sound 1 onset while participants (n= 15 in Exp 1 and n= 13 in Exp 2) completed a two-alternative forced choice auditory spatial discrimination task between pairs of sounds presented within the left (Exp 1) or right hemispace (Exp 2). Our results reveal that transient TMS disruption of right parietal activity impairs spatial discrimination when applied at 20 ms post-stimulus onset for sounds presented in the left controlateral hemispace and at 80 ms for sound presented in the right ipsilateral hemispace. We interpret our finding in terms of a critical role for controlateral temporo-parietal networks over initial stages of the building-up of auditory spatial representations and for a right hemispheric specialization in integrating the whole auditory space over subsequent, higher-order processing stages.
10 June 2011
Presentation type: Science
Romana Rytsar, LREN/DNC/CHUV
“Effective connectivity changes in Alzheimer’s desease”
Changes of functional connectivity in prodromal and early Alzheimer’s disease can arise from compensatory and/or pathological processes. We hypothesized that i) there is impairment of effective inhibition associated with early Alzheimer’s disease that may lead to ii) a paradoxical increase of functional connectivity. To this end we analyzed effective connectivity in 14 patients and 16 matched controls using dynamic causal modeling of functional MRI time series recorded during a visual inter-hemispheric integration task.
Alzheimer’s disease was associated with significantly weakened intrinsic and modulatory connections. Top-down inhibitory effects, previously detected as relative deactivations of V1 in young adults, were observed neither in our aged controls nor in patients. We conclude that effective inhibition weakens with age and more so in early Alzheimer’s disease.
Presentation type: Science
Alexis Hervais-Adelman, Functional Brain Mapping Lab/UNIGE
"Managing simultaneity in speech: fMRI Investigation of Speech Shadowing and Simultaneous Interpretation"
Speech shadowing is a demanding task which requires listeners to repeat speech as they hear it, tracking it as closely as possible in time. The process of shadowing encompasses perceptual as well as production aspects of speech processing. In order to carry out shadowing effectively, speakers must be able to simultaneously handle listening to an input stream while monitoring their own production of the content of that stream. An even more challenging task is simultaneous interpretation, which further requires the conversion of the message of speech from one language to another, while respecting the phonetic, semantic, syntactic, and prosodic rules of this other language, all in real time.
Only a handful of studies have examined the neural substrates of simultaneous interpretation, and these have focused on expert interpreters. Here I will present an ongoing investigation into the neural substrates of both interpretation and shadowing, and the executive control structures that are implicated in dealing with simultaneous speech reception, translation and production, in a group of non-expert multilingual individuals and apprentice interpreters at the beginning of their professional training.
17 June 2011
Presentation type: Science
Christoph M. Michel, Neuroscience Department, University Medical School, Geneva
"Combining Electrical and Hemodynamic Brain Imaging in experimental and clinical studies"
Simultaneous recording of EEG and fMRI are particularly applied in two research domains: 1) in epilepsy, where the EEG is used to mark epileptic events that are correlated with the BOLD responses to determine epileptic foci, and 2) in studies on resting state networks in order to study neuronal correlates of the low-frequency BOLD fluctuations at rest. In both cases, the EEG is only used to quantify certain neuronal activity (frequency power or spikes). The capability of EEG as an imaging method is thereby ignored, despite major recent advances on spatial analysis and source imaging of multichannel EEG. I will illustrate the advantage of using EEG imaging methods to interpret the fMRI signals, both in epilepsy diagnostics as well as in research on resting state networks.
01 July 2011
Presentation type: Science
Raphaël Burgener, EPFL/CHUV
"Quantitative image analysis of damaged brains: study of acute stroke"
To detect and delineate strokes on T1-weighted magnetic resonance images in a reliable and fast manner, the author introduced a multivariate mixture of gaussians based on three image features : intensity, folding and thickness, coupled with an outlier detection. Then, the result is refined by a region-based reweighting, a region growing algorithm and a final step made by the segmentation process embedded in SPM8. The method is tested on simulated strokes as well as real strokes.
Presentation type: Project
Silvio Ionta, EPFL
Bogdan Draganski, Mirta Fiorio, Francois Vingerhoets.
"Cortical reorganization following behavioral treatment of focal dystonia"
Presentation type: Science
Gunther Helms, MR-Research in Neurology and Psychiatry, University Medical Center, Göttingen.
"MRI contrast and microstructure of brain tissue"
Why does MRI provide consistent contrast, if tissues feature a variable and complex “structure” at the cellular and histological scale? Some simple notions for a basic understanding of MRI contrast in human brain will be elaborated: fast exchange with MRI invisible macromolecular protons, the role of exchange, diffusion, and iron as an endogenous contrast agent. Particular emphasis is given to myelin, the major source of contrast in human brain. Interdependencies of contrast parameters are discussed based on normal brain, pathologies, and post mortem studies.
08 July 2011
Presentation type: Science
Armin Schnider, Dept. of Clinical Neurosciences, Division of Neurorehabilitation, University Hospitals of Geneva
"Human memory: from encoding to filtering"
Damage of the hippocampus disrupts the durable storage of information – encoding and consolidation fail. Damage of the orbitofrontal cortex may disrupt appropriate use of memories – reality filtering fails. How and when do these systems influence the processing of memories? And how do they interact? In this talk, evidence from clinical exploration and electrical imaging will be presented that indicates that (1) consolidation may be a much faster and shorter process than previously thought; (2) reality filtering occurs before the content of memories is consciously recognized.
15 July 2011
Presentation type: Science
Axel Lindner, NoD Lab, Neurobiology of Decision Making, Hertie-Institute for Clinical Brain Research,Tübingen
"A role of parietal and premotor action planning in decision making? Evidence from human fMRI"
A fundamental question in decision making relates to the way that the nervous system represents alternative choice options: do we decide between alternative goals or, alternatively, do we choose between alternative plans for goal-directed actions? While it might seem intuitive that we first decide and then plan a behavior, this serial model of choice is tackled by the idea that both the planning and the execution of a goal-directed action reflect important decision variables themselves. Different amounts of planning demands and effort in execution are often associated with alternative choice options and thus these variables should clearly contribute to cost-benefit calculations in decision making. Furthermore, action planning could assist decision making in that it helps to reduce decision space to those options that are viable.
In my presentation, I’ll provide preliminary support for a role of action planning in decision making. I’ll present three human fMRI experiments that demonstrate (i) that posterior parietal and premotor cortex can have representations of alternative plans for goal-directed actions, (ii) that such plans are present also in a “naturalistic” choice-context (namely the selection between images for a personalized photo-product, such as a photo-mug, a photo-t-shirt etc., which subjects received as an actual reward), and (iii) how action-plans are modulated by expected rewards and punishments.
09 September 2011
Presentation type: Science
Alexandre Croquelois , DNC-Neuroréhabilitation-CHUV
"Translational research: from mouse mutant HeCo to human cases"
Cortical malformations are a frequent etiology of intractable epilepsy and mental retardation. The mouse mutant HeCo arose spontaneously in our colony and a candidate gene was recently discovered. Screening of a human panel allowed to demonstrate mutations of the human homolog gene in three brothers with severe cortical malformations, mental ratardation and epilepsy.
Presentation type: Science
Elia Formisano, Department of Experimental Psychology, Universiteit Maastricht
"FMRI statistical pattern recognition and machine learning"
16 September 2011
Presentation type: Science
Kia Nobre, Department of Experimental Psychology, the University of Oxford.
"How memory shapes perception"
Previous investigations into the neural mechanisms that optimise perception according to task-relevance have largely focused on attentional biases directed by explicit cues, such as an arrow pointing to the likely location of a subsequent target stimulus. However, in everyday life, we rarely enjoy the benefit of explicit cues to guide our attention. More typically, we must rely on our own past experiences, stored in long-term memory, to build the predictions that shape perception for goal-directed behaviour. Recent research has started to reveal the neural systems and mechanisms by which memories help shape perception.
23 September 2011 :
No Brain Meeting (Lemanic annual meeting)
30 September 2011
Presentation type: Science
Rolando Grave de Peralta, Electrical Neuroimaging Group, Geneva University Hospital
"Electrical Neuroimaging Methods: Theory"
Determining the neural activity within each area of the brain from non-invasive EEG (MEG) scalp measurements implies solving an ill-posed inverse problem. In this talk, we introduce the inverse problem, the difficulties inherent to its solution and we briefly sketch some of the approaches that are more often used in the literature. We then discuss how the biophysical laws that govern the propagation of electromagnetic fields in biological tissue automatically constraint the range of possible solutions to the problem leading to a model termed ELECTRA. The main limitations common to all linear solutions are described to emphasize the importance of relying on temporal estimates rather than instantaneous inverse solution maps to minimize spurious effects introduced by the inversion procedures.
Presentation type: Science
Sara Gonzalez Andino, Electrical Neuroimaging Group, Geneva University Hospital
"Electrical Neuroimaging Methods: Practice"
In this talk, we illustrate how the solutions obtained under ELECTRA model in combination with the analysis of the temporal estimates are physiologically meaningful and informative about the underlying neural processes. A single clinical study in a patient diagnosed with “affective blindsight” is shown to illustrate how this approach is capable to reveal information hidden to other imaging techniques such as fMRI or ERPs. A comparison using pattern recognition techniques between intracranial recordings and ELECTRA estimates obtained during different cognitive tasks reveals that there is little loss in information by relying on such non-invasive measures when adequately analyzed and interpreted.
07 October 2011
Presentation type: Science
Alexandre Pouget, Department of Brain and Cognitive Sciences,University of Rochester, NY
"Probabilistic inferences in neural circuits: from insects to humans"
A wide range of seemingly unrelated behaviors can be formalized as instances of probabilistic inferences. This includes odor recognition, sensorimotor transformation, decision making, simple arithmetic and visual search, to name just a few. In all cases, the optimal solution involves a type of inference known as marginalization. We will show that, given the variability reported in neural responses, marginalization can be implemented in neural circuits through a nonlinearity known as quadratic divisive normalization. This approach makes very specific predictions for any task involving marginalization. We tested these predictions in the specific case of visual search and found that human subjects do behave near optimally. Moreover, we will show that a network with quadratic divisive normalization provides a tight fit to the human data. A similar approach can be used to obtain an approximate solution to intractable marginalizations such as the one involved in olfaction. This approximate solution maps very naturally onto the architecture of the olfactory system.
14 October 2011
Presentation type: Science
Roye Salomon, LNCO, Brain and Mind Institute, EPFL
" Global Functional Connectivity Deficits in Schizophrenia Depend on Behavioral State."
Schizophrenia is a devastating psychiatric illness characterized by deterioration of cognitive and emotional processing. It has been hypothesized that aberrant cortical connectivity is implicated in the disease (Friston, 1998), yet previous studies of functional connectivity (FC) in schizophrenia have shown mixed results (Garrity et al., 2007; Jafri et al., 2008; Lynall et al., 2010). We measured FC using fMRI in human schizophrenia patients and human healthy controls during two different tasks and a rest condition, and constructed a voxel-based global FC index. The results show robust differences between schizophrenia and healthy subjects and that these differences are dependent on the behavioral state of the subject. This novel finding may shed light on the conflicting results previously found for FC in schizophrenia.
Presentation type: Project
Antonia Thelen and Micah Murray, CHUV
" When auditory events are neglected: An electrical neuroimaging study of the Colavita visual dominance effect. "
The Colavita visual dominance effect (Colavita, 1974) describes the neglecting of non-visual information on multisensory trials when subjects are instructed to press response buttons to both constituent unisensory events. This occurs despite being able to reliably detect/report all sensory modalities presented alone. As such, this paradigm constitutes on the one hand an intriguing example of multisensory interactions either not occurring or perhaps that are deleterious for perception/behavior. On the other hand, this paradigm may likewise provide insights on the mechanisms of neglect and extinction. To date, there are no hemodynamic or electrical brain imaging data regarding this effect. This Project Presentations will be constructed as follows: 1. Theoretical Background 2. Hypotheses 3. Experimental Design 4. Statistical Analyses.
21 October 2011
Presentation type: Science
TBA
28 October 2011
Presentation type: Science
Karl Friston, Wellcome Trust Centre for Neuroimaging, UCL
" Free energy and affordance "
In this presentation, I will rehearse the free-energy formulation of action and perception, with a special focus on the representation of uncertainty: The free-energy principle is based upon the notion that both action and perception are trying to minimise the surprise (prediction error) associated with sensory input. In this scheme, perception is the process of optimising sensory predictions by adjusting internal brain states and connections; while action is regarded as an adaptive sampling of sensory input to ensure it conforms to perceptual predictions (this is known as active inference). Both action and perception rest on an optimum representation of uncertainty, which corresponds to the precision of prediction error. Neurobiologically, this may be encoded by the postsynaptic gain of prediction error units. I hope to illustrate the plausibility of this framework using simple simulations of cued, sequential, movements. Crucially, the predictions driving movements are based upon a hierarchical generative model that infers the context in which movements are made. This means that we can temporarily confuse agents by changing the context (order) in which cues are presented. These simulations provide a (Bayes-optimal) simulation of contextual uncertainty and set-switching that can be characterised in terms of behaviour and electrophysiological responses. Interestingly, one can lesion the encoding of precision (postsynaptic gain) to produce pathological behaviours that are reminiscent of those seen in Parkinson's disease. I will use this as a toy example of how information theoretic approaches to uncertainty may help understand action selection, affordance and set-switching.
