918 research outputs found
Causal hierarchy within the thalamo-cortical network in spike and wave discharges
No full textBackground: Generalised spike wave (GSW) discharges are the electroencephalographic (EEG) hallmark of absence seizures, clinically characterised by a transitory interruption of ongoing activities and impaired consciousness, occurring during states of reduced awareness. Several theories have been proposed to explain the pathophysiology of GSW discharges and the role of thalamus and cortex as generators. In this work we extend the existing theories by hypothesizing a role for the precuneus, a brain region neglected in previous works on GSW generation but already known to be linked to consciousness and awareness. We analysed fMRI data using dynamic causal modelling (DCM) to investigate the effective connectivity between precuneus, thalamus and prefrontal cortex in patients with GSW discharges. Methodology and Principal Findings: We analysed fMRI data from seven patients affected by Idiopathic Generalized Epilepsy (IGE) with frequent GSW discharges and significant GSW-correlated haemodynamic signal changes in the thalamus, the prefrontal cortex and the precuneus. Using DCM we assessed their effective connectivity, i.e. which region drives another region. Three dynamic causal models were constructed: GSW was modelled as autonomous input to the thalamus (model A), ventromedial prefrontal cortex (model B), and precuneus (model C). Bayesian model comparison revealed Model C (GSW as autonomous input to precuneus), to be the best in 5 patients while model A prevailed in two cases. At the group level model C dominated and at the population-level the p value of model C was ∼1. Conclusion: Our results provide strong evidence that activity in the precuneus gates GSW discharges in the thalamo-(fronto) cortical network. This study is the first demonstration of a causal link between haemodynamic changes in the precuneus - an index of awareness - and the occurrence of pathological discharges in epilepsy. © 2009 Vaudano et al
Mutual information identifies spurious Hurst phenomena in resting state EEG and fMRI data
No full textLong-range memory in time series is often quantified by the Hurst exponent H, a measure of the signal's variance across several time scales. We analyze neurophysiological time series from electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) resting state experiments with two standard Hurst exponent estimators and with the time-lagged mutual information function applied to discretized versions of the signals. A confidence interval for the mutual information function is obtained from surrogate Markov processes with equilibrium distribution and transition matrix identical to the underlying signal. For EEG signals, we construct an additional mutual information confidence interval from a short-range correlated, tenth-order autoregressive model. We reproduce the previously described Hurst phenomenon (H>0.5) in the analytical amplitude of alpha frequency band oscillations, in EEG microstate sequences, and in fMRI signals, but we show that the Hurst phenomenon occurs without long-range memory in the information-theoretical sense. We find that the mutual information function of neurophysiological data behaves differently from fractional Gaussian noise (fGn), for which the Hurst phenomenon is a sufficient condition to prove long-range memory. Two other well-characterized, short-range correlated stochastic processes (Ornstein-Uhlenbeck, Cox-Ingersoll-Ross) also yield H>0.5, whereas their mutual information functions lie within the Markovian confidence intervals, similar to neural signals. In these processes, which do not have long-range memory by construction, a spurious Hurst phenomenon occurs due to slow relaxation times and heteroscedasticity (time-varying conditional variance). In summary, we find that mutual information correctly distinguishes long-range from short-range dependence in the theoretical and experimental cases discussed. Our results also suggest that the stationary fGn process is not sufficient to describe neural data, which seem to belong to a more general class of stochastic processes, in which multiscale variance effects produce Hurst phenomena without long-range dependence. In our experimental data, the Hurst phenomenon and long-range memory appear as different system properties that should be estimated and interpreted independently.Fil: Von Wegner, Frederic. Goethe Universitat Frankfurt; AlemaniaFil: Laufs, Helmut. University Hospital Kiel; Alemania. Goethe Universitat Frankfurt; AlemaniaFil: Tagliazucchi, Enzo Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Goethe Universitat Frankfurt; Alemani
From Helmut Jürgensen’s former students: The game of informatics
No full textPersonal reflections are given on being students of Helmut Jürgensen. Then, we attempt
to address his hypothesis that informatics follows trend-like behaviours through the
use of a content analysis of university job advertisements, and then via simulation
techniques from the area of quantitative economics
Smalltalk Interpreter in Java
No full textAuthor Helmut Rohregger, BSc.Kurzfassungen in deutscher und englischer SpracheMasterarbeit Universität Linz 201
Smalltalk Interpreter in Java
No full textAuthor Helmut Rohregger, BSc.Kurzfassungen in deutscher und englischer SpracheMasterarbeit Universität Linz 201
HELMUT E. LUCK JAKO HISTORYK PSYCHOLOGII
No full textThe article presents the figure of Helmut E. Luck, well-known scientist in the world of historians of psychology. Helmut E. Luck also is well-known in Poland, as the author or the scientific editor of several books in the field of history of psychology. In the first part of the article the short presentation of his scientific career and his scientific achievements are demonstrated. The second part comprises the analysis of his opinions in the scope of social psychology. Helmut E. Luck was the one of pioneers in psychology, who paid attention to social positive phenomena or social positive behaviors. In the field of history of psychology, H.E.Luck made the contribution to methodological analysis of psychological ideas in history, preferring the model which underlines connection of psychology with culture and at the same time creates the opportunity to analysis of biographical plots. The article also shows unquestionable and unusually merits of Luck’s in popularization of knowledge about history of psychology.The article presents the figure of Helmut E. Luck, well-known scientist in the world of historians of psychology. Helmut E. Luck also is well-known in Poland, as the author or the scientific editor of several books in the field of history of psychology. In the first part of the article the short presentation of his scientific career and his scientific achievements are demonstrated. The second part comprises the analysis of his opinions in the scope of social psychology. Helmut E. Luck was the one of pioneers in psychology, who paid attention to social positive phenomena or social positive behaviors. In the field of history of psychology, H.E.Luck made the contribution to methodological analysis of psychological ideas in history, preferring the model which underlines connection of psychology with culture and at the same time creates the opportunity to analysis of biographical plots. The article also shows unquestionable and unusually merits of Luck’s in popularization of knowledge about history of psychology
Human non-REM sleep and the mean global BOLD signal
No full textA hallmark of non-rapid eye movement (REM) sleep is the decreased brain activity as measured by global reductions in cerebral blood flow, oxygen metabolism, and glucose metabolism. It is unknown whether the blood oxygen level dependent (BOLD) signal undergoes similar changes. Here we show that, in contrast to the decreases in blood flow and metabolism, the mean global BOLD signal increases with sleep depth in a regionally non-uniform manner throughout gray matter. We relate our findings to the circulatory and metabolic processes influencing the BOLD signal and conclude that because oxygen consumption decreases proportionately more than blood flow in sleep, the resulting decrease in paramagnetic deoxyhemoglobin accounts for the increase in mean global BOLD signal.Fil: McAvoy, Mark P.. Washington University in St. Louis; Estados UnidosFil: Tagliazucchi, Enzo Rodolfo. Institut du Cerveau et de la Moelle épinière; Francia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Laufs, Helmut. Christian-albrechts-universität Zu Kiel; . Goethe Universitat Frankfurt; AlemaniaFil: Raichle, Marcus E.. Washington University in St. Louis; Estados Unido
Die IPrA, Helmut und ich
No full textThis contribution describes the beginning and the development of the professional and personal relationship between Helmut and the author which has been highly influenced by our joint membership in the International Pragmatics Association and by our activities in and for the IPrA
Helmut E. Luck and history of psychology
No full textThe article presents the figure of Helmut E. Luck, well-known scientist in the world of historians of psychology. Helmut E. Luck also is well-known in Poland, as the author or the scientific editor of several books in the field of history of psychology. In the first part of the article the short presentation of his scientific career and his scientific achievements are demonstrated. The second part comprises the analysis of his opinions in the scope of social psychology. Helmut E. Luck was the one of pioneers in psychology, who paid attention to social positive phenomena or social positive behaviors. In the field of history of psychology, H.E.Luck made the contribution to methodological analysis of psychological ideas in history, preferring the model which underlines connection of psychology with culture and at the same time creates the opportunity to analysis of biographical plots. The article also shows unquestionable and unusually merits of Luck’s in popularization of knowledge about history of psychology
The Voxel-Wise Functional Connectome Can Be Efficiently Derived from Co-activations in a Sparse Spatio-Temporal Point-Process
No full textLarge efforts are currently under way to systematically map functional connectivity between all pairs of millimeter-scale brain regions based on large neuroimaging databases. The exploratory unraveling of this "functional connectome" based on functional Magnetic Resonance Imaging (fMRI) can benefit from a better understanding of the contributors to resting state functional connectivity. In this work, we introduce a sparse representation of fMRI data in the form of a discrete point-process encoding high-amplitude events in the blood oxygenation level-dependent (BOLD) signal and we show it contains sufficient information for the estimation of functional connectivity between all pairs of voxels. We validate this method by replicating results obtained with standard whole-brain voxel-wise linear correlation matrices in two datasets. In the first one (n = 71), we study the changes in node strength (a measure of network centrality) during deep sleep. The second is a large database (n = 1147) of subjects in which we look at the age-related reorganization of the voxel-wise network of functional connections. In both cases it is shown that the proposed method compares well with standard techniques, despite requiring only data on the order of 1% of the original BOLD signal time series. Furthermore, we establish that the point-process approach does not reduce (and in one case increases) classification accuracy compared to standard linear correlations. Our results show how large fMRI datasets can be drastically simplified to include only the timings of large-amplitude events, while still allowing the recovery of all pair-wise interactions between voxels. The practical importance of this dimensionality reduction is manifest in the increasing number of collaborative efforts aiming to study large cohorts of healthy subjects as well as patients suffering from brain disease. Our method also suggests that the electrophysiological signals underlying the dynamics of fMRI time series consist of all-or-none temporally localized events, analogous to the avalanches of neural activity observed in recordings of local field potentials (LFP), an observation of potentially high neurobiological relevance.Fil: Tagliazucchi, Enzo. Christian Albrechts Universitat Zu Kiel.; Alemania. University Frankfurt am Main; AlemaniaFil: Siniatchkin, Michael. Christian Albrechts Universitat Zu Kiel.; AlemaniaFil: Laufs, Helmut. University Frankfurt am Main; Alemania. University Hospital Schleswig Holstein; AlemaniaFil: Chialvo, Dante Renato. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martin. Escuela de Ciencia y Tecnologia. Centro de Estudios Multidisciplinarios En Sistemas Complejos y Ciencias del Cerebro.; Argentin
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