1,721,546 research outputs found
Simultaneous recording of EEG and BOLD responses: a historical perspective
No full textElectromagnetic fields as measured with electroencephalogram (EEG) are a direct consequence of neuronal activity and feature the same timescale as the underlying cognitive processes, while hemodynamic signals as measured with functional magnetic resonance imaging (fMRI) are related to the energy consumption of neuronal populations. It is obvious that a combination of both techniques is a very attractive aim in neuroscience, in order to achieve both high temporal and spatial resolution for the non-invasive study of cognitive brain function. During the last decade a number of research groups have taken up this challenge. Here, we review the development of the combined EEG-fMRI approach. We summarize the main data integration approaches developed to achieve such a combination, discuss the current state-of-the-art in this field and outline challenges for the future success of this promising approac
Editorial. Integration of EEG and fMRI
No full textThe combination of electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) provides us with the opportunity to study human brain function non-invasively with high temporal and spatial resolution. Over the past few years, many experts have addressed problems in the field of EEG–fMRI integration, and substantial progress has been made. However, among the persisting challenges is the question of how simultaneously to collect good quality EEG and fMRI data. Furthermore, the problem of recovering a reasonable EEG signal quality from simultaneous recordings is not yet solved. Finally, the most fundamental problem probably relates to the question of how statistically to integrate EEG and fMRI signals. The articles published in this special issue reflect the current state of research in this rapidly evolving area and provide new insights that help to address these problems.Pioneering efforts regarding the integration of separately recorded neuroimaging and event-related potential (ERP) data date back more than 20 years. Herrmann and Debener summarize the progress made from the first truly simultaneous recording of EEG–fMRI data to the current standard. Today, there exist specifically designed commercially available EEG systems that facilitate the collection of high-density EEG recordings inside the MRI scanner.Yet, MRI laboratories are certainly not EEG-friendly environments, and inside scanner EEG recordings suffer from artefacts that can easily be several orders of magnitude larger than the outside scanner EEG signal. The article of Warbrick et al. is concerned with practical aspects related to simultaneous EEG–fMRI recordings. Specifically, the authors examined how different MRI scanning strategies, in combination with different artefact removal procedures, affect the resulting quality of visual evoked potentials. The authors conclude that EEG recordings require minimal changes to the fMRI acquisition protocol.The issue of compromised data quality is also addressed by the following two papers. Importantly, Mullinger et al. examined the impact of EEG electrodes and cables on MRI image quality, an issue that has been largely neglected so far. The results indicate that the EEG setup does not result in a dramatic reduction of the MRI image quality. Debener et al. studied the properties of the ballistocardiogram, an artefact that clearly compromises the quality of EEG signals recorded inside the MRI. A model addressing the origin of the ballistocardiogram is presented, aiming to explain the spatial and temporal dynamics of this artefact. This in turn may help to further optimize ballistocardiogram removal techniques.The following articles address the question of how to combine and integrate EEG and fMRI signals. Wibral and colleagues compared the usage of independent component analysis (ICA) for evoked potential research with fMRI-informed dipole seeding, a technique that can be used for the combination of separately recorded EEG and fMRI data. Eichele et al. and Moosmann et al. specifically explored ways of directly integrating EEG–fMRI signals. Importantly, these two studies consider EEG and fMRI signals on a single-trial level, which enables the investigation of a possible coupling between EEG and the fMRI blood oxygenation level dependent (BOLD) signal. It is remarkable that all three papers that are concerned with EEG–fMRI integration consider ICA as an important signal processing tool. Indeed, ICA has been shown to be a powerful tool for the processing of EEG and fMRI signals, and seems extremely helpful for the integration of both measures.The last group of papers addresses more practical research questions. Using a silent fMRI acquisition technique, Thaerig et al. found that a well known auditory evoked potential amplitude manipulation, namely the N100 amplitude increase with loudness, can be obtained from inside scanner EEG recordings. By application of the EEG-informed fMRI analysis approach, Scheeringa et al. for the first time provide evidence for a direct link between EEG activity in the theta frequency range and regionally circumscribed fMRI BOLD activity. Interestingly, the identified network of brain areas coupled to theta activity is known as the default mode brain system. This work, and that of Eichele et al., in particular demonstrate the added value of direct EEG–fMRI integration, as they show that both measures provide information beyond that which can be achieved by either technique alone. And finally, Khader and colleagues review the available evidence for a close correspondence between slow potentials of the EEG and fMRI BOLD signals. While it is not yet known which EEG signals do, and which do not, correspond to the fMRI BOLD signal, this paper highlights the importance of exploring EEG–fMRI integration from different angles.The special issue is an expansion of the symposium “Multimodal Imaging: Integration of EEG and fMRI data”, presented at the 32nd German Congress on Psychology and the Brain, held in Dresden, Germany in 2006. Several of the papers were also presented at the 13th Annual Meeting of the Organization for Human Brain Mapping in Chicago, Illinois, 2007. We would like to thank Dr. John Andreassi, editor of the International Journal of Psychophysiology, for supporting us in compiling this special issue. The people that provided the most direct support are the reviewers. We are very grateful for their service
Transcranial Alternating Current and Random Noise Stimulation: Possible Mechanisms
Full text linkBackground. Transcranial alternating current stimulation (tACS) is a relatively recent method suited to noninvasively modulate brain oscillations. Technically the method is similar but not identical to transcranial direct current stimulation (tDCS). While decades of research in animals and humans has revealed the main physiological mechanisms of tDCS, less is known about the physiological mechanisms of tACS. Method. Here, we review recent interdisciplinary research that has furthered our understanding of how tACS affects brain oscillations and by what means transcranial random noise stimulation (tRNS) that is a special form of tACS can modulate cortical functions. Results. Animal experiments have demonstrated in what way neurons react to invasively and transcranially applied alternating currents. Such findings are further supported by neural network simulations and knowledge from physics on entraining physical oscillators in the human brain. As a result, fine-grained models of the human skull and brain allow the prediction of the exact pattern of current flow during tDCS and tACS. Finally, recent studies on human physiology and behavior complete the picture of noninvasive modulation of brain oscillations. Conclusion. In future, the methods may be applicable in therapy of neurological and psychiatric disorders that are due to malfunctioning brain oscillations
The economics of European monetary integration
No full textPresenting a sweeping analysis of the legal foundations, institutions, and substantive legal issues in EU monetary integration, The EU Law of Economic and Monetary Union serves as an authoritative reference on the legal framework of European economic and monetary union
EEG gamma-band activity in rapid serial visual presentation
No full textEvidence is available that oscillatory activity in the gamma frequency range (>30 Hz) might be related to the attentional selection of target items. Rapid serial visual presentation (RSVP) paradigms are instrumental in addressing cognitive functions such as visual attention, and they are increasingly combined with the measurement of electrical brain activity. In the present study, gamma-band responses for target and standard stimuli were investigated in an RSVP oddball paradigm. In a first study, stimuli were presented at a frequency of 10 Hz, the stimulus sequence consisted of rare colored letters (targets) and frequent black letters (standards). In addition, stimulus size was varied across experimental blocks. Significant target modulations were observed for the P3 ERP and induced (i.e., not phase-locked) gamma-band responses. Besides this late activation, no further gamma-band responses were observed. A second study aimed at replicating these findings by employing a reduced stimulus presentation rate of 7.1 Hz. Again, besides the P3 ERP a late increase in induced gamma-band activity was observed. However, as compared to Study 1, this induced response was less pronounced. The induced gamma-band response observed in the present studies might reflect utilization of information derived from previous processing steps for behavioral performance or memory storage as suggested in the ‘match-and-utilization-model’ of gamma activity
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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