The Experts below are selected from a list of 18681 Experts worldwide ranked by ideXlab platform
Matti Hamalainen - One of the best experts on this subject based on the ideXlab platform.
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Magnetoencephalography signal processing forward modeling Magnetoencephalography inverse source imaging and coherence analysis
Neuroimaging Clinics of North America, 2020Co-Authors: Matti Hamalainen, Mingxiong Huang, Susan M BowyerAbstract:: Magnetoencephalography (MEG) is a noninvasive functional imaging technique for the brain. MEG directly measures the magnetic signal due to neuronal activation in gray matter with high spatial localization accuracy. The first part of this article covers the overall concepts of MEG and the forward and inverse modeling techniques. It is followed by examples of analyzing evoked and resting-state MEG signals using a high-resolution MEG source imaging technique. Next, different techniques for connectivity and network analysis are reviewed with examples showing connectivity estimates from resting-state and epileptic activity.
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detectability of cerebellar activity with Magnetoencephalography and electroencephalography
Human Brain Mapping, 2020Co-Authors: Sheraz Khan, John G Samuelsson, Padmavathi Sundaram, Martin I Sereno, Matti HamalainenAbstract:Electrophysiological signals from the cerebellum have traditionally been viewed as inaccessible to Magnetoencephalography (MEG) and electroencephalography (EEG). Here, we challenge this position by investigating the ability of MEG and EEG to detect cerebellar activity using a model that employs a high-resolution tessellation of the cerebellar cortex. The tessellation was constructed from repetitive high-field (9.4T) structural magnetic resonance imaging (MRI) of an ex vivo human cerebellum. A boundary-element forward model was then used to simulate the M/EEG signals resulting from neural activity in the cerebellar cortex. Despite significant signal cancelation due to the highly convoluted cerebellar cortex, we found that the cerebellar signal was on average only 30-60% weaker than the cortical signal. We also made detailed M/EEG sensitivity maps and found that MEG and EEG have highly complementary sensitivity distributions over the cerebellar cortex. Based on previous fMRI studies combined with our M/EEG sensitivity maps, we discuss experimental paradigms that are likely to offer high M/EEG sensitivity to cerebellar activity. Taken together, these results show that cerebellar activity should be clearly detectable by current M/EEG systems with an appropriate experimental setup.
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ifcn endorsed practical guidelines for clinical Magnetoencephalography meg
Clinical Neurophysiology, 2018Co-Authors: Riitta Hari, Gareth R. Barnes, Matti Hamalainen, Sylvain Baillet, Ole Jensen, Richard Burgess, Nina Forss, Joachim Gross, Ryusuke Kakigi, F. MauguièreAbstract:Magnetoencephalography (MEG) records weak magnetic fields outside the human head and thereby provides millisecond-accurate information about neuronal currents supporting human brain function. MEG and electroencephalography (EEG) are closely related complementary methods and should be interpreted together whenever possible. This manuscript covers the basic physical and physiological principles of MEG and discusses the main aspects of state-of-the-art MEG data analysis. We provide guidelines for best practices of patient preparation, stimulus presentation, MEG data collection and analysis, as well as for MEG interpretation in routine clinical examinations. In 2017, about 200 whole-scalp MEG devices were in operation worldwide, many of them located in clinical environments. Yet, the established clinical indications for MEG examinations remain few, mainly restricted to the diagnostics of epilepsy and to preoperative functional evaluation of neurosurgical patients. We are confident that the extensive ongoing basic MEG research indicates potential for the evaluation of neurological and psychiatric syndromes, developmental disorders, and the integrity of cortical brain networks after stroke. Basic and clinical research is, thus, paving way for new clinical applications to be identified by an increasing number of practitioners of MEG.
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somatosensory cortex functional connectivity abnormalities in autism show opposite trends depending on direction and spatial scale
Brain, 2015Co-Authors: Sheraz Khan, Konstantinos P Michmizos, Mark Tommerdahl, Santosh Ganesan, Manfred G Kitzbichler, Manuel Zetino, Keri Lee A Garel, Martha R Herbert, Matti HamalainenAbstract:Functional connectivity is abnormal in autism, but the nature of these abnormalities remains elusive. Different studies, mostly using functional magnetic resonance imaging, have found increased, decreased, or even mixed pattern functional connectivity abnormalities in autism, but no unifying framework has emerged to date. We measured functional connectivity in individuals with autism and in controls using Magnetoencephalography, which allowed us to resolve both the directionality (feedforward versus feedback) and spatial scale (local or long-range) of functional connectivity. Specifically, we measured the cortical response and functional connectivity during a passive 25-Hz vibrotactile stimulation in the somatosensory cortex of 20 typically developing individuals and 15 individuals with autism, all males and right-handed, aged 8–18, and the mu-rhythm during resting state in a subset of these participants (12 per group, same age range). Two major significant group differences emerged in the response to the vibrotactile stimulus. First, the 50-Hz phase locking component of the cortical response, generated locally in the primary (S1) and secondary (S2) somatosensory cortex, was reduced in the autism group ( P < 0.003, corrected). Second, feedforward functional connectivity between S1 and S2 was increased in the autism group ( P < 0.004, corrected). During resting state, there was no group difference in the mu-α rhythm. In contrast, the mu-β rhythm, which has been associated with feedback connectivity, was significantly reduced in the autism group ( P < 0.04, corrected). Furthermore, the strength of the mu-β was correlated to the relative strength of 50 Hz component of the response to the vibrotactile stimulus (r = 0.78, P < 0.00005), indicating a shared aetiology for these seemingly unrelated abnormalities. These Magnetoencephalography-derived measures were correlated with two different behavioural sensory processing scores ( P < 0.01 and P < 0.02 for the autism group, P < 0.01 and P < 0.0001 for the typical group), with autism severity ( P < 0.03), and with diagnosis (89% accuracy). A biophysically realistic computational model using data driven feedforward and feedback parameters replicated the Magnetoencephalography data faithfully. The direct observation of both abnormally increased and abnormally decreased functional connectivity in autism occurring simultaneously in different functional connectivity streams, offers a potential unifying framework for the unexplained discrepancies in current findings. Given that cortical feedback, whether local or long-range, is intrinsically non-linear, while cortical feedforward is generally linear relative to the stimulus, the present results suggest decreased non-linearity alongside an increased veridical component of the cortical response in autism. * Abbreviations : ADOS : Autism Diagnostic Observation Schedule ASD : autism spectrum disorder LFCi : local functional connectivity index MEG : Magnetoencephalography
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language lateralization represented by spatiotemporal mapping of Magnetoencephalography
American Journal of Neuroradiology, 2013Co-Authors: Naoaki Tanaka, Matti Hamalainen, Claus Reinsberger, Joseph R Madsen, Blaise F D Bourgeois, Barbara A Dworetzky, Steven M StufflebeamAbstract:BACKGROUND AND PURPOSE: Determination of hemispheric language dominance is critical for planning epilepsy surgery. We assess the usefulness of spatiotemporal source analysis of Magnetoencephalography for determining language laterality. MATERIALS AND METHODS: Thirty-five patients with epilepsy were studied. The patients performed a semantic word-processing task during MEG recording. Epochs containing language-related neuromagnetic activity were averaged after preprocessing. The averaged data between 250 and 550 ms after stimulus were analyzed by using dynamic statistical parametric mapping. ROIs were obtained in the opercular and triangular parts of the inferior frontal gyrus, superior temporal gyrus, and supramarginal gyrus in both hemispheres. We calculated laterality indices according to 1) dSPM-amplitude method, based on the amplitude of activation in the ROIs, and 2) dSPM-counting method, based on the number of unit dipoles with activation over a threshold in the ROIs. The threshold was determined as half of the maximum value in all ROIs for each patient. A LI ≥0.10 or ≤−0.10 was considered left- or right-hemisphere dominance, respectively; a LI between −0.10 and 0.10 was considered bilateral. All patients underwent an intracarotid amobarbital procedure as part of presurgical evaluation. RESULTS: The dSPM-counting method demonstrated laterality consistent with the IAP in 32 of 35 patients (91.4%), the remaining 3 (8.6%) demonstrated bilateral language representation, whereas the dSPM-amplitude method showed 18 (51.4%) concordant and 17 (48.6%) bilateral. No laterality opposite to the IAP was found. CONCLUSIONS: Spatiotemporal mapping of language lateralization with the dSPM-counting method may reduce the necessity for an IAP in as many as 90% of patients.
Riitta Hari - One of the best experts on this subject based on the ideXlab platform.
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ifcn endorsed practical guidelines for clinical Magnetoencephalography meg
Clinical Neurophysiology, 2018Co-Authors: Riitta Hari, Gareth R. Barnes, Matti Hamalainen, Sylvain Baillet, Ole Jensen, Richard Burgess, Nina Forss, Joachim Gross, Ryusuke Kakigi, F. MauguièreAbstract:Magnetoencephalography (MEG) records weak magnetic fields outside the human head and thereby provides millisecond-accurate information about neuronal currents supporting human brain function. MEG and electroencephalography (EEG) are closely related complementary methods and should be interpreted together whenever possible. This manuscript covers the basic physical and physiological principles of MEG and discusses the main aspects of state-of-the-art MEG data analysis. We provide guidelines for best practices of patient preparation, stimulus presentation, MEG data collection and analysis, as well as for MEG interpretation in routine clinical examinations. In 2017, about 200 whole-scalp MEG devices were in operation worldwide, many of them located in clinical environments. Yet, the established clinical indications for MEG examinations remain few, mainly restricted to the diagnostics of epilepsy and to preoperative functional evaluation of neurosurgical patients. We are confident that the extensive ongoing basic MEG research indicates potential for the evaluation of neurological and psychiatric syndromes, developmental disorders, and the integrity of cortical brain networks after stroke. Basic and clinical research is, thus, paving way for new clinical applications to be identified by an increasing number of practitioners of MEG.
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Magnetoencephalography in the study of human somatosensory cortical processing
Philosophical Transactions of the Royal Society B, 1999Co-Authors: Riitta Hari, Nina ForssAbstract:Magnetoencephalography (MEG) is a totally non-invasive research method which provides information about cortical dynamics on a millisecond time-scale. Whole-scalp magnetic field patterns following stimulation of different peripheral nerves indicate activation of an extensive cortical network. At the SI cortex, the responses reflect mainly the activity of area 3b, with clearly somatotopical representations of different body parts. The SII cortex is activated bilaterally and it also receives, besides tactile input, nociceptive afference. Somatically evoked MEG signals may also be detected from the posterior parietal cortex, central mesial cortex and the frontal lobe. The serial versus parallel processing in the cortical somatosensory network is still under debate.
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information processing in the human brain magnetoencephalographic approach
Proceedings of the National Academy of Sciences of the United States of America, 1996Co-Authors: O V Lounasmaa, Matti Hamalainen, Riitta Hari, Riitta SalmelinAbstract:Abstract Rapid progress in effective methods to image brain functions has revolutionized neuroscience. It is now possible to study noninvasively in humans neural processes that were previously only accessible in experimental animals and in brain-injured patients. In this endeavor, positron emission tomography has been the leader, but the superconducting quantum interference device-based Magnetoencephalography (MEG) is gaining a firm role, too. With the advent of instruments covering the whole scalp, MEG, typically with 5-mm spatial and 1-ms temporal resolution, allows neuroscientists to track cortical functions accurately in time and space. We present five representative examples of recent MEG studies in our laboratory that demonstrate the usefulness of whole-head Magnetoencephalography in investigations of spatiotemporal dynamics of cortical signal processing.
M Russo - One of the best experts on this subject based on the ideXlab platform.
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multichannel system based on a high sensitivity superconductive sensor for Magnetoencephalography
Sensors, 2014Co-Authors: Sara Rombetto, Carmine Granata, Antonio Vettoliere, M RussoAbstract:We developed a multichannel system based on superconducting quantum interference devices (SQUIDs) for Magnetoencephalography measurements. Our system consists of 163 fully-integrated SQUID magnetometers, 154 channels and 9 references, and all of the operations are performed inside a magnetically-shielded room. The system exhibits a magnetic field noise spectral density of approximatively 5 fT/Hz1/2. The presented Magnetoencephalography is the first system working in a clinical environment in Italy.
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squid based multichannel system for Magnetoencephalography
arXiv: Medical Physics, 2013Co-Authors: Sara Rombetto, Carmine Granata, Antonio Vettoliere, A Trebeschi, R Rossi, M RussoAbstract:Here we present a multichannel system based on superconducting quantum interference devices (SQUIDs) for Magnetoencephalography (MEG) measurements, developed and installed at Istituto di Cibernetica (ICIB) in Naples. This MEG system, consists of 163 full integrated SQUID magnetometers, 154 channels and 9 references, and has been designed to meet specifications concerning noise, dynamic range, slew rate and linearity through optimized design. The control electronics is located at room temperature and all the operations are performed inside a Magnetically Shielded Room (MSR). The system exhibits a magnetic white noise level of approximatively 5 fT/Hz1=2. This MEG system will be employed for both clinical and routine use. PACS numbers: 74.81.Fa, 85.25.Hv, 07.20.Mc, 85.25.Dq, 87.19.le, 87.85.Ng
N Focke - One of the best experts on this subject based on the ideXlab platform.
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reliability of Magnetoencephalography and high density electroencephalography resting state functional connectivity metrics
Brain, 2019Co-Authors: Justus Marquetand, Silvia Vannoni, Margherita Carboni, Yiwen Li Hegner, Christina Stier, Christoph Braun, N FockeAbstract:Abstract Resting-state connectivity, for example, based on Magnetoencephalography (MEG) or electroencephalography (EEG), is a widely used method for characterizing brain networks and a promising im...
Carmine Granata - One of the best experts on this subject based on the ideXlab platform.
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Magnetoencephalography system based on quantum magnetic sensors for clinical applications
Sensors, 2018Co-Authors: Carmine Granata, Oliviero Talamo, Rosaria Rucco, Pier Paolo Sorrentino, Francesca Jacini, Marianna Liparoti, Fabio Baselice, Antonio Vettoliere, Paolo Silvestrini, Anna LardoneAbstract:In this paper, we present the Magnetoencephalography system developed by the Institute of Applied Sciences and Intelligent Systems of the National Research Council and recently installed in a clinical environment. The system employ ultra high sensitive magnetic sensors based on superconducting quantum interference devices (SQUIDs). SQUID sensors have been realized using a standard trilayer technology that ensures good performances over time and a good signal-to-noise ratio, even at low frequencies. They exhibit a spectral density of magnetic field noise as low as 2 fT/Hz1/2. Our system consists of 163 fully-integrated SQUID magnetometers, 154 channels and 9 references, and all of the operations are performed inside a magnetically-shielded room having a shielding factor of 56 dB at 1 Hz. Preliminary measurement have demonstrated the effectiveness of the MEG system to perform useful measurements for clinical and neuroscience investigations. Such a Magnetoencephalography is the first system working in a clinical environment in Italy.
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multichannel system based on a high sensitivity superconductive sensor for Magnetoencephalography
Sensors, 2014Co-Authors: Sara Rombetto, Carmine Granata, Antonio Vettoliere, M RussoAbstract:We developed a multichannel system based on superconducting quantum interference devices (SQUIDs) for Magnetoencephalography measurements. Our system consists of 163 fully-integrated SQUID magnetometers, 154 channels and 9 references, and all of the operations are performed inside a magnetically-shielded room. The system exhibits a magnetic field noise spectral density of approximatively 5 fT/Hz1/2. The presented Magnetoencephalography is the first system working in a clinical environment in Italy.
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squid based multichannel system for Magnetoencephalography
arXiv: Medical Physics, 2013Co-Authors: Sara Rombetto, Carmine Granata, Antonio Vettoliere, A Trebeschi, R Rossi, M RussoAbstract:Here we present a multichannel system based on superconducting quantum interference devices (SQUIDs) for Magnetoencephalography (MEG) measurements, developed and installed at Istituto di Cibernetica (ICIB) in Naples. This MEG system, consists of 163 full integrated SQUID magnetometers, 154 channels and 9 references, and has been designed to meet specifications concerning noise, dynamic range, slew rate and linearity through optimized design. The control electronics is located at room temperature and all the operations are performed inside a Magnetically Shielded Room (MSR). The system exhibits a magnetic white noise level of approximatively 5 fT/Hz1=2. This MEG system will be employed for both clinical and routine use. PACS numbers: 74.81.Fa, 85.25.Hv, 07.20.Mc, 85.25.Dq, 87.19.le, 87.85.Ng
