IFCN-endorsed practical guidelines for clinical magnetoencephalography (MEG)

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. (C) 2018 International Federation of Clinical Neurophysiology. Published by Elsevier B.V.Peer reviewe

Cortical mechanisms of seeing and hearing speech

In face-to-face communication speech is perceived through eyes and ears. The talker's articulatory gestures are seen and the speech sounds are heard simultaneously. Whilst acoustic speech can be often understood without visual information, viewing articulatory gestures aids hearing substantially in noisy conditions. On the other hand, speech can be understood, to some extent, by solely viewing articulatory gestures (i.e., by speechreading). In this thesis, electroencephalography (EEG), magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI) were utilized to disclose cortical mechanisms of seeing and hearing speech. One of the major challenges of modern cognitive neuroscience is to find out how the brain integrates inputs from different senses. In this thesis, integration of seen and heard speech was investigated using EEG and MEG. Multisensory interactions were found in the sensory-specific cortices at early latencies and in the multisensory regions at late latencies. Viewing other person's actions activate regions belonging to the human mirror neuron system (MNS) which are also activated when subjects themselves perform actions. Possibly, the human MNS enables simulation of other person's actions, which might be important also for speech recognition. In this thesis, it was demonstrated with MEG that seeing speech modulates activity in the mouth region of the primary somatosensory cortex (SI), suggesting that also the SI cortex is involved in simulation of other person's articulatory gestures during speechreading. The question whether there are speech-specific mechanisms in the human brain has been under scientific debate for decades. In this thesis, evidence for the speech-specific neural substrate in the left posterior superior temporal sulcus (STS) was obtained using fMRI. Activity in this region was found to be greater when subjects heard acoustic sine wave speech stimuli as speech than when they heard the same stimuli as non-speech.reviewe

Altered neocortical tactile but preserved auditory early change detection responses in Friedreich ataxia

Available online 11 May 2019Objective: To study using magnetoencephalography (MEG) the spatio-temporal dynamics of neocortical responses involved in sensory processing and early change detection in Friedreich ataxia (FRDA). Methods: Tactile (TERs) and auditory (AERs) evoked responses, and early neocortical change detection responses indexed by the mismatch negativity (MMN) were recorded using tactile and auditory oddballs in sixteen FRDA patients and matched healthy subjects. Correlations between the maximal amplitude of each response, genotype and clinical parameters were investigated. Results: Evoked responses were detectable in all FRDA patients but one. In patients, TERs were delayed and reduced in amplitude, while AERs were only delayed. Only tactile MMN responses at the contralateral secondary somatosensory cortex were altered in FRDA patients. Maximal amplitudes of TERs, AERs and tactile MMN correlated with genotype, but did not correlate with clinical parameters. Conclusions: In FRDA, the amplitude of tactile MMN responses at SII cortex are reduced and correlate with the genotype, while auditory MMN responses are not altered. Significance: Somatosensory pathways and tactile early change detection are selectively impaired in FRDAThis study was financially supported by (i) the research grant ‘‘Les Voies du Savoir” from the Fonds Erasme (Brussels, Belgium) and (ii) the Fonds de la Recherche Scientifique (FRS-FNRS, Brussels, Belgium; research credit: J.0095.16.F). Gilles Naeije was supported by a research grant from the Fonds Erasme (Brussels, Belgium). Mathieu Bourguignon was supported by the program Attract of Innoviris (grant 2015-BB2B-10), by the Spanish Ministry of Economy and Competitiveness (grant PSI2016-77175-P), and by the Marie Skłodowska-Curie Action of the European Commission (grant 743562). Xavier De Tiège is Postdoctorate Clinical Master Specialist at the Fonds de la Recherche Scientifique (FRS-FNRS, Brussels, Belgium). The MEG project at the CUB Hôpital Erasme is financially supported by the Fonds Erasme (Research grant ‘‘Les Voies du Savoir”, Brussels, Belgium). The authors would like to thank Brice Marty for his help in MEG data acquisition

Somatosensory System Deficits in Schizophrenia Revealed by MEG during a Median-Nerve Oddball Task

Although impairments related to somatosensory perception are common in schizophrenia, they have rarely been examined in functional imaging studies. In the present study, magnetoencephalography (MEG) was used to identify neural networks that support attention to somatosensory stimuli in healthy adults and abnormalities in these networks in patient with schizophrenia. A median-nerve oddball task was used to probe attention to somatosensory stimuli, and an advanced, high-resolution MEG source-imaging method was applied to assess activity throughout the brain. In nineteen healthy subjects, attention-related activation was seen in a sensorimotor network involving primary somatosensory (S1), secondary somatosensory (S2), primary motor (M1), pre-motor (PMA), and paracentral lobule (PCL) areas. A frontal–parietal–temporal “attention network”, containing dorsal- and ventral–lateral prefrontal cortex (DLPFC and VLPFC), orbitofrontal cortex (OFC), anterior cingulate cortex (ACC), superior parietal lobule (SPL), inferior parietal lobule (IPL)/supramarginal gyrus (SMG), and temporal lobe areas, was also activated. Seventeen individuals with schizophrenia showed early attention-related hyperactivations in S1 and M1 but hypo-activation in S1, S2, M1, and PMA at later latency in the sensorimotor network. Within this attention network, hypoactivation was found in SPL, DLPFC, orbitofrontal cortex, and the dorsal aspect of ACC. Hyperactivation was seen in SMG/IPL, frontal pole, and the ventral aspect of ACC in patients. These findings link attention-related somatosensory deficits to dysfunction in both sensorimotor and frontal–parietal–temporal networks in schizophrenia

Oszillatorische Gamma-Band-Aktivität bei der Verarbeitung auditorischer Reize im Kurzzeitgedächtnis im MEG

Recent studies have suggested an important role of cortical gamma oscillatory activity (30-100 Hz) as a correlate of encoding, maintaining and retrieving auditory, visual or tactile information in and from memory. It was shown that these cortical stimulus representations were modulated by attention processes. Gamma-band activity (GBA) occurred as an induced response peaking at approximately 200-300 ms after stimulus presentation. Induced cortical responses appear as non-phase-locked activity and are assumed to reflect active cortical processing rather than passive perception. Induced GBA peaking 200-300 ms after stimulus presentation has been assumed to reflect differences between experimental conditions containing various stimuli. By contrast, the relationship between specific oscillatory signals and the representation of individual stimuli has remained unclear. The present study aimed at the identification of such stimulus-specific gamma-band components. We used magnetoencephalography (MEG) to assess gamma activity during an auditory spatial delayed matching-to-sample task. 28 healthy adults were assigned to one of two groups R and L who were presented with only right- or left-lateralized sounds, respectively. Two sample stimuli S1 with lateralization angles of either 15° or 45° deviation from the midsagittal plane were used in each group. Participants had to memorize the lateralization angle of S1 and compare it to a second lateralized sound S2 presented after an 800-ms delay phase. S2 either had the same or a different lateralization angle as S1. After the presentation of S2, subjects had to indicate whether S1 and S2 matched or not. Statistical probability mapping was applied to the signals at sensor level to identify spectral amplitude differences between 15° and 45° stimuli. We found distinct gamma-band components reflecting each sample stimulus with center frequencies ranging between 59 and 72 Hz in different sensors over parieto-occipital cortex contralateral to the side of stimulation. These oscillations showed maximal spectral amplitudes during the middle 200-300 ms of the delay phase and decreased again towards its end. Additionally, we investigated correlations between the activation strength of the gamma-band components and memory task performance. The magnitude of differentiation between oscillatory components representing 'preferred' and 'nonpreferred' stimuli during the final 100 ms of the delay phase correlated positively with task performance. These findings suggest that the observed gamma-band components reflect the activity of neuronal networks tuned to specific auditory spatial stimulus features. The activation of these networks seems to contribute to the maintenance of task-relevant information in short-term memory.Ergebnisse aus aktuellen Studien legen nahe, dass kortikale oszillatorische Aktivität im Gamma-Bereich (30-100 Hz) eine wichtige Rolle für verschiedene kognitive Prozesse spielt. Dazu zählen das Kodieren, die Aufrechterhaltung und der Abruf auditorischer, visueller oder taktiler Informationen in das bzw. aus dem Gedächtnis. Es konnte gezeigt werden, dass diese kortikale Aktivität durch Aufmerksamkeitsprozesse beeinflusst wird. Gamma-Aktivität trat bei vorangegangenen Untersuchungen als induzierte Antwort ca. 200-300 ms nach Stimuluspräsentation auf. Es wird angenommen, dass diese nicht phasengebundenen kortikalen Reizantworten aktive kortikale Verarbeitungs-prozesse widerspiegeln. In früheren Studien wurde induzierte Gamma-Aktivität während der Aufrechterhaltung von Stimulusinformationen über Regionen gefunden, die an der Verarbeitung aufgabenrelevanter Reizmerkmale beteiligt sind. Diese Antworten im Gamma-Bereich spiegelten Unterschiede zwischen verschieden experimentellen Bedingungen wider, jedoch ist wenig über die Repräsentation spezifischer Stimuluseigenschaften durch Gamma-Aktivität bekannt. Mit der vorliegenden Studie haben wir versucht, solche stimulus spezifischen Gamma-Komponenten zu untersuchen. Dafür verwendeten wir Magnetenzephalographie (MEG) und eine auditorische räumliche “delayed matching-to-sample“ Aufgabe. 28 gesunde Erwachsene wurden dabei zwei verschiedenen Gruppen zugeordnet. Gruppe R bekam rechtslateralisierte Stimuli präsentiert, während diese in Gruppe L linkslateralisiert waren. Dabei unterschieden sich die Reize nur in ihrer räumlichen Charakteristik, die Klangmuster blieben unverändert. In beiden Gruppen wurden zwei Beispielstimuli S1 mit Lateralisierungswinkeln von 15° bzw. 45° verwendet. Die Probanden mussten sich den Lateralisierungswinkel von S1 merken und anschließend mit einem zweiten Stimulus S2, der nach einer Verzögerungsphase von 800 ms präsentiert wurde, vergleichen. S2 hatte dabei entweder den gleichen Lateralisierungswinkel wie S1, oder unterschied sich darin von dem ersten Stimulus. Nach der Präsentation von S2 mussten die Probanden signalisieren, ob die Lateralisierungswinkel der beiden Stimuli übereinstimmten oder nicht. Die Signale der einzelnen Sensoren wurden mit einem statistischen Wahrscheinlichkeitsmapping untersucht. Dabei wollten wir Unterschiede in der spektralen Amplitude für Stimuli mit 15° bzw. 45° Lateralisierungswinkel identifizieren. Wir konnten spezifische Gamma-Aktivität für alle Beispielstimuli nachweisen. Die Signale wurden im Bereich von 59-72 Hz gefunden und waren über dem parieto-okzipitalen Kortex jeweils kontralateral zur stimulierten Seite lokalisiert. Die maximalen Spektralamplituden dieser Oszillationen traten während der mittleren 200-300 ms der Verzögerungsphase auf und nahmen zu ihrem Ende hin ab. Zusätzlich haben wir Korrelationen zwischen der Aktivierungsstärke der Gamma-Komponenten und dem Abschneiden bei der Gedächtnisaufgabe untersucht. Dabei zeigte sich, dass der Unterschied der oszillatorischen Antworten auf bevorzugte und nicht-bevorzugte Stimuli während der letzten 100 ms der Verzögerungsphase positiv mit der Leistung in der Gedächtnisaufgabe korrelierte. Diese Ergebnisse sprechen dafür, dass die beobachteten Gamma Komponenten die Aktivität neuronaler Netzwerke, die auf die Verarbeitung räumlicher auditorischer Information spezialisiert sind, widerspiegeln. Die Aktivierung dieser Netzwerke scheint zur Aufrechterhaltung aufgabenbezogener Information im Kurzzeitgedächtnis beizutragen

Magnetoencephalography

This is a practical book on MEG that covers a wide range of topics. The book begins with a series of reviews on the use of MEG for clinical applications, the study of cognitive functions in various diseases, and one chapter focusing specifically on studies of memory with MEG. There are sections with chapters that describe source localization issues, the use of beamformers and dipole source methods, as well as phase-based analyses, and a step-by-step guide to using dipoles for epilepsy spike analyses. The book ends with a section describing new innovations in MEG systems, namely an on-line real-time MEG data acquisition system, novel applications for MEG research, and a proposal for a helium re-circulation system. With such breadth of topics, there will be a chapter that is of interest to every MEG researcher or clinician