Neural plasticity associated with recently versus often heard objects.

In natural settings the same sound source is often heard repeatedly, with variations in spectro-temporal and spatial characteristics. We investigated how such repetitions influence sound representations and in particular how auditory cortices keep track of recently vs. often heard objects. A set of 40 environmental sounds was presented twice, i.e. as prime and as repeat, while subjects categorized the corresponding sound sources as living vs. non-living. Electrical neuroimaging analyses were applied to auditory evoked potentials (AEPs) comparing primes vs. repeats (effect of presentation) and the four experimental sections. Dynamic analysis of distributed source estimations revealed i) a significant main effect of presentation within the left temporal convexity at 164-215ms post-stimulus onset; and ii) a significant main effect of section in the right temporo-parietal junction at 166-213ms. A 3-way repeated measures ANOVA (hemisphere×presentation×section) applied to neural activity of the above clusters during the common time window confirmed the specificity of the left hemisphere for the effect of presentation, but not that of the right hemisphere for the effect of section. In conclusion, spatio-temporal dynamics of neural activity encode the temporal history of exposure to sound objects. Rapidly occurring plastic changes within the semantic representations of the left hemisphere keep track of objects heard a few seconds before, independent of the more general sound exposure history. Progressively occurring and more long-lasting plastic changes occurring predominantly within right hemispheric networks, which are known to code for perceptual, semantic and spatial aspects of sound objects, keep track of multiple exposures

EEG source localization analysis in epileptic children during a visual working-memory task

We localize the sources of brain activity of children with epilepsy based on EEG recordings acquired during a visual discrimination working memory task. For the numerical solution of the inverse problem, with the aid of age-specific MRI scans processed from a publicly available database, we use and compare three regularization numerical methods, namely the standarized Low Resolution Electromagnetic Tomography (sLORETA), the weighted Minimum Norm Estimation (wMNE) and the dynamic Statistical Parametric Mapping (dSPM). We show that all three methods provide the same spatio-temporal patterns of differences between epileptic and control children. In particular, our analysis reveals statistically significant differences between the two groups in regions of the Parietal Cortex indicating that these may serve as "biomarkers" for diagnostic purposes and ultimately localized treatment

Electroencephalographic source imaging: a prospective study of 152 operated epileptic patients

Electroencephalography is mandatory to determine the epilepsy syndrome. However, for the precise localization of the irritative zone in patients with focal epilepsy, costly and sometimes cumbersome imaging techniques are used. Recent small studies using electric source imaging suggest that electroencephalography itself could be used to localize the focus. However, a large prospective validation study is missing. This study presents a cohort of 152 operated patients where electric source imaging was applied as part of the pre-surgical work-up allowing a comparison with the results from other methods. Patients (n = 152) with >1 year postoperative follow-up were studied prospectively. The sensitivity and specificity of each imaging method was defined by comparing the localization of the source maximum with the resected zone and surgical outcome. Electric source imaging had a sensitivity of 84% and a specificity of 88% if the electroencephalogram was recorded with a large number of electrodes (128-256 channels) and the individual magnetic resonance image was used as head model. These values compared favourably with those of structural magnetic resonance imaging (76% sensitivity, 53% specificity), positron emission tomography (69% sensitivity, 44% specificity) and ictal/interictal single-photon emission-computed tomography (58% sensitivity, 47% specificity). The sensitivity and specificity of electric source imaging decreased to 57% and 59%, respectively, with low number of electrodes (<32 channels) and a template head model. This study demonstrated the validity and clinical utility of electric source imaging in a large prospective study. Given the low cost and high flexibility of electroencephalographic systems even with high channel counts, we conclude that electric source imaging is a highly valuable tool in pre-surgical epilepsy evaluatio

Electroencephalographic source imaging: a prospective study of 152 operated epileptic patients

Electroencephalography is mandatory to determine the epilepsy syndrome. However, for the precise localization of the irritative zone in patients with focal epilepsy, costly and sometimes cumbersome imaging techniques are used. Recent small studies using electric source imaging suggest that electroencephalography itself could be used to localize the focus. However, a large prospective validation study is missing. This study presents a cohort of 152 operated patients where electric source imaging was applied as part of the pre-surgical work-up allowing a comparison with the results from other methods. Patients (n = 152) with >1 year postoperative follow-up were studied prospectively. The sensitivity and specificity of each imaging method was defined by comparing the localization of the source maximum with the resected zone and surgical outcome. Electric source imaging had a sensitivity of 84% and a specificity of 88% if the electroencephalogram was recorded with a large number of electrodes (128–256 channels) and the individual magnetic resonance image was used as head model. These values compared favourably with those of structural magnetic resonance imaging (76% sensitivity, 53% specificity), positron emission tomography (69% sensitivity, 44% specificity) and ictal/interictal single-photon emission-computed tomography (58% sensitivity, 47% specificity). The sensitivity and specificity of electric source imaging decreased to 57% and 59%, respectively, with low number of electrodes (<32 channels) and a template head model. This study demonstrated the validity and clinical utility of electric source imaging in a large prospective study. Given the low cost and high flexibility of electroencephalographic systems even with high channel counts, we conclude that electric source imaging is a highly valuable tool in pre-surgical epilepsy evaluation

Multimodale Bildgebung in der prächirurgischenEpilepsiediagnostik bei Kindern und Jugendlichen

Kinder mit einer Epilepsie, die nicht auf Medikamente ansprechen, können durch einen operativen Eingriff geheilt werden. In der prächirurgischen Diagnostik dieser Kinder ist es notwendig die epileptogene Zone eindeutig zu bestimmen: dazu bedarf es Hypothesen. Verschiedene Verfahren (Elektroenzephalographie, Magnetresonanztomographie, Positron-Emissions-Tomographie, Single-Photon-Emissionscom-putertomographie) werden aktuell angewandt. Doch keine der genannten Methoden kann die epileptogene Zone mit der erforderlichen Sicherheit eingrenzen, jede hat Limitationen, so dass es auf die Zusammenschau der Verfahren ankommt. Deshalb wurde in dieser Studie erstmalig bei Kindern mit symptomatischen und kryptogenen fokalen Epilepsien die Kombination aus der simultanen Ableitung von Elektroenzephalographie und der Aufzeichnung von funktioneller Magnetresonanztomographie in Kombination mit einer Quellenanlyse untersucht. Die Kombination von Elektroenzephalographie und funktioneller Magnetresonanztomographie ist eine nicht invasive Methode, die hämodynamische Veränderungen im gesamten Gehirn während interiktaler epileptischer Aktivität detektieren kann. Dabei werden bei 540 Magnetresonanz-Aufnahmen mit schnellen Sequenzen die Unterschiede dargestellt, die einerseits zwischen den Aufnahmen bestehen, bei denen eine interiktale epileptische Aktivität im Elektroenzephalogramm zu sehen war und andererseits zwischen den Aufnahmen, bei denen dies nicht der Fall war. In früheren Studien bei Kindern mit verschiedenen Epilepsieformen zeigte sich je-doch, dass die Ergebnisse selten lokalisiert, sondern meist ausgedehnt zur Darstel-lung kamen. Daher untersuchten wir, ob eine Kombination mit einer Quellenanalyse, die auf verteilten Quellen basiert, diese ausgedehnten Aktivierungsareale zeitlich differenzieren kann. Wir wählten von 26 Patienten, die an einem epilepsiechirurgischen Programm teil-nahmen, sechs Patienten aus, die einen klaren erwarteten epileptogenen Fokus durch Übereinstimmung von Positron-Emissions-Tomographie, iktaler Single-Photon-Emissionscomputertomographie und Video-Elektroenzephalographie zeigten. Bei allen Patienten fanden wir eine signifikante Signaländerung in der Elektroenzephalographie und funktioneller Magnetresonanztomographie sowie eine Übereinstimmung mit der erwarteten epileptogenen Zone bei fünf Patienten. Bei fünf Patienten sahen wir zusätzlich ausgedehnte Aktivierungsareale. Die Quel-lenanalyse zeigte, dass der Beginn der interiktalen epileptischen Aktivität bei allen Patienten in der erwarteten epileptogenen Zone lag und bei fünf Patienten eine Verlagerung in nahe Gehirnregionen erfolgte. Diese Ausbreitungen der Quellen korrespondierten mit Arealen der Signaländerungen im funktionellen MRT. Die Kombination von Elektroenzephalographie und funktioneller Magnetresonanztomographie ist eine Methode, die signifikante Aktivierungen im Bereich der epileptogenen Zone zeigen kann, jedoch sind diese Aktivierungen meist darüber hinaus ausgebreitet, so dass es zusätzlicher Methoden bedarf, diese ausgedehnten Bereiche zu erklären. Die Quellenanalyse, die auf verteilte Quellen basiert, ist in der Lage, die Ergebnisse der funktionellen Magnetresonanztomographie durch die hohe zeitliche Auflösung zu interpretieren und für die prächirurgische Diagnostik zu verbessern

Untersuchung neuronaler Netzwerke bei West Syndrom mittels Quellenanalyse und partial directed coherence

West syndrome is a severe epileptic encephalopathy of infancy with a poor developmental outcome. This syndrome is associated with the pathognomonic EEG feature of hypsarrhythmia. The aim of the study was to describe neuronal networks underlying hypsarrhythmia using the source analysis method (dynamic imaging of coherent sources or DICS) which represents an inverse solution algorithm in the frequency domain. In order to investigate the interaction within the detected network, a renormalized partial directed coherence (RPDC) method was also applied as a measure of the directionality of information flow between the source signals

Neuronal networks of burst suppression EEG as revealed by source analysis and renormalized partial directed coherence

Burst-suppression (BS) is an electroencephalography (EEG) pattern consist-ing of alternative periods of slow waves of high amplitude (the burst) and periods of so called flat EEG (the suppression). It is generally associated with the reduced level of consciousness. The aim of this study was to reveal the neuronal network underlying both burst and suppression phases using a source analysis method: dynamic imaging of coherent sources (DICS) and to describe the effective connectivity between the identified sources using renormalized partial directed coherence (RPDC). DICS was applied separately to the EEG segments of 13 neonates with burst and suppression EEG pattern. Power spectrum analyses were performed to identify the predominant frequencies. The brain area with the strongest power in the analyzed frequency (1-4 Hz) range was defined as the reference region. DICS was used to compute the coher-ence between this reference region and the entire brain. RPDC was used to describe the in-formational flow between the described sources. Delta activity during burst phases was associated with sources in the thalamus and brainstem as well as bilateral sources in the cortical regions mainly frontal and parietal, whereas suppression phases were associated with coherent sources only in the cor-tical regions. Results of the RPDC analyses showed an ascending informational flow from the brainstem towards the thalamus and from the thalamus to cortical regions, which was absent during suppression phases. Especially those brain regions were affected, that are im-portant for cognitive processing. The results of this study strengthen the assumption that there is a specific periodicity of neural activity and that thalamocortical deafferentiation is an essential feature of BS. Thus a burst can be understood as short, repetitive recovery of cortical neural dynamics. The described deafferentation may play a role in the poor neuro-logical outcome in these encephalopathies

Combination of EEG-fMRI and EEG source analysis improves interpretation of spike-associated activation networks in paediatric pharmacoresistant focal epilepsies

Simultaneous recording of EEG and functional MRI (EEG-fMRI) is a promising tool that may be applied in patients with epilepsy to investigate haemodynamic changes associated with interictal epileptiform discharges (IED). As the yield of the EEG-fMRI technique in children with epilepsy is still unclear, the aim of this study was to evaluate whether the combination of EEG-fMRI and EEG source analysis could improve localization of epileptogenic foci in children. Six children with an unambiguous focus localization were selected based on the criterion of the consistency of ictal EEG, PET and ictal SPECT. IEDs were taken as time series for fMRI analysis and as averaged sweeps for the EEG source analysis based on the distributed linear local autoregressive average (LAURA) solution. In four patients, the brain area with haemodymanic changes corresponded to the epileptogenic zone. However, additional distant regions with haemodynamic response were observed. Source analysis located the source of the initial epileptic activity in all cases in the presumed epileptogenic zone and revealed propagation in five cases. In three cases there was a good correspondence between haemodynamic changes and source localization at both the beginning and the propagation of IED. In the remaining three cases, at least one area of haemodynamic changes corresponded to either the beginning or the propagation. In most children analysed, EEG-fMRI revealed extended haemodynamic response, which were difficult to interpret without an appropriate reference, i.e. a priori hypothesis about epileptogenic zone. EEG source analysis may help to differentiate brain areas with haemodynamic response

Das Default Mode Network als treibende Kraft hinter Spike-wave Entladungen bei idiopathischen generalisierten Epilepsien

Der Zweck unserer Studie war die Identifikation der Netzwerke, welche an der Generierung und zeitlichen Entwicklung von GSW beteiligt sind, um Rückschlüsse auf den Ursprung und die Ausbreitung der epileptischen Aktivität ziehen zu können. Hierfür wurde mittels EEG-fMRT Lokalisation und Propagation von Spike-wave Komplexen bei Patienten mit IGE (sowohl CAE/JAE als auch JME) auf intra- und interindividueller Ebene untersucht, um die jeweils beteiligten Strukturen herauszufinden. Auf diese Weise konnten wir die epileptische Aktivität mit der BOLD-Antwort des fMRT korrelieren und die aktivierten Regionen identifizieren. Im Ergebnis zeigte sich, dass trotz interindividueller Unterschiede, was die zeitliche Abfolge der Aktivitätsänderungen betrifft, die betroffenen Hirnareale bei allen Patienten durchweg sehr ähnlich waren. Wir beobachteten Signalveränderungen im Thalamus, DMN, Dorsal Attention Network, Salience Network, Basalganglien, dorsolateralen prefrontalen Kortex und im Motorkortex mit supplementärem Motorkortex. So detektierten wir Deaktivierungen im DMN und DAN und Aktivierungen in SN und Thalamus, welche jeweils dem Beginn der GSW im EEG einige Sekunden voraus gingen. Die DCM Analyse erbrachte letztendlich, dass die treibende Kraft der GSW in IGE im DMN begründet liegt. Das beobachtete Wechselspiel zwischen DMN, DAN, SN und Thalamus zeigt eine Runterregulierung des Bewusstseins zugunsten einer verstärkten interozeptiven autonomen Verarbeitung. Das DMN scheint eine zentrale Rolle als Antriebskraft hinter diesen Veränderungen zu spielen. Insgesamt gab es jedoch deutliche Unterschiede in den Aktivitätsmustern der einzelnen Patienten, was eine signifikante Heterogenität in IGE bedeutet trotz des scheinbar homogenen klinischen Bildes