Unsupervised detection and removal of muscle artifacts from scalp EEG recordings using canonical correlation analysis,wavelets and random forests

Objective

This paper proposes supervised and unsupervised algorithms for automatic muscle artifact detection and removal from long-term EEG recordings, which combine canonical correlation analysis (CCA) and wavelets with random forests (RF).

Removal of physiological artifacts from simultaneous EEG and fMRI recordings

ObjectiveSimultaneous recording of the electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) allows a combination of eletrophysiological and haemodynamic information to be used to form a more complete picture of cerebral dynamics. However, EEG recorded within the MRI scanner is contaminated by both imaging artifacts and physiological artifacts. The majority of the techniques used to pre-process such EEG focus on removal of the imaging and balistocardiogram artifacts, with some success, but don’t remove all other physiological artifacts.MethodsWe propose a new offline EEG artifact removal method based upon a combination of independent component analysis and fMRI-based head movement estimation to aid the removal of physiological artifacts from EEG recorded during EEG-fMRI recordings. Our method makes novel use of head movement trajectories estimated from the fMRI recording in order to assist with identifying physiological artifacts in the EEG and is designed to be used after removal of the fMRI imaging artifact from the EEG.ResultsWe evaluate our method on EEG recorded during a joint EEG-fMRI session from healthy adult participants. Our method significantly reduces the influence of all types of physiological artifacts on the EEG. We also compare our method with a state-of-the-art physiological artifact removal method and demonstrate superior performance removing physiological artifacts.ConclusionsOur proposed method is able to remove significantly more physiological artifact components from the EEG, recorded during a joint EEG-fMRI session, than other state-of-the-art methods.SignificanceOur proposed method represents a marked improvement over current processing pipelines for removing physiological noise from EEG recorded during a joint EEG-fMRI session.     

Lateralizing and localizing values of ictal onset recorded on the scalp: evidence from simultaneous recordings with intracranial foramen ovale electrodes

PURPOSE: The value of scalp recordings to localize and lateralize seizure onset in temporal lobe epilepsy has been assessed by comparing simultaneous scalp and intracranial foramen ovale (FO) recordings during presurgical assessment. The sensitivity of scalp recordings for detecting mesial temporal ictal onset has been compared with a "gold standard" provided by simultaneous deep intracranial FO recordings from the mesial aspect of the temporal lobe. As FO electrodes are introduced via anatomic holes, they provide a unique opportunity to record simultaneously from scalp and mesial temporal structures without disrupting the conducting properties of the brain coverings by burr holes and wounds, which can otherwise make simultaneous scalp and intracranial recordings unrepresentative of the habitual EEG. METHODS: Simultaneous FO and scalp recordings from 314 seizures have been studied in 110 patients under telemetric presurgical assessment for temporal lobe epilepsy. Seizure onset was identified on scalp records while blind to recordings from FO electrodes and vice versa. RESULTS: Bilateral onset (symmetric or asymmetric) was more commonly found in scalp than in FO recordings. The contrary was true for unilateral seizure onset. In seizures with bilateral asymmetric onset on the scalp, the topography of largest-amplitude scalp changes at onset does not have localizing or lateralizing value. However, 75-76% of seizures showing unilateral scalp onset with largest amplitude at T1/T2 or T3/T4 had mesial temporal onset. This proportion dropped to 42% among all seizures with a unilateral scalp onset at other locations. Of those seizures with unilateral onset on the scalp at T1/T2, 65.2% showed an ipsilateral mesial temporal onset, and 10.9% had scalp onset incorrectly lateralized with respect to the mesial temporal onset seen on FO recordings. In seizures with a unilateral onset on the scalp at electrodes other than T1/T2, the proportions of seizures with correctly and incorrectly lateralized mesial temporal onset were 37.5 and 4.2%, respectively. Thus the ratio between incorrectly and correctly lateralized mesial temporal onsets is largely similar for seizures with unilateral scalp onset at T1/T2 (16.7%) and for seizures with unilateral scalp onset at electrodes other than T1/T2 (11.2%). The onset of scalp changes before the onset of clinical manifestations is not associated with a lower proportion of seizures with bilateral onset on the scalp, or with a higher percentage of mesial temporal seizures or of mesial temporal seizures starting ipsilateral to the side of scalp onset. In contrast, the majority (78.4%) of mesial temporal seizures showed clinical manifestations starting after ictal onset on FO recordings. CONCLUSIONS: A bilateral scalp onset (symmetric or asymmetric) is compatible with a mesial temporal onset, and should not deter further surgical assessment. Although a unilateral scalp onset at T1/T2 or T3/T4 is associated with a higher probability of mesial temporal onset, a unilateral onset at other scalp electrodes does not exclude mesial temporal onset. A unilateral scalp onset at electrodes other than T1/T2 is less likely to be associated with mesial temporal onset, but its lateralizing value is similar to that of unilateral scalp onset at T1/T2. The presence of clinical manifestations preceding scalp onset does not reduce the localizing or lateralizing values of scalp recordings.     

Effects of threshold,low frequency,long lasting stimulation on single motor unit electrical responses from the extensor digitorum brevis muscle in normal and myasthenic subjects

Summary The authors studied the recruitment of motor units of EDB muscle by long lasting threshold intensity stimulation at 1 c/sec of external popliteal nerve at the ankle in healthy subjects and in myasthenic patients. In the healthy volunteers, at steady intensity of threshold stimuli, maximum number of motor units never exceeded 5–6 electrical increments with a final incremental response of constant amplitude during 60 min of stimulation. In myasthenic patients, both an early exhaustion of threshold motor units and a marked facilitation phenomenon occurred with massive recruitment of incremental responses, while in a small number of cases no changes were observed. These data are discussed in the light of various morphofunctional hypotheses regarding the localization of the myasthenic impairment.

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Zusammenfassung Es wurde die Rekrutierung motorischer Einheiten im Extensor digitorum brevis bei langdauernder repetitiver Reizung des N. peronaeus profundus am Sprunggelenk mit Schwellenstromstärken und einer Frequenz von 1 Hz in gesunden Versuchspersonen und bei Myasthenikern untersucht. In den gesunden Versuchspersonen wurden bei gleichbleibender Intensität der Schwellenreize während 60 min nie mehr als 5–6 Potentialzunahmen, entsprechend der gleichen Zahl neu rekrutierter motorischer Einheiten, beobachtet. Abfallende Antworten traten nie auf. Bei Myasthenikern war sowohl eine frühzeitige Erschöpfung der rekrutierten motorischen Einheiten nachweisbar als auch eine zunehmende Fazilitation mit ausgesprochener Rekrutierung von Potentialzunahmen. Bei einer kleineren Zahl von Patienten war keine Veränderung festzustellen. Diese Ergebnisse werden im Lichte verschiedener morphofunktioneller Hypothesen über die Lokalisation der myasthenischen Störung diskutiert.

     

Effects of depth electrode montage and single-pulse electrical stimulation sites on neuronal responses and effective connectivity

ObjectiveTo determine the optimal depth electrode montages for the assessment of effective connectivity based on single-pulse electrical stimulation (SPES). To determine the effect of SPES locations on the extent of resulting neuronal propagations.MethodsWe studied 14 epilepsy patients who underwent invasive monitoring with depth electrodes and measurement of cortico-cortical evoked potentials (CCEPs) and cortico-cortical spectral responses (CCSRs). We determined the effects of electrode montage and stimulus sites on the CCEP/CCSR amplitudes.ResultsBipolar and Laplacian montages effectively reduced the degree of SPES-related signal deflections at extra-cortical levels, including outside the brain, while maintaining those at the cortical level. SPES of structures more proximal to the deep white matter, compared to the cortical surface, elicited greater CCEPs and CCSRs.ConclusionsOn depth electrode recording, bipolar and Laplacian montages are suitable for measurement of near-field CCEPs and CCSRs. SPES of the white matter axons may induce neuronal propagations to extensive regions of the cerebral cortex.SignificanceThis study helps to establish the practical guidelines on the diagnostic use of CCEPs/CCSRs.