Neuromagnetic Evidence of Spatially Distributed Sources Underlying Epileptiform Spikes in the Human Brain

Barth, Daniel S.; Sutherling, William W.; Engle, Jerome; Beatty, Jackson

doi:10.1126/science.6422552

Cited by 185 publications

(39 citation statements)

References 11 publications

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“…There are two basic kinds of measurements made on the human brain. In the first, one detects spontaneous activity: a classic example is the generation of magnetic pulses by subjects suffering from focal epilepsy 70 • The second kind involves evoked response: for example, Romani et al 71 detected the magnetic signal from the auditory cortex generated by tones of different frequencies. Romani has given a extensive review of this work elsewhere in these proceedings.…”

Section: 3)mentioning

confidence: 99%

SQUID Concepts and Systems

Clarke

1989

Superconducting Electronics

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Section: 3)mentioning

confidence: 99%

SQUID Concepts and Systems

Clarke

1989

Superconducting Electronics

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“…Despite numerous electrical (10) and magnetic (11)(12)(13)(14)(15)(16)(17) experiments involving this modality, variations in the cortical anatomy across subjects have not yet been shown to affect these measures. It should be noted that localization of equivalent current dipole sources for interictal epileptiform activity based on neuromagnetic measures has agreed with the positions of large lesions seen in computerized tomography (CT) scans (18)(19)(20), but even in these cases there was no a priori knowledge that the activity should be associated with the particular area of the lesion.…”

mentioning

confidence: 94%

Magnetic localization of neuronal activity in the human brain.

Yamamoto

Williamson

Kaufman

et al. 1988

Proc. Natl. Acad. Sci. U.S.A.

169

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The performance of a cryogenic system that monitors the extracranial magnetic field simultaneously at 14 positions over the scalp has been evaluated to determine the accuracy with which neuronal activity can be located within the human brain. Initially, measurements were implemented on two model systems, a lucite sphere filled with saline and a model skull. With a magnetic field strength similar to that of a human brain, the measurement and analysis procedures demonstrated a position accuracy better than 3 mm, for a current dipole 3 cm beneath the surface. Subsequently, measurements of the magnetic field pattern appearing 100 ms after the onset of an auditory tone-burst stimulus were obtained in three human subjects. The location of the current dipole representing intracellular ionic current in active neurons of the brain was determined, with 3-mm accuracy, to be within the cortex foring the floor of the Sylvian fissure of the individual subjects, corresponding closely to the Heschl gyrus as determined from magnetic resonance images. With the sensors placed at appropriate positions, the locations of neuronal sources for different tone frequencies could be obtained without moving the recording instrument. Adaptation of activity in human auditory cortex was shown to reveal long-term features with a paradigm that compared response amplitudes for three tones randomly presented.Locating neuronal activity within the human brain by measuring the concomitant extracranial magnetic field pattern has been a laborious procedure with single-sensor instruments. Typically, 40 or more positions must be sequentially measured over the scalp, which may take as long as 6 hr to complete. The development of multisensor systems (1-4) made it possible to improve the efficiency of this process, an advance that is of considerable importance for both clinical and research applications. We have installed, at the New York University Medical Center, a commercially available 14-sensor system (Biomagnetic Technologies, San Diego, CA) representing state-of-the-art performance and have evaluated techniques to locate accurately the three-dimensional position of neuronal activity within the human brain (the 14-sensor system consists of two model 607 neuromagnetometers).The effectiveness of these systems has been evaluated through measurements on two types of carefully designed physical models or "phantoms" (a lucite sphere and a plastic skull), both containing a conducting fluid in which an electrical current dipole was placed at a known position. Measurements were made with field strengths at physiological levels (500 ff); this is an important distinction between this and prior studies (5, 6). scans (18-20), but even in these cases there was no a priori knowledge that the activity should be associated with the particular area of the lesion.Obtaining the position of a localized source from a field map across the scalp is conceptually simple if neuronal activity is sufficiently well confined to enable it to be modeled as an equivalent curr...

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“…They reported multiple propagating sources of spikes (19,20) and (based on the three-shell spherical head model) used their different orientations as the main argument for differentiation of mesial temporal versus neocortical temporal or frontal origin (1,lS). However, a major drawback of these approaches was the low spatial resolution because dipoles are much more sensitive to orientation than to transverse dislocation.…”

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Dipole‐Source Analysis in a Realistic Head Model in Patients with Focal Epilepsy

et al. 2000

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Summary:Purpose: By the use of three different head models in EEG dipole analysis, we tried to model the origin of interictal and ictal epileptic activity as precisely as possible. Further, as a control, a second evaluation was made by an independent group to control for interindividual reliability of the dipole source analysis. With the realistic head model (CURRY) considering cortex, skull, and skin segmentation, the spike source was located.Methods: In five patients with mesial temporal epileptogenesis, confirmed by successful epilepsy surgery, the spike source was close to the hippocampus, with a mean distance of the dipole source from the hippocampus of 13.6 mm (range, 9-17.2 mm). In one case the ictal EEG also could be analyzed and resulted in a dipole-source localization comparable to the interictal source. Results:In both head models using either pure cortex segmentation only or a concentric three-shell model, the dipole source was systematically dislocated in a more superior position. Data analysis by a second group with independently chosen EEG samples and identical individual head model resulted in deviations of 4 . 3 mm. Data analysis using independently selected spikes and independently segmented head models resulted in deviations 5 16.7 mm.Conclusions: In four cases of extratemporal epileptogenesis, the origin of interictal epileptiform discharges was localized to the suspected primary epileptogenic zone.

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Neuromagnetic Evidence of Spatially Distributed Sources Underlying Epileptiform Spikes in the Human Brain

Cited by 185 publications

References 11 publications

SQUID Concepts and Systems

SQUID Concepts and Systems

Magnetic localization of neuronal activity in the human brain.

Dipole‐Source Analysis in a Realistic Head Model in Patients with Focal Epilepsy

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