Source localization methods

Stefano Seri, Antonella Cerquiglini

Research output: Chapter in Book/Report/Conference proceedingChapter (peer-reviewed)

Abstract

One of the most pressing demands on electrophysiology applied to the diagnosis of epilepsy is the non-invasive localization of the neuronal generators responsible for brain electrical and magnetic fields (the so-called inverse problem). These neuronal generators produce primary currents in the brain, which together with passive currents give rise to the EEG signal. Unfortunately, the signal we measure on the scalp surface doesn't directly indicate the location of the active neuronal assemblies. This is the expression of the ambiguity of the underlying static electromagnetic inverse problem, partly due to the relatively limited number of independent measures available. A given electric potential distribution recorded at the scalp can be explained by the activity of infinite different configurations of intracranial sources. In contrast, the forward problem, which consists of computing the potential field at the scalp from known source locations and strengths with known geometry and conductivity properties of the brain and its layers (CSF/meninges, skin and skull), i.e. the head model, has a unique solution. The head models vary from the computationally simpler spherical models (three or four concentric spheres) to the realistic models based on the segmentation of anatomical images obtained using magnetic resonance imaging (MRI). Realistic models – computationally intensive and difficult to implement – can separate different tissues of the head and account for the convoluted geometry of the brain and the significant inter-individual variability. In real-life applications, if the assumptions of the statistical, anatomical or functional properties of the signal and the volume in which it is generated are meaningful, a true three-dimensional tomographic representation of sources of brain electrical activity is possible in spite of the ‘ill-posed’ nature of the inverse problem (Michel et al., 2004). The techniques used to achieve this are now referred to as electrical source imaging (ESI) or magnetic source imaging (MSI). The first issue to influence reconstruction accuracy is spatial sampling, i.e. the number of EEG electrodes. It has been shown that this relationship is not linear, reaching a plateau at about 128 electrodes, provided spatial distribution is uniform. The second factor is related to the different properties of the source localization strategies used with respect to the hypothesized source configuration.

Original languageEnglish
Title of host publicationIntroduction to epilepsy
EditorsGonzalo Alarcón, Antonio Valentín
Place of PublicationCambridge (UK)
PublisherCambridge University Press
Pages269-272
Number of pages4
ISBN (Electronic)978-1-13933468-6, 978-1-13910399-2
ISBN (Print)978-0-521-69158-1
DOIs
Publication statusPublished - Apr 2012

Fingerprint

Scalp
Brain
Head
Electroencephalography
Electrodes
Meninges
Electrophysiology
Electromagnetic Phenomena
Magnetic Fields
Skull
Epilepsy
Magnetic Resonance Imaging
Skin

Cite this

Seri, S., & Cerquiglini, A. (2012). Source localization methods. In G. Alarcón, & A. Valentín (Eds.), Introduction to epilepsy (pp. 269-272). Cambridge (UK): Cambridge University Press. https://doi.org/10.1017/CBO9781139103992.046
Seri, Stefano ; Cerquiglini, Antonella. / Source localization methods. Introduction to epilepsy. editor / Gonzalo Alarcón ; Antonio Valentín. Cambridge (UK) : Cambridge University Press, 2012. pp. 269-272
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Seri, S & Cerquiglini, A 2012, Source localization methods. in G Alarcón & A Valentín (eds), Introduction to epilepsy. Cambridge University Press, Cambridge (UK), pp. 269-272. https://doi.org/10.1017/CBO9781139103992.046

Source localization methods. / Seri, Stefano; Cerquiglini, Antonella.

Introduction to epilepsy. ed. / Gonzalo Alarcón; Antonio Valentín. Cambridge (UK) : Cambridge University Press, 2012. p. 269-272.

Research output: Chapter in Book/Report/Conference proceedingChapter (peer-reviewed)

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Seri S, Cerquiglini A. Source localization methods. In Alarcón G, Valentín A, editors, Introduction to epilepsy. Cambridge (UK): Cambridge University Press. 2012. p. 269-272 https://doi.org/10.1017/CBO9781139103992.046