Abstract
Interictal or ictal events in partial epilepsies may project on scalp EEG contralaterally to the side of the epileptogenic lesion. Such paradoxical lateralization can be observed in case of para-sagittal generators, and is likely due to the spatial orientation of the generator, presenting an oblique projection towards the midline. We present here a case of medial occipital epilepsy investigated using EEG, MEG and stereoelectroencephalography (SEEG). MRI displayed a focal cortical dysplasia in the superior margin of the right calcarine fissure. SEEG demonstrated bilateral medial occipital interictal spikes, with an inversion of polarity at the level of the lesion and a contralateral propagation occurring in 10 ms. Interictal iterative EEG cartographies showed a large posterior field, with a maximum contralateral to the initial generator (EEG paradoxical lateralization). With the same number of channels, interictal iterative MEG cartographies were more precise and more complex than EEG ones, indicating an onset accurately lateralized. A few milliseconds later, MEG cartographies were quadripolar, thus indicating two homotopic active generators. These MEG and EEG cartographies have been reproduced using BESA dipole simulator. Relative merits of MEG and EEG are still debated. With 151 channels, MEG source localizations indicated the right medial occipital area, as demonstrated by SEEG. An investigation with a corresponding number of EEG channels was not performed. After a down sampling to 64 sensors, this precision was lost. MEG and EEG source localization results, both with 64 channels, were quite comparable, indicating both medial occipital areas. However, a careful analysis of MEG/EEG iterative cartographies, performed with the same number of channels in both modalities, demonstrated that, in this configuration, MEG sensitivity was superior to the EEG one, allowing separating two medial occipital sources, characterized in SEEG by a time delay of 10 ms.
This is a preview of subscription content, log in via an institution to check access.
References
Barett G, Blumhardt L, Halliday AM, Halliday E, Kriss A (1976) A paradox in the lateralisation of the visual evoked response. Nature 261:253–255
Barkley GL (2004) Controversies in neurophysiology. MEG is superior to EEG in localization of interictal epileptiform activity: pro. Clin Neurophysiol 115:1001–1009
Baumgartner C (2004) Controversies in clinical neurophysiology. MEG is superior to EEG in the localization of interictal epileptiform activity. Controv Clin Neurophysiol 115:1010–1020
Catarino CB, Vollmar C, Noachtar S (2012) Paradoxical lateralization of non-invasive electroencephalographic ictal patterns in extra-temporal epilepsies. Epilepsy Res 99:147–155
Cheyne D, Bostan AC, Gaetz W, Pang EW (2007) Event-related beamforming: a robust method for presurgical functional mapping using MEG. Clin Neurophysiol 118:1691–1704
Cruse R, Klem G, Lesser RP, Leuders H (1982) Paradoxical lateralization of cortical potentials evoked by stimulation of posterior tibial nerve. Arch Neurol 39:222–225
De Tiège X, Carrette E, Legros B, Vonck K, Op de Beeck M, Bourguignon M, Massager N, David P, Van Roost D, Meurs A, Lapere S, Deblaere K, Goldman S, Boon P, Van Bogaert P (2012) Clinical added value of magnetic source imaging in the presurgical evaluation of refractory focal epilepsy. J Neurol Neurosurg Psychiatry 83:417–423
Gavaret M, Trébuchon A, Bartolomei F, Marquis P, McGonigal A, Wendling F, Regis J, Badier JM, Chauvel P (2009) Source localization of scalp-EEG interictal spikes in posterior cortex epilepsies investigated by HR-EEG and SEEG. Epilepsia 50:276–289
Gloor P (1985) Neuronal generators and the problem of localization in electroencephalography: application of volume conductor theory to electroencephalography. J Clin Neurophysiol 2:327–354
Goldenholz DM, Ahlfors SP, Hämäläinen MS, Sharon D, Ishitobi M, Vaina LM, Stufflebeam SM (2009) Mapping the signal-to-noise-ratios of cortical sources in magnetoencephalography and electroencephalography. Hum Brain Mapp 30:1077–1086
Iwasaki M, Pestana E, Burgess RC, Lüders HO, Shamoto H, Nakasato N (2005) Detection of epileptiform activity by human interpreters: blinded comparison between electroencephalography and magnetoencephalography. Epilepsia 46:59–68
Lantz G, de Grave Peralta R, Spinelli L, Seeck M, Michel CM (2003) Epileptic source localization with high density EEG: how many electrodes are needed? Clin Neurophysiol 114:63–69
Lesser RP, Lüders H, Dinner DS, Hahn J, Morris H, Wyllie E, Resor S (1987) The source of ‘paradoxical lateralization’ of cortical evoked potentials to posterior tibial nerve stimulation. Neurology 37:82–88
Malmivuo J (2012) Comparison of the properties of EEG and MEG in detecting the electric activity of the brain. Brain Topogr 25:1–19
Manshanden I, De Munck JC, Simon NR, Lopes da Silva FH (2002) Source localization of MEG sleep spindles and the relation to sources of alpha band rhythms. Clin Neurophysiol 113:1937–1947
Mosher JC, Lewis PS, Leahy RM (1992) Multiple dipole modeling and localization from spatio-temporal MEG data. IEEE Trans Biomed Eng 39:541–557
Oishi A, Tobimatsu S, Ochi H, Ohyagi Y, Kubota T, Taniwaki T, Yamamoto T, Furuya H, Kira J (2002) Paradoxical lateralization of parasagittal spikes revealed by back averaging of EEG and MEG in a case with epilepsia partialis continua. J Neurol Sci 193:151–155
Ossenblok P, de Munck JC, Colon A, Drolsbach W, Boon P (2007) Magnetoencephalography is more successful for screening and localizing frontal lobe epilepsy than electroencephalography. Epilepsia 48:2139–2149
Tomberg C, Weinberg H, Vrba J, Tcheung T (2005) Paradoxical scalp lateralization of the P100 cognitive somatic potential in humans: a magnetic field study. Neurosci Lett 391:68–70
Tukel K, Jasper H (1952) The electroencephalogram in parasagittal lesions. Electroencephalogr Clin Neurophysiol 4(4):481–494
Van Veen BD, van Drongelen W, Yuchtman M, Suzuki A (1997) Localization of brain electrical activity via linearly constrained minimum variance spatial filtering. IEEE Trans Biomed Eng 44:867–880
Acknowledgments
The authors thank Professor Jean Régis for his neurosurgical contribution, Dr. Aileen McGonigal for the revision of the English version and Denis Schwartz for his assistance.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Gavaret, M., Badier, JM., Bartolomei, F. et al. MEG and EEG Sensitivity in a Case of Medial Occipital Epilepsy. Brain Topogr 27, 192–196 (2014). https://doi.org/10.1007/s10548-013-0317-7
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s10548-013-0317-7