What Does an Epileptiform Spike Look Like in MEG? Comparison Between Coincident EEG and MEG Spikes

Recent investigations suggest that there are differences between the characteristics of EEG and MEG epileptiform spikes. The authors performed an objective characterization of the morphology of epileptiform spikes recorded simultaneously in both EEG and MEG to determine whether they present the same morphologic characteristics. Based on a stepwise approach, the authors performed a computer analysis of EEG and MEG of a set of coincident epileptiform transients selected by a senior clinical neurophysiologist in recordings of three patients with drug-resistant epilepsy. A computer-based algorithm was applied to extract parameters that could be used to describe quantitatively the morphology of the transients, followed by a statistical comparison over the extracted metrics of the EEG and MEG waveforms. EEG and MEG coincident events were statistically different with respect to several morphologic characteristics, such as duration, sharpness, and shape. The differences found appear to be a consequence of MEG signals not being influenced by volume propagation through the tissues with different conductivities that surround the brain, compared with EEG, and of the different orientation of the underlying dipolar sources. The results indicate that visual inspection of MEG spikes and automatic spike-detector algorithms should use criteria adapted to the specific characteristics of the MEG, and not simply those used on conventional EEG.

[1]  J. Ebersole.  Defining epileptogenic foci: past, present, future. , 1997, Journal of clinical neurophysiology : official publication of the American Electroencephalographic Society.

[2]  J. Gotman,et al.  Automatic recognition and quantification of interictal epileptic activity in the human scalp EEG. , 1976, Electroencephalography and Clinical Neurophysiology.

[3]  P H Crandall,et al.  The magnetic and electric fields agree with intracranial localizations of somatosensory cortex , 1988, Neurology.

[4]  F H Lopes da Silva,et al.  A topographical display of epileptiform transients based on a statistical approach. , 1980, Electroencephalography and clinical neurophysiology.

[5]  J Gotman,et al.  Automatic detection of seizures and spikes. , 1999, Journal of clinical neurophysiology : official publication of the American Electroencephalographic Society.

[6]  J D Frost,et al.  Automatic Recognition and Characterization of Epileptiform Discharges in the Human EEG , 1985, Journal of clinical neurophysiology : official publication of the American Electroencephalographic Society.

[7]  P H Crandall,et al.  The magnetic field of epileptic spikes agrees with intracranial localizations in complex partial epilepsy , 1988, Neurology.

[8]  J. D. Munck,et al.  Magnetic source imaging contributes to the presurgical identification of sensorimotor cortex in patients with frontal lobe epilepsy , 2003, Clinical Neurophysiology.

[9]  S. Shapiro,et al.  An Analysis of Variance Test for Normality (Complete Samples) , 1965 .

[10]  B. P. Murphy,et al.  Handbook of Methods of Applied Statistics , 1968 .

[11]  P Guedes de Oliveira,et al.  Spike detection based on a pattern recognition approach using a microcomputer. , 1983, Electroencephalography and clinical neurophysiology.

[12]  C. Binnie,et al.  A glossary of terms most commonly used by clinical electroencephalographers. , 1974, Electroencephalography and clinical neurophysiology.

[13]  P H Crandall,et al.  Localization of partial epilepsy using magnetic and electric measurements. , 1991, Epilepsia.

[14]  F Mauguière,et al.  Apparent asynchrony between interictal electric and magnetic spikes , 1997, Neuroreport.

[15]  J R Carrie.  A hybrid computer system for detecting and quantifying spike and wave EEG patterns. , 1972, Electroencephalography and clinical neurophysiology.

[16]  F. H. Lopes da Silva,et al.  Biophysical aspects of EEG and magnetoencephalogram generation , 1998 .

[17]  D Van 't Ent,et al.  Spike cluster analysis in neocortical localization related epilepsy yields clinically significant equivalent source localization results in magnetoencephalogram (MEG) , 2003, Clinical Neurophysiology.

[18]  Maeike Zijlmans,et al.  Modality-specific Spike Identification in Simultaneous Magnetoencephalography/Electroencephalography: A Methodological Approach , 2002, Journal of clinical neurophysiology : official publication of the American Electroencephalographic Society.