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.
Fernandes
José Maria
JM
Department of Electronics and Telecommunications and IEETA, University of Aveiro, Portugal. jfernan@ieeta.pt
da Silva
António Martins
AM
Huiskamp
Geertjan
G
Velis
Demetrios N
DN
Manshanden
Ilonka
I
de Munck
Jan C
JC
da Silva
Fernando Lopes
FL
Cunha
João Paulo Silva
JP
D000328:Adult; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000503:physiopathology* / Q000528:radiation effects; D004567:Electrodes, Implanted; D004569:Electroencephalography; D004827:Epilepsy / Q000503:physiopathology*; D005260:Female; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D008959:Models, Neurological; D012815:Signal Processing, Computer-Assisted