Looking for neuronal currents using MRI: an EEG-fMRI investigation of fast MR signal changes time-locked to frequent focal epileptic discharges.
BACKGROUND
Reproducible direct measurement of neuronal electrical activity using MRI signal changes due to local magnetic field perturbations would represent a step change in neuroimaging methods. While some previous studies using experiments based on evoked and spontaneous activity provided encouraging results no clear demonstration of neuronal current-related MR changes in the human brain has emerged to date. The availability of simultaneously acquired EEG-fMRI in patients with frequent interictal epileptic discharges (IED), which have significantly greater amplitude than evoked potentials, offers the opportunity to further investigate the phenomenon.


METHODS
We re-analysed simultaneously acquired EEG-fMRI data in 6 epilepsy patients with very frequent focal IED and a well-localised generator. A model of MRI signal changes due to fast activity and BOLD signal changes was used to identify fast MR signal changes, potentially directly reflecting neuronal activity. Simultaneously-acquired EEG allowed the comparison of electrical source localisation (ESI), clinical epilepsy localisation and BOLD signal changes with the fast MR signal changes.


RESULTS
Clusters of IED-related fast MR signal change were observed in all cases. Spatial correspondence between the IED-related fast MR, BOLD, ESI clusters and irritative zone (IZ) was observed in one slice of a single dataset. The other IED-related fast MR clusters were remote from electro-clinically determined generators of interictal activity. The sign and magnitude of the fast MR signal changes varied across regions and subjects.


CONCLUSIONS
The observed fast MR changes cannot be confidently attributed to the direct effect of neuronal currents due to lack of spatial concordance with generators of interictal activity, IED-related BOLD clusters and ESI estimates.
Rodionov
Roman
R
Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, University College London, London, UK. r.rodionov@ion.ucl.ac.uk
Siniatchkin
Michael
M
Michel
Christoph M
CM
Liston
Adam D
AD
Thornton
Rachel
R
Guye
Maxime
M
Carmichael
David W
DW
Lemieux
Louis
L
D000293:Adolescent; D000328:Adult; D001921:Brain / Q000098:blood supply / Q000503:physiopathology*; D002648:Child; D004569:Electroencephalography / Q000379:methods*; D004827:Epilepsy / Q000503:physiopathology*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008959:Models, Neurological; D010100:Oxygen / Q000097:blood; D012815:Signal Processing, Computer-Assisted; D009435:Synaptic Transmission / Q000502:physiology*; D013997:Time Factors
D010100:Oxygen