EEG spectral changes underlying BOLD responses contralateral to spikes in patients with focal epilepsy.
OBJECTIVE
Simultaneous electroencephalogram and functional magnetic resonance imaging (EEG-fMRI) in patients with focal epilepsy and unilateral spikes often shows positive blood oxygenation level-dependent (BOLD) responses (activations), not only ipsilateral but also contralateral to the spikes. We aimed to investigate whether minimal EEG changes could underlie these contralateral BOLD responses by using EEG spectral analysis.


METHODS
We studied 19 patients with focal epilepsy and unilateral spikes. According to the pattern of BOLD activation, patients were divided into Group 1 (ipsi- and contralateral to the spikes) or Group 2 (only ipsilateral). EEG from outside the scanner was used to mark spikes similar to those recorded in the scanner. Epochs of 640 ms before and after the peak of the spikes were chosen as baseline and spike epochs. Spectral analysis was performed in referential montage (FCz reference), and differences between baselines and spikes were analyzed by paired t-test.


RESULTS
Significant EEG changes in electrodes contralateral to the spikes were seen in 9 of 10 patients in Group 1 and in only 2 of 10 patients in Group 2 (one patient had two types of spikes that were analyzed separately). Spectral changes were seen in delta and/or theta bands in all patients except one (in Group 1) who had changes in all bands.


CONCLUSIONS
Significant contralateral EEG changes occurred in 90% of contralateral BOLD activations and in only 20% of patients without contralateral BOLD responses. The reason why these changes predominate in lower frequencies rather than in higher frequencies is unclear. These spectral changes in areas corresponding to contralateral activations might reflect poorly synchronized but possibly intense neuronal activity.
Yu
Juming M
JM
Montreal Neurological Institute and Department of Neurology and Neurosurgery, McGill University, Montreal, Canada.
Tyvaert
Louise
L
Levan
Pierre
P
Zelmann
Rina
R
Dubeau
François
F
Gotman
Jean
J
Kobayashi
Eliane
E
D000293:Adolescent; D000328:Adult; D001931:Brain Mapping / Q000379:methods*; D002540:Cerebral Cortex / Q000503:physiopathology*; D002648:Child; D004569:Electroencephalography / Q000379:methods / Q000706:statistics & numerical data*; D004828:Epilepsies, Partial / Q000175:diagnosis* / Q000503:physiopathology; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000706:statistics & numerical data*; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood*; D013057:Spectrum Analysis / Q000706:statistics & numerical data
D010100:Oxygen