Simultaneous intracranial EEG and fMRI of interictal epileptic discharges in humans

Vulliémoz, Serge; Carmichael, David W.; Rosenkranz, Karin; Diehl, Beate; Rodionov, Roman; Walker, Matthew C.; McEvoy, Andrew W.; Lemieux, Louis

doi:10.1016/j.neuroimage.2010.08.004

Cited by 128 publications

(112 citation statements)

References 39 publications

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“…Such high frequencies (i.e., small inter-spike intervals) may indeed occur in epileptiform EEG signals, particularly in children (Jacobs et al 2008). They have also been shown in a recent simultaneous intracranical EEG-fMRI study (Vulliemoz et al 2011). Preliminary results indicated that the BOLD signal shows two distinct regimes in terms of sub-and supralinear behavior.…”

Section: Methodssupporting

confidence: 62%

Modeling of the Neurovascular Coupling in Epileptic Discharges

et al. 2011

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Despite the interest in simultaneous EEG-fMRI studies of epileptic spikes, the link between epileptic discharges and their corresponding hemodynamic responses is poorly understood. In this context, biophysical models are promising tools for investigating the mechanisms underlying observed signals. Here, we apply a metabolic-hemodynamic model to simulated epileptic discharges, in part generated by a neural mass model. We analyze the effect of features specific to epileptic neuronal activity on the blood oxygen level dependent (BOLD) response, focusing on the issues of linearity in neurovascular coupling and on the origin of negative BOLD signals. We found both sub- and supra-linearity in simulated BOLD signals, depending on whether one observes the early or the late part of the BOLD response. The size of these non-linear effects is determined by the spike frequency, as well as by the amplitude of the excitatory activity. Our results additionally indicate a minor deviation from linearity at the neuronal level. According to a phase space analysis, the possibility to obtain a negative BOLD response to an epileptic spike depends on the existence of a long and strong excitatory undershoot. Moreover, we strongly suggest that a combined EEG-fMRI modeling approach should include spatial assumptions. The present study is a step towards an increased understanding of the link between epileptic spikes and their BOLD responses, aiming to improve the interpretation of simultaneous EEG-fMRI recordings in epilepsy.

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Section: Methodssupporting

confidence: 62%

Modeling of the Neurovascular Coupling in Epileptic Discharges

et al. 2011

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“…The BOLD signal usually increases in regions generating focal IEDs, 3 but often in the context of more widespread, or even distant, responses. 4 Simultaneous intracranial EEG/fMRI recordings 5 have shown IED-related BOLD changes in the immediate vicinity of the intracranial EEG focus, confirming spatial concordance between neuronal and BOLD changes. Distant BOLD changes related to specific IED patterns were also observed.…”

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confidence: 71%

Contribution of EEG/fMRI to the definition of the epileptic focus

Pittau

Dubeau²,

Gotman³

2012

Neurology

110

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Objectives:To evaluate the clinical relevance of EEG/fMRI in patients with focal epilepsy, by assessing the information it adds to the scalp EEG in the definition of the epileptic focus. Methods:Forty-three patients with focal epilepsy were studied with EEG/fMRI using a 3-T scanner. Blood oxygen levelϪdependent (BOLD) signal changes related to interictal epileptic discharges (IEDs) were classified as concordant or not concordant with the scalp EEG spike field and as contributory if the BOLD signal provided additional information to the scalp EEG about the epileptic focus or not contributory if it did not. We considered patients having intracerebral EEG or a focal lesion on MRI as having independent validation.Results: Thirty-three patients had at least 3 IEDs during the EEG/fMRI acquisition (active EEG), and all had a BOLD response. In 29 of 33 (88%) patients, the BOLD response was concordant, and in 21 of 33 (64%) patients, the BOLD response was contributory. Fourteen patients had an independent validation: in 12 of these 14, the BOLD responses were validated and in 2 they were invalidated. Conclusions:A BOLD response was present in all patients with active EEG, and more specific localization of the epileptic focus was gained from EEG/fMRI in half of the patients who were scanned, when compared with scalp EEG alone. This study demonstrates that EEG/fMRI, in the context of a clinical practice, may contribute to the localization of the interictal epileptic generator in patients with focal epilepsy. Neurology ® 2012;78:1479-1487 GLOSSARY BOLD ϭ blood oxygen levelϪdependent; EPI ϭ echoplanar imaging; FCD ϭ focal cortical dysplasia; IED ϭ interictal epileptic discharge; MTS ϭ mesial temporal lobe sclerosis; SEEG ϭ stereo-EEG; TE ϭ echo time; TR ϭ repetition time.Recording fMRI and EEG simultaneously is a noninvasive method detecting cerebral hemodynamic changes related to interictal epileptic discharges (IEDs) on scalp EEG. Several studies demonstrated the ability of EEG/fMRI to characterize various forms of focal and generalized epilepsy.1,2 In patients with focal epilepsy, especially those who are pharmacoresistant and surgical candidates, the significant clinical question is how the blood oxygenation levelϪde-pendent (BOLD) changes related to IEDs can contribute to localize the epileptic focus. The BOLD signal usually increases in regions generating focal IEDs, 3 but often in the context of more widespread, or even distant, responses.4 Simultaneous intracranial EEG/fMRI recordings 5 have shown IED-related BOLD changes in the immediate vicinity of the intracranial EEG focus, confirming spatial concordance between neuronal and BOLD changes. Distant BOLD changes related to specific IED patterns were also observed. EEG/fMRI may help in the evaluation of patients who are candidates for surgery 6 and, in patients with nonlesional frontal lobe epilepsy, EEG/fMRI contributed to localize foci subsequently confirmed by other imaging modalities or pathology.7 Finally, in a postsurgical population, it was shown that...

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“…Simultaneous recordings of fMRI and intracortical neural signals have shown correlations between the BOLD signal changes measured by fMRI and the activity of the main generators of the EEG signals (Logothetis et al, 2001). Safety concerns of icEEG-fMRI have been addressed and pioneering studies in recent years (e.g., Vulliemoz et al, 2011) have been conducted where the icEEG-fMRI results were either in agreement with icEEG results or concordant with MEG results. More icEEG-fMRI studies with larger sample size might be needed to explore the value, advantages and disadvantages of this invasive approach.…”

Section: Discussionmentioning

confidence: 99%