Enhanced Regional Functional Connectivity Indicates Seizure Onset Zone
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ORIGINAL PAPER
Enhanced Regional Functional Connectivity Indicates Seizure Onset Zone Jianpo Su1,2 · Nicolás von Ellenrieder2 · Dewen Hu1 · Jean Gotman2 Received: 10 February 2020 / Accepted: 11 May 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract This project aims to explore if stronger functional connectivity (FC) exists in the maximal BOLD response of EEG/fMRI analysis when it is concordant with seizure-onset-zone (SOZ). Twenty-six patients with drug-resistant focal epilepsy who had an EEG/fMRI and later underwent stereo-EEG implantation were included. Different types of IEDs were labeled in scalp EEG and IED-related maximal BOLD responses were evaluated separately, each constituting one study. After evaluating concordance between maximal BOLD and SOZ, twenty-seven studies were placed in the concordant group and eight in the discordant group. We evaluated the local connectivity and ipsilaterally distant connectivity difference between the maximal BOLD and the contralateral homotopic region. Significantly stronger local FC was found for the maximal BOLD in the concordant group (p 0.25) (Englot et al. 2015). This is the mean metric and it is designed to measure the average intensity of connectivity. We also calculated the sum of the functional connectivity value of voxels (with r > 0.25) in both distance
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Brain Topography
Fig. 1 The general pipeline of the study. a The anatomical images of patients were normalized to the Montreal Neurological Institute (MNI) space using an affine transformation. The transformation was then applied to the EEG/fMRI t-maps and fMRI images, which were previously coregistered to the individual anatomical images, hence the MNI coordinates of the peak voxels of maximal BOLD response were obtained. b The peak voxel of the primary cluster in the t-map of the EEG/fMRI analysis (The black dot in the upper image) and its contralateral homotopic voxel (The yellow dot in the lower image) were selected as the seeds. Local (connectivity to voxels within the sphere in solid line) and ipsilaterally distant (connectivity to ipsilateral voxels outside the sphere in dashed line) functional connectivity (FC) was defined and calculated. c Right-tail paired t-tests were
applied to see if there are stronger FC with the maximal BOLD than with its contralateral homotopic region using the mean metric and the sum metric at the group level. Comparison was done under four categories based on concordance between the maximal BOLD and seizure onset zone, together with the range of FC: concordant group—local connectivity, concordant group—ipsilaterally distant connectivity, discordant group—local connectivity, discordant group—ipsilaterally distant connectivity. d The original FC difference in each study was transformed to z-score using the distribution of the same between-hemisphere FC difference in healthy controls (HCP subjects). The z-score enabled us to determine if the FC difference was significantly larger than the control group in individual level
ranges (St
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