Functional connectivity of the irritative zone identified by electrical source imaging, and EEG-correlated fMRI analyses

Javier Urriola; Steffen Bollmann; Fred Tremayne; Hana Burianová; Lars Marstaller; David Reutens

doi:10.1016/j.nicl.2020.102440

Functional connectivity of the irritative zone identified by electrical source imaging, and EEG-correlated fMRI analyses

Neuroimage Clin. 2020:28:102440. doi: 10.1016/j.nicl.2020.102440. Epub 2020 Sep 18.

Authors

Javier Urriola¹, Steffen Bollmann², Fred Tremayne³, Hana Burianová⁴, Lars Marstaller⁴, David Reutens⁵

Affiliations

¹ Centre for Advanced Imaging, The University of Queensland, Brisbane, Australia.
² Centre for Advanced Imaging, The University of Queensland, Brisbane, Australia; ARC Training Centre for Innovation in Biomedical Imaging Technology, The University of Queensland, Brisbane, Australia.
³ Department of Neurology, Royal Brisbane and Women's Hospital, Australia.
⁴ Centre for Advanced Imaging, The University of Queensland, Brisbane, Australia; Department of Psychology, Bournemouth University, Bournemouth, United Kingdom.
⁵ Centre for Advanced Imaging, The University of Queensland, Brisbane, Australia; ARC Training Centre for Innovation in Biomedical Imaging Technology, The University of Queensland, Brisbane, Australia. Electronic address: d.reutens@uq.edu.au.

Abstract

Objective: The irritative zone - the area generating epileptic spikes - can be studied non-invasively during the interictal period using Electrical Source Imaging (ESI) and simultaneous electroencephalography-functional magnetic resonance imaging (EEG-fMRI). Although the techniques yield results which may overlap spatially, differences in spatial localization of the irritative zone within the same patient are consistently observed. To investigate this discrepancy, we used Blood Oxygenation Level Dependent (BOLD) functional connectivity measures to examine the underlying relationship between ESI and EEG-fMRI findings.

Methods: Fifteen patients (age 20-54), who underwent presurgical epilepsy investigation, were scanned using a single-session resting-state EEG-fMRI protocol. Structural MRI was used to obtain the electrode localisation of a high-density 64-channel EEG cap. Electrical generators of interictal epileptiform discharges were obtained using a distributed local autoregressive average (LAURA) algorithm as implemented in Cartool EEG software. BOLD activations were obtained using both spike-related and voltage-map EEG-fMRI analysis. The global maxima of each method were used to investigate the temporal relationship of BOLD time courses and to assess the spatial similarity using the Dice similarity index between functional connectivity maps.

Results: ESI, voltage-map and spike-related EEG-fMRI methods identified peaks in 15 (100%), 13 (67%) and 8 (53%) of the 15 patients, respectively. For all methods, maxima were localised within the same lobe, but differed in sub-lobar localisation, with a median distance of 22.8 mm between the highest peak for each method. The functional connectivity analysis showed that the temporal correlation between maxima only explained 38% of the variance between the time course of the BOLD response at the maxima. The mean Dice similarity index between seed-voxel functional connectivity maps showed poor spatial agreement.

Significance: Non-invasive methods for the localisation of the irritative zone have distinct spatial and temporal sensitivity to different aspects of the local cortical network involved in the generation of interictal epileptiform discharges.

Keywords: EEG-fMRI; Electrical source imaging; Focal epilepsy; Functional connectivity; Irritative zone.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Adult
Algorithms
Brain / diagnostic imaging
Brain Mapping
Electroencephalography
Epilepsy* / diagnostic imaging
Humans
Magnetic Resonance Imaging*
Middle Aged
Young Adult