Effects of uncertainty in head tissue conductivity and complexity on EEG forward modeling in neonates

Abstract

In this study, we investigated the impact of uncertainty in head tissue conductivities and inherent geometrical complexities including fontanels in neonates. Based on MR and CT coregistered images, we created a realistic neonatal head model consisting of scalp, skull, fontanels, cerebrospinal fluid (CSF), gray matter (GM), and white matter (WM). Using computer simulations, we investigated the effects of exclusion of CSF and fontanels, discrimination between GM and WM, and uncertainty in conductivity of neonatal head tissues on EEG forward modeling. We found that exclusion of CSF from the head model induced the strongest widespread effect on the EEG forward solution. Discrimination between GM and white matter also induced a strong widespread effect, but which was less intense than that of CSF exclusion. The results also showed that exclusion of the fontanels from the neonatal head model locally affected areas beneath the fontanels, but this effect was much less pronounced than those of exclusion of CSF and GM/WM discrimination. Changes in GM/WM conductivities by 25% with respect to reference values induced considerable effects in EEG forward solution, but this effect was more pronounced for GM conductivity. Similarly, changes in skull conductivity induced effects in the EEG forward modeling in areas covered by the cranial bones. The least intense effect on EEG was caused by changes in conductivity of the fontanels. Our findings clearly emphasize the impact of uncertainty in conductivity and deficiencies in head tissue compartments on modeling research and localization of brain electrical activity in neonates. Hum Brain Mapp 37:3604-3622, 2016. © 2016 Wiley Periodicals, Inc.

The effect of stimulation type, head modeling, and combined EEG and MEG on the source reconstruction of the somatosensory P20/N20 component

“…This is due to the absence of the highly conductive CSF compartment and the homogenization of the conductivity in the source space area in the realistically shaped 3CI head model (see Figure 3). Similar conductivity sensitivity effects have been found previously using either the FEM or the finite difference method (FDM; Gençer & Acar, 2004;Ramon et al, 2004;Wendel et al, 2008;Vallaghé & Clerc, 2009;Vorwerk et al, 2014Vorwerk et al, , 2019Azizollahi et al, 2016;Cuartas et al, 2019). Our results, therefore, support the importance of more realistic modeling of these inner brain tissue compartments that also strongly influence than the estimated individual conductivity parameters for the skull layer, as also shown by (Aydin et al, 2014;Fernández-Corazza et al, 2017).…”

“…Based on MRI data, conventional approaches segment the head into scalp, skull and brain, resulting in a realisticallyshaped three-compartment isotropic (3CI) head model (Brette & Destexhe, 2012;Fuchs et al, 1998;Huang et al, 2007;Kybic et al, 2005;Stenroos & Nummenmaa, 2016). More detailed approaches segment the brain further into cerebrospinal fluid [CSF], gray [GM] and white matter [WM], and/or the skull into compacta (SC) and spongiosa (SS; Ramon, Schimpf, & Haueisen, 2004;Akalin Acar & Makeig, 2013;Rice et al, 2012;Montes-Restrepo et al, 2014;Azizollahi, Aarabi, & Wallois, 2016;Cuartas, Acosta-Medina, Castellanos-Dominguez, & Mantini, 2019). Moreover, brain anisotropy can be incorporated by using diffusion tensor imaging (DTI) data (Tuch, Wedeen, Dale, George, & Belliveau, 2001;Güllmar, Haueisen, & Reichenbach, 2010;Ruthotto et al, 2011;Cuartas et al, 2019), resulting in six compartment anisotropic (6CA) head models (Aydin et al, 2014;Vorwerk et al, 2014).…”

Plasticity of neonatal neuronal networks in very premature infants: Source localization of temporal theta activity, the first endogenous neural biomarker, in temporoparietal areas

“…Group 1 consisted of infants between 26 and 30 wGA and group 2 consisted of infants between 30 and 32 wGA. Parallel studies conducted in the laboratory [Azizollahi et al, 2016] suggest that the incorporation of a CSF layer is essential in premature infants, as in adults [Ramon et al, 2004;Rice et al, 2013;Vallaghe and Clerc, 2009;Vorwerk et al, 2014]. These realistic head models were obtained by segmentation of the various layers in order to delineate the 'air-scalp', 'scalp-skull' and 'skull-brain' interfaces [see Roche-Labarbe et al, 2008 for the segmentation method].…”

“…To (30 wGA)]. As the impact of the fontanelle is considered to be relatively limited away from the fontanelles [Azizollahi et al, 2016;Gargiulo et al, 2015;Lew et al, 2013;Roche-Labarbe et al, 2008], the fontanelles were not included in our model. The various tissues were identified by segmentation using a combination of greyscale thresholding and a region growing algorithm plus three operators: opening, closing, dilation.…”

“…The CSF is an important layer both in adults [Ramon et al, 2004;Rice et al, 2013;Vallaghe and Clerc, 2009;Vorwerk et al, 2014] and in term neonates [Azizollahi et al, 2016] and probably has a major impact on source localization. To check for errors of source localization related to the use of a 3-layer head model without CSF, a 4-layer head model was computed from the same 3D head model (UCL Head model).…”