Comparative analysis of background EEG activity based on MRI findings in neonatal hypoxic-ischemic encephalopathy: a standardized, low-resolution, brain electromagnetic tomography (sLORETA) study

Abstract

Background: It is important to assess the degree of brain injury and predict long-term outcomes in neonates diagnosed with hypoxic-ischemic encephalopathy (HIE). However, routine studies, including magnetic resonance imaging (MRI) and conventional encephalography (EEG) or amplitude-integrated EEG (aEEG), have their own limitations in terms of availability and accuracy of evaluation. Recently, quantitative EEG (qEEG) has been shown to improve the predictive reliability of neonatal HIE and has been further refined with brain mapping techniques.

Methods: We investigated background EEG activities in 29 neonates with HIE who experienced therapeutic hypothermia, via qEEG using a distributed source model. MRI images were evaluated and classified into two groups (normal-to-mild injury vs moderate-to-severe injury), based on a scoring system. Non-parametric statistical analysis using standardized low-resolution brain electromagnetic tomography was performed to compare the current density distribution of four frequency bands (delta, theta, alpha, and beta) between the two groups.

Results: Electrical neuronal activities were significantly lower in the moderate-to-severe injury group compared with the normal-to-mild injury group. Background EEG activities in moderate-to-severe HIE were most significantly reduced in the temporal and parietal lobes. Quantitative EEG also revealed a decrease in background activity at all frequency bands, with a maximum in decrease in the delta component. The maximum difference in current density was found in the inferior parietal lobule of the right parietal lobe for the delta frequency band.

Conclusions: Our study demonstrated quantitative and topographical changes in EEG in moderate-to-severe neonatal HIE. They also suggest possible implementation and evaluation of conventional EEG and aEEG in neonatal HIE. The findings have implications as biomarkers in the assessment of neonatal HIE.

Keywords: Distributed source model; Hypoxic-ischemic encephalopathy (HIE); Quantitative electroencephalography (qEEG); Standardized low-resolution brain electromagnetic tomography (sLORETA).

Fig. 1

Statistical maps using standardized low-resolution brain electromagnetic tomography (sLORETA) of four frequency bands in the two groups (moderate-to-severe injury vs. normal-to-mild injury) were projected onto a three-dimensional fiducial brain cortex. Delta (a). Theta (b). Alpha (c). Beta (d). Non-parametric statistical analyses were performed to compare the current density distribution of the four frequency bands between the two groups. Log-F-ratio statistics were employed, and the color scale represents log-F-ratio values (threshold log-F-ratio =  ± 0.375, p < 0.05; threshold log-F-ratio =  ± 0.490, p < 0.01). A indicates anterior; P posterior, S superior, I inferior, L left, R right, B both, H hemisphere, V ventricle

Fig. 2

Statistical maps using standardized low-resolution brain electromagnetic tomography (sLORETA) of the four frequency bands in the two groups (moderate-to-severe injury vs. normal-to-mild injury) were projected onto a brain MRI template. Non-parametric statistical analyses were performed to compare the current density distributions of the four frequency bands between the two groups. Maximum current density differences were found in the right inferior parietal lobule for the delta frequency band (a), the right superior temporal gyrus for the theta frequency band (b), the right middle temporal gyrus for the alpha frequency band (c), and the right superior temporal gyrus for the beta frequency band (d). MNI coord denotes Montreal Neurological Institute coordinate; A anterior, P posterior, L left, R right