The effect of reducing EEG electrode number on the visual interpretation of the human expert for neonatal seizure detection

Objectives: To measure changes in the visual interpretation of the EEG by the human expert for neonatal seizure detection when reducing the number of recording electrodes. Methods: EEGs were recorded from 45 infants admitted to the neonatal intensive care unit (NICU). Three experts annotated seizures in EEG montages derived from 19, 8 and 4 electrodes. Differences between annotations were assessed by comparing intra-montage with inter-montage agreement (K). Results: Three experts annotated 4464 seizures across all infants and montages. The inter-expert agreement was not significantly altered by the number of electrodes in the montage (p = 0.685, n = 43). Reducing the number of EEG electrodes altered the seizure annotation for all experts. Agreement between the 19-electrode montage (K-19,K-19 = 0.832) was significantly higher than the agreement between 19 and 8-electrode montages (dK = 0.114; p <0.001, n = 42) or 19 and 4-electrode montages (dK = 0.113, p <0.001, n = 43). Seizure burden and number were significantly underestimated by the 4 and 8-electrode montage (p <0.001). No significant difference in agreement was found between 8 and 4-electrode montages (dK = 0.002; p = 0.07, n = 42). Conclusions: Reducing the number of EEG electrodes from 19 electrodes resulted in slight but significant changes in seizure detection. (C) 2017 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.Peer reviewe

Analysis of infant cortical synchrony is constrained by the number of recording electrodes and the recording montage

Objective: To assess how the recording montage in the neonatal EEG influences the detection of cortical source signals and their phase interactions. Methods: Scalp EEG was simulated by forward modeling 20-200 simultaneously active sources covering the cortical surface of a realistic neonatal head model. We assessed systematically how the number of scalp electrodes (11-85), analysis montage, or the size of cortical sources affect the detection of cortical phase synchrony. Statistical metrics were developed for quantifying the resolution and reliability of the montages. Results: The findings converge to show that an increase in the number of recording electrodes leads to a systematic improvement in the detection of true cortical phase synchrony. While there is always a ceiling effect with respect to discernible cortical details, we show that the average and Laplacian montages exhibit superior specificity and sensitivity as compared to other conventional montages. Conclusions: Reliability in assessing true neonatal cortical synchrony is directly related to the choice of EEG recording and analysis configurations. Because of the high conductivity of the neonatal skull, the conventional neonatal EEG recordings are spatially far too sparse for pertinent studies, and this loss of information cannot be recovered by re-montaging during analysis. Significance: Future neonatal EEG studies will need prospective planning of recording configuration to allow analysis of spatial details required by each study question. Our findings also advice about the level of details in brain synchrony that can be studied with existing datasets or by using conventional EEG recordings. (C) 2015 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.Peer reviewe

Early brain activity : Translations between bedside and laboratory

Neural activity is both a driver of brain development and a readout of developmental processes. Changes in neuronal activity are therefore both the cause and consequence of neurodevelopmental compromises. Here, we review the assessment of neuronal activities in both preclinical models and clinical situations. We focus on issues that require urgent translational research, the challenges and bottlenecks preventing translation of biomedical research into new clinical diagnostics or treatments, and possibilities to overcome these barriers. The key questions are (i) what can be measured in clinical settings versus animal experiments, (ii) how do measurements relate to particular stages of development, and (iii) how can we balance practical and ethical realities with methodological compromises in measurements and treatments.Peer reviewe

Cortical responses to tactile stimuli in preterm infants

Abstract The conventional assessment of preterm somatosensory functions using averaged cortical responses to electrical stimulation ignores the characteristic components of preterm somatosensory evoked responses (SERs). Our study aimed to systematically evaluate the occurrence and development of SERs after tactile stimulus in preterm infants. We analysed SERs performed during 45 electroencephalograms (EEGs) from 29 infants at the mean post-menstrual age of 30.7 weeks. Altogether 2,087 SERs were identified visually at single trial level from unfiltered signals capturing also their slowest components. We observed salient SERs with a high amplitude slow component at a high success rate after hand (95%) and foot (83%) stimuli. There was a clear developmental change in both the slow wave and the higher frequency components of the SERs. Infants with intraventricular haemorrhage (IVH; eleven infants) had initially normal SERs, but those with bilateral IVH later showed a developmental decrease in the ipsilateral SER occurrence after 30 weeks of post-menstrual age. Our study shows that tactile stimulus applied at bedside elicits salient SERs with a large slow component and an overriding fast oscillation, which are specific to the preterm period. Prior experimental research indicates that such SERs allow studying both subplate and cortical functions. Our present findings further suggest that they might offer a window to the emergence of neurodevelopmental sequalae after major structural brain lesions and, hence, an additional tool for both research and clinical neurophysiological evaluation of infants before term age.Peer reviewe

EARLY DEVELOPMENT OF SYNCHRONY IN CORTICAL ACTIVATIONS IN THE HUMAN

Peer reviewe

A comparative study of electrical potential sensors and Ag/AgCl electrodes for characterising spontaneous and event related electroencephalagram signals

For exactly 90 years researchers have used electroencephalography (EEG) as a window into the activities of the brain. Even now its high temporal resolution coupled with relatively low cost compares favourably to other neuroimaging techniques such as magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI). For the majority of this time the standard electrodes used for non-invasive monitoring of electrical activities of the brain have been Ag/AgCl metal electrodes. Although these electrodes provide a reliable method for recording EEG they suffer from noise, such as offset potential drift, and usability issues, for example, difficult skin preparation and cross-coupling of adjacent electrodes. In order to tackle these issues a prototype Electric Potential Sensor (EPS) device based on an auto-zero operational amplifier has been developed and evaluated. The absence of 1/f noise in these devices makes them ideal for use with signal frequencies of ~10 Hz or less. The EPS is a novel active ultrahigh impedance capacitively coupled sensor. The active electrodes are designed to be physically and electrically robust and chemically and biochemically inert. They are electrically insulated (anodized) and scalable. A comprehensive study was undertaken to compare the results of neural signals recorded by the EPS with a standard commercial EEG system. These studies comprised measurements of both free running EEG and Event Related Potentials (ERPs). Results demonstrate that the EPS provides a promising alternative, with many added benefits compared to standard EEG sensors, including reduced setup time, elimination of sensor cross-coupling, lack of a ground electrode and distortion of electrical potentials encountered when using standard gel electrodes. Quantitatively, highly similar signals were observed between the EPS and EEG sensors for both free running and evoked brain activity with cross correlations of higher than 0.9 between the EPS and a standard benchmark EEG system. Future developments of EPS-based neuroimaging include the implementation of a whole head ultra-dense EPS array, and the mapping of distributions of scalp recorded electrical potentials remotely

Hybrid head cap for mouse brain studies

Abstract. In this thesis, I present a hybrid head cap in combination with non-invasive multi-channel Electroencephalogram (EEG) and Near-Infrared Spectroscopy (NIRS) to measure brainwaves on mice’s scalps. Laboratory animal research provides insights into multiple potential applications involving humans and other animals. An experimental framework that targets laboratory animals can lead to useful transnational research if it strongly reflects the actual application environment. The non-invasive head cap with three electrodes for EEG and two optodes for NIRS is suggested to measure brainwaves throughout the laboratory mice’s entire brain region without surgical procedures. The suggested hybrid head cap aims to ensure stability in vivo monitoring for mouse brain in a non-invasive way, similarly as the monitoring is performed for the human brain. The experimental part of the work to study the quality of the gathered EEG and fNIRS signals, and usability validation of the head cap, however, was not completed in the planned time frame of the thesis work

Brain connectivity in preterm infants

Preterm infants are at increased risk for neurological disabilities and cognitive dysfunction at later age. Electroencephalography (EEG) is a useful method for assessing neurological function and prognosis. In the very preterm infant (below 32 weeks gestation), the EEG background activity is characterized by discontinuity, instability and fragmentation. With advancing age this background becomes more continuous. EEG spectral power analyses in very preterm infants show a maturational change from high-amplitude low-frequency waves to low-amplitude high-frequency waves. The frequency spectrum of an EEG is divided in ?newborn(0-2 Hz), ?newborn (2-6 Hz), ?newborn (6-13 Hz) and ?newborn (13-30 Hz) band. Hence, in preterm infants EEG spectral power decreases with age, with a shift from the lower (delta) to the higher frequency (alpha, beta) content of the EEG. During normal maturation different developmental processes occur in the anatomy, e.g. myelination and formation of interneural connections. The main anatomical structures enabling connections between the hemispheres are the corpus callosum (the direct highway between left and right hemispheres) and thalamo-cortical connections (the local secondary roadmap between the hemispheres with subcortical deeper brain structures as interface). Increased anatomical connectivity between brain areas may result in more functional connectivity, assessed by EEG signal shape similarity between brain regions. The goal of this thesis was to quantify the neuronal connectivity as a function of postmenstrual age (PMA). EEG cross-correlation analyses between homologous channels of brain hemispheres were calculated to study the peak correlation value and corresponding lag time as function of PMA.In this study 36 preterm neonates with appropriate weight for gestation and a normal follow-up at the age of five years were included. For comparison a set of 9 preterm infants with abnormal neurological follow-up was included. Beside these infants, two infants were studied with no interhemispherical connection between the hemispheres, a condition known as agenesis of the corpus callosum.The neonatal EEGs were obtained by the end of the first week of life. The reduced 10-20 EEG montage system was used for measuring the EEGs. Five bipolar channels at homologous positions on both brain hemispheres were used for the cross-correlation analysis. Each EEG recording was divided into 8 second epochs, in which for every epoch, the maximum correlation value and corresponding lag time was determined. In each EEG recording, the median correlation and time lag value was calculated from the 8 second epochs. Linear regression analysis was used to study the influence of postmenstrual age on the time domain parameters. The correlation values significantly decreased with increasing PMA for all the channels. With increasing PMA, three of the five bipolar channels showed a significant change in lag time. The frontal-temporal channel showed an increase, while the other temporal channels showed a decrease as a function of PMA. Cross-correlation analysis showed no difference in preterm infants with normal and abnormal follow-up. Correlation values and lag time of the two infants with corpus callosum agenesis were comparable with the other subjects. For all spectral power frequency, the correlation values decreased with PMA. For higher frequency bands the correlation values were lower. The observed trend for the burst showed a similar trend as the whole EEG. We observed a significant decrease of the correlation values for all channels, indicating a loss of similarity in signal shape. No uniform change was observed for the corresponding time lag, indicating no uniform changes in signal conductivity. No distinction could be made between infants with an intact or absent corpus callosum. This may indicate that interhemispherical EEG cross-correlation is not influenced by the presence of a corpus callosum and that other circuitries are involved. Head growth (increasing electrode position) only partially explains the lag time changes we observed. A limitation of the methodology is the low spatial resolution in EEG electrode position. We speculate that the complex process of maturation in preterm infants, including myelination, increasing interneural connections, development excitatory and inhibitory circuitries lead to a complex signal feedback system that may be more important than just the direct interhemispherical connection. Preterm infants are at increased risk for neurological disabilities and cognitive dysfunction at later age. Electroencephalography (EEG) is a useful method for assessing neurological function and prognosis. In the very preterm infant (below 32 weeks gestation), the EEG background activity is characterized by discontinuity, instability and fragmentation. With advancing age this background becomes more continuous. EEG spectral power analyses in very preterm infants show a maturational change from high-amplitude low-frequency waves to low-amplitude high-frequency waves. The frequency spectrum of an EEG is divided in ?newborn(0-2 Hz), ?newborn (2-6 Hz), ?newborn (6-13 Hz) and ?newborn (13-30 Hz) band. Hence, in preterm infants EEG spectral power decreases with age, with a shift from the lower (delta) to the higher frequency (alpha, beta) content of the EEG. During normal maturation different developmental processes occur in the anatomy, e.g. myelination and formation of interneural connections. The main anatomical structures enabling connections between the hemispheres are the corpus callosum (the direct highway between left and right hemispheres) and thalamo-cortical connections (the local secondary roadmap between the hemispheres with subcortical deeper brain structures as interface). Increased anatomical connectivity between brain areas may result in more functional connectivity, assessed by EEG signal shape similarity between brain regions. The goal of this thesis was to quantify the neuronal connectivity as a function of postmenstrual age (PMA). EEG cross-correlation analyses between homologous channels of brain hemispheres were calculated to study the peak correlation value and corresponding lag time as function of PMA.In this study 36 preterm neonates with appropriate weight for gestation and a normal follow-up at the age of five years were included. For comparison a set of 9 preterm infants with abnormal neurological follow-up was included. Beside these infants, two infants were studied with no interhemispherical connection between the hemispheres, a condition known as agenesis of the corpus callosum.The neonatal EEGs were obtained by the end of the first week of life. The reduced 10-20 EEG montage system was used for measuring the EEGs. Five bipolar channels at homologous positions on both brain hemispheres were used for the cross-correlation analysis. Each EEG recording was divided into 8 second epochs, in which for every epoch, the maximum correlation value and corresponding lag time was determined. In each EEG recording, the median correlation and time lag value was calculated from the 8 second epochs. Linear regression analysis was used to study the influence of postmenstrual age on the time domain parameters. The correlation values significantly decreased with increasing PMA for all the channels. With increasing PMA, three of the five bipolar channels showed a significant change in lag time. The frontal-temporal channel showed an increase, while the other temporal channels showed a decrease as a function of PMA. Cross-correlation analysis showed no difference in preterm infants with normal and abnormal follow-up. Correlation values and lag time of the two infants with corpus callosum agenesis were comparable with the other subjects. For all spectral power frequency, the correlation values decreased with PMA. For higher frequency bands the correlation values were lower. The observed trend for the burst showed a similar trend as the whole EEG. We observed a significant decrease of the correlation values for all channels, indicating a loss of similarity in signal shape. No uniform change was observed for the corresponding time lag, indicating no uniform changes in signal conductivity. No distinction could be made between infants with an intact or absent corpus callosum. This may indicate that interhemispherical EEG cross-correlation is not influenced by the presence of a corpus callosum and that other circuitries are involved. Head growth (increasing electrode position) only partially explains the lag time changes we observed. A limitation of the methodology is the low spatial resolution in EEG electrode position. We speculate that the complex process of maturation in preterm infants, including myelination, increasing interneural connections, development excitatory and inhibitory circuitries lead to a complex signal feedback system that may be more important than just the direct interhemispherical connection