Maturation of cerebral electrical activity and development of cortical folding in young very preterm infants

Functional brain activity is highly associated with cortical myelination in neonates

Functional organization of the human cerebral cortex is highly constrained by underlying brain structures, but how functional activity is associated with different brain structures during development is not clear, especially at the neonatal stage. Since long-range functional connectivity is far from mature in the dynamically developing neonatal brain, it is of great scientific significance to investigate the relationship between different structural and functional features at the local level. To this end, for the first time, correlation and regression analyses were performed to examine the relationship between cortical morphology, cortical myelination, age, and local brain functional activity, as well as functional connectivity strength using high-resolution structural and resting-state functional MRI data of 177 neonates (29-44 postmenopausal weeks, 98 male and 79 female) from both static and dynamic perspectives. We found that cortical myelination was most strongly associated with local brain functional activity across the cerebral cortex than other cortical structural features while controlling the age effect. These findings suggest the crucial role of cortical myelination in local brain functional development at birth, providing valuable insights into the fundamental biological basis of functional activity at this early developmental stage.

CARFS7: A guide and proforma for reading a preterm neonate's EEG

OBJECTIVES

The important role of the EEG in preterm and term babies in investigating brain function and seizures, predicting outcomes, evaluating therapeutic interventions and decision-making is being increasingly acknowledged. Development of the brain in the last trimester of pregnancy results in rapid changes in the EEG patterns in this period. Acquiring and interpreting the EEG of a preterm baby can be challenging. The aim of this study was to develop a proforma titled CARFS⁷ (Continuity, Amplitude, Reactivity, Frequency, Synchrony, Symmetry, Sleep, Sharps, Shapes, Size and Seizures) to enable neurologists to read EEGs of premature babies with greater confidence, ease and accuracy and produce a report more easily repeatable and homogenous among operators.

METHODS

The CARFS⁷proforma was developed based on a literature review and the personal experience of the authors. The parameters of the EEG evaluated and scored in the proforma are Continuity, Amplitude, Reactivity/Variability, Frequency, Synchrony, Symmetry, Sleep, Sharps, Shapes/Patterns, Size and Seizures. We also assessed the interrater reliability of the proposed scoring system incorporated in the proforma.

RESULTS

CARFS⁷ proforma incorporates a number of parameters that help evaluate the preterm EEG. The interrater reliability of the proposed scoring system in the CARFS⁷proforma was high.

CONCLUSIONS

CARFS⁷ is a user friendly proforma for reading EEGs in the preterm infant. Interrater reliability using Cohen's k shows high agreement between two child neurologists who independently rated the EEGs of 25 premature babies using this proforma. CARFS⁷ has the potential to provide, accurate, reproducible and valuable information on brain function in the preterm infant in clinical practice.

Normal EEG during the neonatal period: maturational aspects from premature to full-term newborns

Electroencephalography (EEG) is the reference tool for the analysis of brain function, reflecting normal and pathological neuronal network activity. During the neonatal period, EEG patterns evolve weekly, according to gestational age. The first analytical criteria for the various maturational stages and standardized neonatal EEG terminology were published by a group of French neurophysiologists training in Paris (France) in 1999. These criteria, defined from analog EEG, were completed in 2010 with digital EEG analysis. Since then, this work has continued, aided by the technical progress in EEG acquisition, the improvement of knowledge on the maturating processes of neuronal networks, and the evolution of critical care. In this review, we present an exhaustive and didactic overview of EEG characteristics from extremely premature to full-term infants. This update is based on the scientific literature, enhanced by the study of normal EEGs of extremely premature infants by our group of neurophysiologists. For educational purposes, particular attention has been paid to illustrations using new digital tools.

Automated cot-side tracking of functional brain age in preterm infants

Objective

A major challenge in the care of preterm infants is the early identification of compromised neurological development. While several measures are routinely used to track anatomical growth, there is a striking lack of reliable and objective tools for tracking maturation of early brain function; a cornerstone of lifelong neurological health. We present a cot‐side method for measuring the functional maturity of the newborn brain based on routinely available neurological monitoring with electroencephalography (EEG).

Methods

We used a dataset of 177 EEG recordings from 65 preterm infants to train a multivariable prediction of functional brain age (FBA) from EEG. The FBA was validated on an independent set of 99 EEG recordings from 42 preterm infants. The difference between FBA and postmenstrual age (PMA) was evaluated as a predictor for neurodevelopmental outcome.

Results

The FBA correlated strongly with the PMA of an infant, with a median prediction error of less than 1 week. Moreover, individual babies follow well‐defined individual trajectories. The accuracy of the FBA applied to the validation set was statistically equivalent to the training set accuracy. In a subgroup of infants with repeated EEG recordings, a persistently negative predicted age difference was associated with poor neurodevelopmental outcome.

Interpretation

The FBA enables the tracking of functional neurodevelopment in preterm infants. This establishes proof of principle for growth charts for brain function, a new tool to assist clinical management and identify infants who will benefit most from early intervention.

Assessment of neonatal EEG background and neurodevelopment in full-term small for their gestational age infants

BACKGROUND

Delayed brain function development in small-gestational-age (SGA) infants has been reported. We aimed to quantify rates of immature neonatal EEG patterns and their association with neurodevelopment in SGA full-term neonates.

METHODS

Using a cohort design, 50 SGA (birthweight <10th percentile) and 44 appropriate-gestational-age (AGA) term neonates underwent continuous video-EEG recordings lasting >3 h. Seventy-three of them were assessed at 2-years-old using Bayley-III-Scales. For EEG analysis, several segments of discontinuous/alternating EEG tracings were selected.

MAIN OUTCOMES MEASURED

(1) Visual analysis (patterns of EEG maturity); (2) Power spectrum in δ, θ, α and β frequency bands; and (3) scores in motor, cognitive and language development.

RESULTS

(1) SGA infants, compared to AGA, showed: (a) higher percentages of discontinuous EEG, both asynchrony and interhemispheric asymmetry, and bursts with delta-brushes, longer interburst-interval duration and more transients/hour; (b) lower relative power spectrum in δ and higher in α; and (c) lower scores on motor, language and cognitive neurodevelopment. (2) Asymmetry >5%, interburst-interval >5 s, discontinuity >11%, and bursts with delta-brushes >11% were associated with lower scores on Bayley-III.

CONCLUSIONS

In this prospective study, SGA full-term neonates showed high rates of immature EEG patterns. Low-birthweight and immaturity EEG were both correlated with low development scores.

How Early Can a Seizure Happen? Pathophysiological Considerations of Extremely Premature Infant Brain Development

Seizures in neonates represent a neurologic emergency requiring prompt recognition, determination of etiology, and treatment. Yet, the definition and identification of neonatal seizures remain challenging and controversial, in part due to the unique physiology of brain development at this life stage. These issues are compounded when considering seizures in premature infants, in whom the complexities of brain development may engender different clinical and electrographic seizure features at different points in neuronal maturation. In extremely premature infants (< 28 weeks gestational age), seizure pathophysiology has not been explored in detail. This review discusses the physiological and structural development of the brain in this developmental window, focusing on factors that may lead to seizures and their consequences at this early time point. We hypothesize that the clinical and electrographic phenomenology of seizures in extremely preterm infants reflects the specific pathophysiology of brain development in that age window.

Changes in brain morphology and microstructure in relation to early brain activity in extremely preterm infants

Background and ObjectiveTo investigate the relation of early brain activity with structural (growth of the cortex and cerebellum) and white matter microstructural brain development.MethodsA total of 33 preterm neonates (gestational age 26±1 weeks) without major brain abnormalities were continuously monitored with electroencephalography during the first 48 h of life. Rate of spontaneous activity transients per minute (SAT rate) and inter-SAT interval (ISI) in seconds per minute were calculated. Infants underwent brain magnetic resonance imaging ∼30 (mean 30.5; min: 29.3-max: 32.0) and 40 (41.1; 40.0-41.8) weeks of postmenstrual age. Increase in cerebellar volume, cortical gray matter volume, gyrification index, fractional anisotropy (FA) of posterior limb of the internal capsule, and corpus callosum (CC) were measured.ResultsSAT rate was positively associated with cerebellar growth (P=0.01), volumetric growth of the cortex (P=0.027), increase in gyrification (P=0.043), and increase in FA of the CC (P=0.037). ISI was negatively associated with cerebellar growth (P=0.002).ConclusionsIncreased early brain activity is associated with cerebellar and cortical growth structures with rapid development during preterm life. Higher brain activity is related to FA microstructural changes in the CC, a region responsible for interhemispheric connections. This study underlines the importance of brain activity for microstructural brain development.

Newborn Brain Function Is Affected by Fetal Exposure to Maternal Serotonin Reuptake Inhibitors

Recent experimental animal studies have shown that fetal exposure to serotonin reuptake inhibitors (SRIs) affects brain development. Modern recording methods and advanced computational analyses of scalp electroencephalography (EEG) have opened a possibility to study if comparable changes are also observed in the human neonatal brain. We recruited mothers using SRI during pregnancy (n = 22) and controls (n = 62). Mood and anxiety of mothers, newborn neurology, and newborn cortical function (EEG) were assessed. The EEG parameters were compared between newborns exposed to drugs versus controls, followed by comparisons of newborn EEG features with maternal psychiatric assessments. Neurological assessment showed subtle abnormalities in the SRI-exposed newborns. The computational EEG analyses disclosed a reduced interhemispheric connectivity, lower cross-frequency integration, as well as reduced frontal activity at low-frequency oscillations. These effects were not related to maternal depression or anxiety. Our results suggest that antenatal serotonergic treatment might change newborn brain function in a manner compatible with the recent experimental studies. The present EEG findings suggest links at the level of neuronal activity between human studies and animal experiments. These links will also enable bidirectional translation in future studies on the neuronal mechanisms and long-term neurodevelopmental effects of early SRI exposure.

Convergence of BOLD and ERP measures of neural reactivity to emotional faces in children and adolescents with and without anxiety disorders

The neural bases of emotion are commonly measured using blood-oxygen-level-dependent (BOLD) signal and the late positive potential (LPP) event-related potential (ERP) component, but rarely together in the same individuals. Despite evidence of developmental changes in processing socio-emotional signals (e.g., faces) as reflected by both BOLD and LPP indices of brain maturation, the literature on the correspondence between these measures is limited to healthy adults, leaving questions regarding such correspondence across development and in clinical populations unaddressed. We examined the relationship between BOLD and LPP during an emotional face processing task in a large sample of youth (N = 70; age 7-19 years) with and without anxiety disorders, and tested whether BOLD signal in regions corresponding to LPP may account for age-related decreases in LPP. Greater activation in bilateral inferior frontal gyrus (IFG)/orbitofrontal gyrus (OFG), left supplementary motor area, right superior parietal lobule, and bilateral amygdala correlated with enhanced LPP to emotional faces in both anxious and healthy youth. Older youth exhibited reduced activation in bilateral IFG/OFG and bilateral amygdala, as well as reduced LPP. Decreased right IFG/OFG activation mediated the association between age and LPP. These findings support correspondence between these measures and need for multi-method approaches and indicate that age-related decreases in LPP may be driven, in part, by decreased IFG/OFG activation.

A review of important electroencephalogram features for the assessment of brain maturation in premature infants

This review describes the maturational features of the baseline electroencephalogram (EEG) in the neurologically healthy preterm infant. Features such as continuity, sleep state, synchrony and transient waveforms are described, even from extremely preterm infants and includes abundant illustrated examples. The physiological significance of these EEG features and their relationship to neurodevelopment are highlighted where known. This review also demonstrates the importance of multichannel conventional EEG monitoring for preterm infants as many of the features described are not apparent if limited channel EEG monitors are used.

CONCLUSION

This review aims to provide healthcare professionals in the neonatal intensive care unit with guidance on the more common normal maturational features seen in the EEG of preterm infants.

The suppression curve as a quantitative approach for measuring brain maturation in preterm infants

OBJECTIVES

We apply the suppression curve (SC) as an automated approach to describe the maturational change in EEG discontinuity in preterm infants. This method allows to define normative values of interburst intervals (IBIs) at different postmenstrual ages (PMA).

METHODS

Ninety-two multichannel EEG recordings from 25 preterm infants (born ⩽32weeks) with normal developmental outcome at 9months, were first analysed using the Line Length method, an established method for burst detection. Subsequently, the SC was defined as the 'level of EEG discontinuity'. The mean and the standard deviation of the SC, as well as the IBIs from each recording were calculated and correlated with PMA.

RESULTS

Over the course of development, there is a decrease in EEG discontinuity with a strong linear correlation between the mean SC and PMA till 34weeks. From 30weeks PMA, differences between discontinuous and continuous EEG become smaller, which is reflected by the decrease of the standard deviation of the SC. IBIs are found to have a significant correlation with PMA.

CONCLUSIONS

Automated detection of individual maturational changes in EEG discontinuity is possible with the SC. These changes include more continuous tracing, less amplitude differences and shorter suppression periods, reflecting development of the vigilance states.

SIGNIFICANCE

The suppression curve facilitates automated assessment of EEG maturation. Clinical applicability is straight forward since values for IBIs according to PMA are generated automatically.

Automatic measurement of interburst interval in premature neonates using range EEG

OBJECTIVE

To explore the direct measure of EEG amplitude (range EEG, rEEG) for detection of interburst intervals (IBIs) and bursts in neonates.

METHODS

Previously described 177 two-channel EEG recordings 3-6h long from 26 preterm infants (median gestational age of 26 weeks) at 23-38 weeks post-menstrual age (PMA) without major abnormalities were used to test four definitions of IBI detection algorithms with various settings of the parameters.

RESULTS

As the basis for all four algorithms we developed the aggregation of rEEG signal over the channels by taking its maximum, and method of EEG trace selection at different phases of sleep-wake cycle (with different degree of discontinuity). The two less restrictive algorithms - with one and two amplitude thresholds - turned to be the most promising definitions. There were enough IBI detections for analysis, with no substantial difference in mean and maximum values of intervals. The longest IBI were measured at the location of greater discontinuity. Values of bursts and IBI indices as well as association with PMA were close to the published normative values derived manually.

CONCLUSIONS

rEEG as a direct measure of EEG amplitude can be used for detection of bursts and IBI.

SIGNIFICANCE

The automatic measurement of IBI based on rEEG provides a basis for improvements in neonatal brain monitoring.

Evaluation of automatic feature detection algorithms in EEG: application to interburst intervals

In this paper, we present a new method to compare and improve algorithms for feature detection in neonatal EEG. The method is based on the algorithm׳s ability to compute accurate statistics to predict the results of EEG visual analysis. This method is implemented inside a Java software called EEGDiag, as part of an e-health Web portal dedicated to neonatal EEG. EEGDiag encapsulates a component-based implementation of the detection algorithms called analyzers. Each analyzer is defined by a list of modules executed sequentially. As the libraries of modules are intended to be enriched by its users, we developed a process to evaluate the performance of new modules and analyzers using a database of expertized and categorized EEGs. The evaluation is based on the Davies-Bouldin index (DBI) which measures the quality of cluster separation, so that it will ease the building of classifiers on risk categories. For the first application we tested this method on the detection of interburst intervals (IBI) using a database of 394 EEG acquired on premature newborns. We have defined a class of IBI detectors based on a threshold of the standard deviation on contiguous short time windows, inspired by previous work. Then we determine which detector and what threshold values are the best regarding DBI, as well as the robustness of this choice. This method allows us to make counter-intuitive choices, such as removing the 50 Hz filter (power supply) to save time.

Early Brain Activity Relates to Subsequent Brain Growth in Premature Infants

Recent experimental studies have shown that early brain activity is crucial for neuronal survival and the development of brain networks; however, it has been challenging to assess its role in the developing human brain. We employed serial quantitative magnetic resonance imaging to measure the rate of growth in circumscribed brain tissues from preterm to term age, and compared it with measures of electroencephalographic (EEG) activity during the first postnatal days by 2 different methods. EEG metrics of functional activity were computed: EEG signal peak-to-peak amplitude and the occurrence of developmentally important spontaneous activity transients (SATs). We found that an increased brain activity in the first postnatal days correlates with a faster growth of brain structures during subsequent months until term age. Total brain volume, and in particular subcortical gray matter volume, grew faster in babies with less cortical electrical quiescence and with more SAT events. The present findings are compatible with the idea that (1) early cortical network activity is important for brain growth, and that (2) objective measures may be devised to follow early human brain activity in a biologically reasoned way in future research as well as during intensive care treatment.

Cortical muscle control of spontaneous movements in human neonates

Anatomical studies show the existence of corticomotor neuronal projections to the spinal cord before birth, but whether the primary motor cortex drives muscle activity in neonatal 'spontaneous' movements is unclear. To investigate this issue, we calculated corticomuscular coherence (CMC) and Granger causality in human neonates. CMC is widely used as an index of functional connectivity between the primary motor cortex and limb muscles, and Granger causality is used across many fields of science to detect the direction of coherence. To calculate CMC and Granger causality, we used electroencephalography (EEG) to measure activity over the cortical region that governs leg muscles, and surface electromyography (EMG) over the right and left tibialis anterior muscles, in 15 healthy term and preterm neonates, during spontaneous movements without any external stimulation. We found that 17 leg muscles (10 right, seven left) in 12 neonates showed significant CMC, whose magnitude significantly correlated with postnatal age only in the beta frequency band. Further analysis revealed Granger causal drive from EEG to EMG in 14 leg muscles. Our findings suggest that the primary motor cortex drives muscle activity when neonates move their limbs. Moreover, the positive correlation between CMC magnitude and postnatal age suggests that corticomuscular communication begins to develop during the neonatal stage. This process may facilitate sensory-motor integration and activity-dependent development.

Modulation of EEG spectral edge frequency during patterned pneumatic oral stimulation in preterm infants

BACKGROUND

Stimulation of the nervous system plays a central role in brain development and neurodevelopmental outcomes. Thalamocortical and corticocortical development is diminished in premature infants and correlated to electroencephalography (EEG) progression. The purpose of this study was to determine the effects of orocutaneous stimulation on the modulation of spectral edge frequency fc = 90% (SEF-90), which is derived from EEG recordings in preterm infants.

METHODS

A total of 22 preterm infants were randomized to experimental and control conditions. Pulsed orocutaneous stimulation was presented during gavage feedings begun at ~32 wk postmenstrual age. The SEF-90 was derived from two-channel EEG recordings.

RESULTS

Compared with the control condition, the pulsed orocutaneous stimulation produced a significant reorganization of SEF-90 in the left (P = 0.005) and right (P < 0.0001) hemispheres. Notably, the left and right hemispheres showed a reversal in the polarity of frequency shift, demonstrating hemispheric asymmetry in the frequency domain. Pulsed orocutaneous stimulation also produced a significant pattern of short-term cortical adaptation and a long-term neural adaptation manifested as a 0.5 Hz elevation in SEF-90 after repeated stimulation sessions.

CONCLUSION

This is the first study to demonstrate the modulating effects of a servo-controlled oral somatosensory input on the spectral features of EEG activity in preterm infants.

Quantification of fetal magnetoencephalographic activity in low-risk fetuses using burst duration and interburst interval

OBJECTIVE

To identify quantitative MEG indices of spontaneous brain activity for fetal neurological maturation in normal pregnancies and examine the effect of fetal state on these indices.

METHODS

Spontaneous MEG brain activity was examined in 22 low-risk fetal recordings with gestational age (GA) ranging from 30 to 37 weeks. As major quantitative characteristics of spontaneous activity, burst duration (BD) and interburst interval (IBI) were studied in correlation with GA and fetal state.

RESULTS

IBI showed a decrease with gestational age (-0.21 s/week, P=0.0031). This trend was only maintained in the quiet-sleep state. With respect to BD, no significant trends were detected with GA and state.

CONCLUSION

IBI can be quantified as a fetal brain maturational parameter. The decrease in IBI over gestation was similar to the trend reported in the preterm neonatal EEG studies. Quiet sleep could be the optimal state to study such MEG maturational indices.

SIGNIFICANCE

With further investigation, indices extracted from spontaneous fetal brain activity may serve as an early warning for fetal neurological distress.

In and ex utero maturation of premature infants electroencephalographic indices

OBJECTIVES

To assess the effect of extra uterine life on continuity and amplitude of premature infants' cerebral activity at different gestational age as compared to soon after birth.

METHODS

Stable infants less than 34weeks gestation were prospectively recruited and EEG was recorded bi-weekly. Interburst interval and different wavelength amplitudes were digitally measured during the most discontinuous and most continuous (periods with longest and shortest interburst intervals, respectively) parts of the tracings. Linear regression was used to assess conceptional age prediction of interburst interval and wavelength amplitudes. Significant regression results were compared to the group of babies recorded close to delivery (newborn group).

RESULTS

144 EEG tracings from 59 infants were analyzed. Interburst intervals were significantly predicted by conceptional age in the newborn group only (p⩽0.002). Delta and theta amplitudes were significantly predicted by conceptional age in the newborn group and most of the other conceptional age groups (p<0.004). No significant differences were detected between the different groups.

CONCLUSIONS

Our data reiterates the normal maturation of cerebral activity in the premature infant and support the concept of similar in and ex-utero maturation of cerebral activity in stable premature infants.

SIGNIFICANCE

The effect of ex-utero maturation on the brain of stable premature infant is not readily discernible when using specific neonatal EEG indices.

Functional brain maturation assessed during early life correlates with anatomical brain maturation at term-equivalent age in preterm infants

BACKGROUND

Amplitude-integrated electroencephalogram (aEEG) is a reliable monitoring tool for electrocortical activity with good predictive value in preterm infants. Magnetic resonance imaging (MRI) is a good neuroimaging tool to detect brain lesions and to evaluate brain maturation. We hypothesized that early aEEG measures, recorded over the first 3 d of life in very preterm infants, correlate with brain maturation and injury score assessed by conventional MRI at term-equivalent age.

METHODS

Thirty-nine infants born at a mean (range) gestational age (GA) of 29.5 (27.0-31.9) wk and birth weight 1,230 (680-2,020) g had continuous aEEG during the first postnatal 72-84 h. aEEG maturity scores and average maximum and minimum amplitudes were evaluated. Conventional brain MRI was performed at 41.2 (37.1-44.1) wk postmenstrual age (PMA) on a 3T GE system and scored qualitatively for injury and maturation.

RESULTS

The average aEEG total maturity score and its cycling subscore were positively and significantly associated with the total MRI maturation score after adjustment for GA, morphine sedation, and PMA at MRI examination. No association was found between the aEEG measures and the MRI injury scores.

CONCLUSION

Early aEEG maturity seems to relate to structural MRI brain maturation at term-equivalent age in preterm infants.

Multimodality evaluation of the pediatric brain: DTI and its competitors

The development of the human brain, from the fetal period until childhood, happens in a series of intertwined neurogenetical and histogenetical events that are influenced by environment. Neuronal proliferation and migration, cell aggregation, axonal ingrowth and outgrowth, dendritic arborisation, synaptic pruning and myelinisation contribute to the 'plasticity of the developing brain'. These events taken together contribute to the establishment of adult-like neuroarchitecture required for normal brain function. With the advances in technology today, mostly due to the development of non-invasive neuroimaging tools, it is possible to analyze these structural events not only in anatomical space but also longitudinally in time. In this review we have highlighted current 'state of the art' neuroimaging tools. Development of the new MRI acquisition sequences (DTI, CHARMED and phase imaging) provides valuable insight into the changes of the microstructural environment of the cortex and white matter. Development of MRI imaging tools dedicated for analysis of the acquired images (i) TBSS and ROI fiber tractography, (ii) new tissue segmentation techniques and (iii) morphometric analysis of the cortical mantle (cortical thickness and convolutions) allows the researchers to map the longitudinal changes in the macrostructure of the developing brain that go hand-in-hand with the acquisition of cognitive skills during childhood. Finally, the latest and the newest technologies, like connectom analysis and resting state fMRI connectivity analysis, today, for the first time provide the opportunity to study the developing brain through the prism of maturation of the systems and networks beyond individual anatomical areas. Combining these methods in the future and modeling the hierarchical organization of the brain might ultimately help to understand the mechanisms underlying complex brain structure function relationships of normal development and of developmental disorders.

Fetal cerebrovascular resistance and neonatal EEG predict 18-month neurodevelopmental outcome in infants with congenital heart disease

OBJECTIVES

The purpose of this study was to investigate early markers of risk for neurobehavioral compromise in survivors with congenital heart disease (CHD).

METHODS

Pregnant women in whom a fetal CHD had been diagnosed before 24 weeks' gestational age (GA) were enrolled in this prospective pilot study for serial Doppler ultrasound assessment of the fetal middle cerebral artery (MCA) and umbilical arteries. The cerebral-to-placental resistance ratio (CPR) and MCA pulsatility index (PI) Z-scores for GA were calculated. After birth, subjects underwent high-density (128-lead) electroencephalography (EEG), and beta frequency (12-24 Hz) band EEG power, a measure of local neural synchrony, was analyzed. Neurodevelopment was assessed at 18 months with the Bayley Scales of Infant Development (BSID)-III.

RESULTS

Thirteen subjects were enrolled: four with hypoplastic left heart syndrome (HLHS), four with transposition of the great arteries (TGA) and five with tetralogy of Fallot (TOF). Compared with subjects with normal CPR, those with CPR < 1 (n = 7) had lower mean BSID cognitive scores (91.4 ± 4.8 vs. 99.2 ± 3.8, P = 0.008). Fetal MCA-PI Z-score also correlated with BSID cognitive score (r = 0.589, P = 0.03) as did neonatal EEG left frontal polar (r = 0.58, P = 0.037) and left frontal (r = 0.77, P = 0.002) beta power. Furthermore, fetal Doppler measures were associated with EEG power: fetuses with CPR < 1 had lower left frontal polar (t = 2.36, P = 0.038) and left frontal (t = 2.85, P = 0.016) beta power as newborns than did fetuses with normal CPR, and fetal MCA-PI Z-score correlated with neonatal EEG left frontal polar (r = 0.596, P = 0.04) and left frontal (r = 0.598, P = 0.04) beta power.

CONCLUSION

In fetuses with HLHS, TGA and TOF, abnormal cerebrovascular resistance predicts decreased neonatal EEG left frontal beta power and lower 18-month cognitive development scores.

Brain injury in chronically ventilated preterm neonates: collateral damage related to ventilation strategy

Brain injury is a frequent comorbidity in chronically ventilated preterm infants. However, the molecular basis of the brain injury remains incompletely understood. This article discusses the subtle (diffuse) form of brain injury that has white matter and gray matter lesions without germinal matrix hemorrhage-intraventricular hemorrhage, posthemorrhagic hydrocephalus, or cystic periventricular leukomalacia. This article synthesizes data that suggest that diffuse lesions to white matter and gray matter are collateral damage related to ventilator strategy. Evidence is introduced from the 2 large-animal, physiologic models of evolving neonatal chronic lung disease that suggest that an epigenetic mechanism may underlie the collateral damage.

EEG, brain maturation, and the development of retinopathy of prematurity

OBJECTIVES

The factors that influence the central nervous system (CNS) development can affect either the retina or the brain cortex. Immaturity of the brain cortex reflects immaturity of the retina and vice versa. The immature retina is more vulnerable than the mature retina, and is therefore more likely to develop retinopathy of prematurity (ROP). The aim of this study was to compare electroencephalographic brain maturity with ROP severity.

METHODS

Twenty-one prematurely born infants were divided into two groups according to the severity of ROP. The first group included 12 infants with ROP stage 3 or more and the second group included nine infants with ROP stage 2 or less. We have proposed an index of CNS maturity (M) as a percentage of interburst interval elongation compared with the norm using video-electroencephalography (vEEG).

RESULTS

The median M value was 1.07 (range = 0.43-4.44) for infants with severe ROP and -0.1 (range = -1.0 to 1.45) for infants with mild or no ROP (p = 0.000948).

CONCLUSIONS

The study revealed that CNS maturation delay expressed as M value was higher among infants with severe ROP than among infants with mild or no ROP. EEG examination in prematurely born infants may prove to be a useful tool for predicting ROP development.

Topography of maturational changes in EEG burst spectral power of the preterm infant with a normal follow-up at 2 years of age

OBJECTIVE

To quantify the electroencephalography (EEG) burst frequency spectrum of preterm infants by automated analysis and to describe the topography of maturational change in spectral parameters.

METHODS

Eighteen preterm infants <32weeks gestation and normal neurological follow-up at 2years underwent weekly 4-h EEG recordings (10-20 system). The recordings (n=77) represent a large variability in postmenstrual age (PMA, 28-36weeks). We applied an automated burst detection algorithm and performed spectral analysis. The frequency spectrum was divided into δ1 (0.5-1Hz), δ2 (1-4Hz), θ (4-8Hz), α (8-13Hz) and β (13-30Hz) bands. Spectral parameters were evaluated as a function of PMA by regression analysis. Results were interpolated and topographically visualised.

RESULTS

The majority of spectral parameters show significant change with PMA. Highest correlation is found for δ and θ band. Absolute band powers decrease with increasing PMA, while relative α and β powers increase. Maturational change is largest in frontal and temporal region.

CONCLUSIONS

Topographic distribution of maturational changes in spectral parameters corresponds with studies showing ongoing gyration and postnatal white matter maturation in frontal and temporal lobes.

SIGNIFICANCE

Computer analysis of EEG may allow objective and reproducible analysis for long-term prognosis and/or stratification of clinical treatment.

Peak-to-peak amplitude in neonatal brain monitoring of premature infants

OBJECTIVE

To assess the strength of association between alternative measures of electroencephalographic (EEG) signal peak-to-peak amplitude (ppA) and postmenstrual age (PMA) among a cohort of extremely premature infants.

METHODS

177 Two-channel EEG recordings 3-6h long were collected from 26 infants born before 29weeks of gestation. The raw EEG was converted into four different continuous measures of ppA: amplitude-integrated EEG (aEEG), range-EEG (rEEG), Gotman and Gloor's half-wave decomposition (HWD), and root of mean squares (RMS). For each ppA-measure EEG indices including mean, median, and 5% margins; indices of spread (width, standard deviation, coefficient of variation), and asymmetry were calculated for each 1min epoch. The medians of each index for the entire recording were tested for association with PMA using linear mixed models.

RESULTS

The log-transformed values of aEEG and rEEG indices of spread were highly associated with PMA (fixed effects R(β)(2)=0.84-0.89).

CONCLUSIONS

Indices of spread by aEEG or rEEG can be used as indicators of neonatal brain maturation. However, rEEG produces the absolute values that most closely approximate the raw EEG amplitudes.

SIGNIFICANCE

The indices of spread and rEEG as a measure of ppA provide a basis for improvements in neonatal EEG monitoring.

Multi-channel amplitude-integrated EEG characteristics in preterm infants with a normal neurodevelopment at two years of corrected age

AIM

To analyze quantitatively multi-channel amplitude-integrated EEG (aEEG) characteristics and assess regional differences.

METHODS

We investigated 40 preterm infants (postmenstrual age, PMA: range 27-37 weeks) with normal follow-up at 24 months of age, at a median postnatal age of 8 days using 4-h EEG recordings according to the international 10-20 system reduced montage. Nine (3 transverse and 6 longitudinal) channels were selected and converted to aEEG registrations. For each aEEG registration, lower margin amplitude (LMA), upper margin amplitude (UMA) and bandwidth (UMA-LMA) were calculated.

RESULTS

In all channels PMA and LMA showed strong positive correlations. Below 32 weeks of PMA, LMA was ≤5μV. Linear regression analysis showed a maximum LMA difference between channels of approximately 2 and 1μV at 27 and 37 weeks of PMA, respectively. The lowest are LMA values in the occipital channel and the highest values are in centro-occipital channels. In the frontal, centro-temporal and centro-occipital channels, UMA and bandwidth changed with PMA. No differences in LMA, UMA and bandwidth were found between hemispheres. Skewness of LMA values strongly correlated with PMA, positive skewness indicating an immature brain (PMA≤32 weeks) and negative skewness a maturing (PMA>32 weeks) brain.

CONCLUSIONS

We detected symmetric increase of aEEG characteristics, indicating symmetric brain maturation of the left and right hemispheres. Our findings demonstrate the clinical potential of computer-assisted analyses of aEEG recordings in detecting maturational features which are not readily identified visually. This may provide an objective and reproducible method for assessing brain maturation and long-term prognosis.

Developmental profiles of infant EEG: overlap with transient cortical circuits

OBJECTIVE

To quantify spectral power in frequency specific bands and commonly observed types of bursting activities in the EEG during early human development.

METHODS

An extensive archive of EEG data from human infants from 35 to 52 weeks postmenstrual age obtained in a prior multi-center study was analyzed using power spectrum analyses and a high frequency burst detection algorithm.

RESULTS

Low frequency power increased with age; however, high frequency power decreased from 35 to 45 weeks. This unexpected decrease was largely attributable to a rapid decline in the number of high frequency bursts.

CONCLUSIONS

The decline in high frequency bursting activity overlaps with a developmental shift in GABA's actions on neurons from depolarizing to hyperpolarizing and the dissolution of the gap junction circuitry of the cortical subplate.

SIGNIFICANCE

We postulate that quantitative characterization of features of the EEG unique to early development provide indices for tracking changes in specific neurophysiologic mechanisms that are critical for normal development of brain function.

Maturational changes in automated EEG spectral power analysis in preterm infants

Our study aimed at automated power spectral analysis of the EEG in preterm infants to identify changes of spectral measures with maturation. Weekly (10-20 montage) 4-h EEG recordings were performed in 18 preterm infants with GA <32 wk and normal neurological follow-up at 2 y, resulting in 79 recordings studied from 27(+4) to 36(+3) wk of postmenstrual age (PMA, GA + postnatal age). Automated spectral analysis was performed on 4-h EEG recordings. The frequency spectrum was divided in delta 1 (0.5-1 Hz), delta 2 (1-4 Hz), theta (4-8 Hz), alpha (8-13 Hz), and beta (13-30 Hz) band. Absolute and relative power of each frequency band and spectral edge frequency were calculated. Maturational changes in spectral measures were observed most clearly in the centrotemporal channels. With advancing PMA, absolute powers of delta 1 to 2 and theta decreased. With advancing PMA, relative power of delta 1 decreased and relative powers of alpha and beta increased, respectively. In conclusion, with maturation, spectral analysis of the EEG showed a significant shift from the lower to the higher frequencies. Computer analysis of EEG will allow an objective and reproducible analysis for long-term prognosis and/or stratification of clinical treatment.

Maternal dexamethasone and EEG hyperactivity in preterm fetal sheep

Maternal treatment with synthetic corticosteroids such as dexamethasone (DEX)significantly reduces neonatal morbidity and mortality, but its effects on the fetal brain remain unclear. In this study we evaluated the effects of DEX on EEG activity in preterm fetal sheep. Ewes at 103 days gestation received two intramuscular injections of DEX (12 mg, n = 8) or saline vehicle (n = 7) 24 h apart. Fetal EEG activity was recorded from 6 h before until 120 h after the first injection (DEX-1). DEX-1 was associated with a marked transient rise in total EEG power, maximal at 12 h (P < 0.001), with a relative increase in delta and reduced theta, alpha and beta activity, resolving by 24 h. Continuous EEG records showed a shift to larger but less frequent transient waveforms (P < 0.001). Unexpectedly, evolving epileptiform activity, consistent with electrographic and clinical seizures, developed from 178 ± 44 min after DEX-1.Similar but smaller changes were seen after the second injection. Following the injections, total power returned to control values, but the proportion of alpha activity progressively increased vs. controls (P < 0.001), with reduced interburst interval duration and number (P < 0.001). No histological neural injury or microglial activation was seen. In summary, exposure to maternal dexamethasone was associated with dramatic, evolving low-frequency hyperactivity on fetal cortical EEG recordings, followed by sustained changes consistent with maturation of fetal sleep architecture. We postulate that these effects may contribute to improved neonatal outcomes.

Cortical development in the fetus and the newborn: advanced MR techniques

Brain function is tightly linked to the development of the cortex. Until recently, assessing the human cortical development and folding was not possible in vivo. It is magnetic resonance imaging and new post-processing image analysis tools that have improved the understanding of cortical development. The combination of conventional magnetic resonance imaging and diffusion tensor imaging has further allowed depiction of the relationship of changes in intracortical layering and cortical folding. Being able to follow these early developmental processes has elucidated changes in early brain development due to changed environmental conditions in fetal life such as twinning and fetal growth restriction and postnatal conditions such as prematurity. This review further illustrates new data on brain structural asymmetries linked to the emergence of early language functions.

Effects of prenatal protein malnutrition on the electrical cerebral activity during development

Early protein restriction during the prenatal period has significant repercussions on the ontogeny and development of the central nervous system. The present study investigates whether early prenatal protein malnutrition could alter the electrical cerebral activity of the progeny. We used Sprague-Dawley female rats of 200 g randomly divided into three groups: a control group that received a diet with 25% of the protein content (lactalbumin), the experimental group, that received a diet with 6% of the protein content and the rehabilitated group that initially received a diet with 6% of the protein content, then switched to a diet with 25% of the protein content after the weaning period (P20D) up to 60 days of life (P60D). Reduction of the protein content from 25% to 6% of lactalbumin in the diet of pregnant rats produces impairment in the electrical cerebral activity in the progeny at P20D and at P60D. The power spectral analysis for each one of the electroencephalograms revealed that prenatal protein malnutrition in rats produced a significant reduction of the alpha (8-13 Hz) and the beta bands (13-30 Hz) and a significant increase of the theta (4-8 Hz), and delta bands (1-4 Hz), at two different stages of life (P20D and P60D). Similar results were obtained for the rehabilitated group. These results indicate that early malnutrition in life affects the ontogeny of the electrical cerebral activity. This insult probably disrupts the establishment of cortical neural circuits during the critical period of brain development. The rehabilitation period did not revert the impairment in the electrical cerebral activity produced by malnutrition. We used one-way ANOVA analysis, followed by Tukey test (*p<0.001).

Effect of hypothermia on amplitude-integrated electroencephalogram in infants with asphyxia

OBJECTIVES

Amplitude-integrated electroencephalogram (aEEG) at <6 hours is the best single outcome predictor in term infants with perinatal asphyxia at normothermia. Hypothermia has been used to treat those infants and proved to improve their outcome. The objectives of this study were to compare the predictive value of aEEG at <6 hours on outcomes in normothermia- and hypothermia-treated infants and to investigate the best outcome predictor (time to normal trace or sleep-wake cycling [SWC]) in normothermia- and hypothermia-treated infants.

METHODS

Seventy-four infants were recruited by using the CoolCap entry criteria, and their outcomes were assessed by using the Bayley Scales of Infant Development II at 18 months. The aEEG was recorded for 72 hours. Patterns and voltages of aEEG backgrounds were assessed.

RESULTS

The positive predictive value of an abnormal aEEG pattern at the age of 3 to 6 hours was 84% for normothermia and 59% for hypothermia. Moderate abnormal voltage background at 3 to 6 hours of age did not predict outcome. The recovery time to normal background pattern was the best predictor of poor outcome (96.2% in hypothermia, 90.9% in normothermia). Never developing SWC always predicted poor outcome. Time to SWC was a better outcome predictor for infants who were treated with hypothermia (88.5%) than with normothermia (63.6%).

CONCLUSIONS

Early aEEG patterns can be used to predict outcome for infants treated with normothermia but not hypothermia. Infants with good outcome had normalized background pattern by 24 hours when treated with normothermia and by 48 hours when treated with hypothermia.

Technical standards for recording and interpretation of neonatal electroencephalogram in clinical practice

Neonatal electroencephalogram (EEG), though often perceived as being difficult to record and interpret, is relatively easy to study due to the immature nature of the brain, which expresses only a few well-defined set of patterns. The EEG interpreter needs to be aware of the maturational changes as well as the effect of pathological processes and medication on brain activity. It gives valuable information for the treatment and prognostication in encephalopathic neonates. In this group, serial EEGs or EEG monitoring often gives additional information regarding deterioration/improvement of the brain function or occurrence of seizures.

Imaging biomarkers of outcome in the developing preterm brain

The neurodevelopmental disabilities of those who were born prematurely have been well described, yet the underlying alterations in brain development that lead to these changes remain poorly understood. Processes that are vulnerable to injury in the developing brain include maturation of oligodendrocyte precursors and genetically programmed changes in cortical connectivity; recent data have indicated that diffuse injury of the white matter accompanied by neuronal and axonal disruption is common in prematurely born infants. Recent advances in MRI include diffusion tensor imaging and sophisticated image analysis tools, such as functional connectivity, voxel-based morphometry, and mathematical morphology-based cortical folding strategies. These advanced techniques have shown that white matter structure is dependent on gestational age and have started to provide important information about the dynamic interactions between development, injury, and functional recovery in the preterm brain. Identification of early biomarkers for outcome could enable physicians and scientists to develop targeted pharmacological and behavioural therapies to restore functional connectivity.

Desenvolvimento cerebral em recém-nascidos prematuros

OBJETIVO:Rever a literatura atual que aborda o crescimento e o desenvolvimento cerebral de crianças prematuras e as alterações cognitivas e motoras que podem decorrer da prematuridade. FONTES DE DADOS: Foram utilizadas as bases de dados Medline e Lilacs, selecionados artigos publicados entre os anos de 2000 e 2007 e livros-texto com conteúdo relevante. SÍNTESE DOS DADOS: A evolução do recém-nascido pré-termo diferencia-se da evolução apresentada pela população a termo. Estudos têm demonstrado que ex-prematuros apresentam alterações anatômicas cerebrais que se associam a prejuízos cognitivos. Várias regiões do sistema nervoso central (substância cinzenta, substância branca, corpo caloso, núcleo caudado, hipocampo e cerebelo) têm seus volumes avaliados por neuroimagem e, apesar de resultados controversos, parecem ter desenvolvimento alterado nessa população. Diante disso, espera-se haver repercussão funcional e/ou cognitiva em crianças, adolescentes e adultos nascidos prematuramente. Ex-prematuros avaliados na infância tardia e na adolescência demonstram alterações de quociente de inteligência, memória, capacidade para cálculos e função cognitiva global. Déficits motores, na capacidade de planejamento e de associação, na coordenação motora e na atenção também foram relatados na literatura. CONCLUSÕES: A prematuridade pode levar a alterações anatômicas e estruturais do cérebro devido à interrupção das etapas de desenvolvimento pré-natal. Tais alterações podem causar déficits funcionais, tornando os ex-prematuros sujeitos a problemas cognitivos e motores, assim como suas repercussões nas atividades de vida diária, mesmo na adolescência e idade adulta.

Development of amplitude-integrated electroencephalography and interburst interval in the rat

Continuous monitoring of electrocortical brain activity with amplitude-integrated electroencephalography (aEEG) is important in neonatology. aEEG is affected by, for example, maturity, encephalopathy, and drugs. Neonatal research uses rat pups of different ages. Postnatal day (P) 7 rats are suggested to be equivalent neurodevelopmentally to near-term infants. We hypothesized that electroencephalography (EEG) and aEEG in P1-P21 rats follow the same developmental pattern with respect to background activity and the longest interburst interval (IBI) as that seen in infants from 23-wk gestational age (GA) to post-term. We examined aEEG and EEG on 49, unsedated rat pups with two clinical monitors. aEEG traces were analyzed for lower and upper margin amplitude, bandwidth and the five longest IBI in each trace were measured from the raw EEG. The median longest IBI decreased linearly with age by 5.24 s/d on average. The lower border of the aEEG trace was <5 microV until P7 and rose exponentially reaching 10 microV by P12. This correlated strongly with the decrease in IBI; both reflect increased continuity of brain activity with postnatal age. Based on aEEG trace analysis, the rat aEEG pattern at P1 corresponds to human aEEG at 23-wk gestation; P7 corresponds to 30-32 wk and P10 to 40-42 wk.

Quantitative fiber tracking analysis of the optic radiation correlated with visual performance in premature newborns

BACKGROUND AND PURPOSE

Many prematurely born neonates have abnormalities of vision or visual processing. This study tests the hypothesis that a correlation exists between the microstructure of the optic radiation and visual performance in premature neonates.

MATERIALS AND METHODS

Diffusion tensor imaging (DTI) was performed on 36 premature neonates ranging in age from 29 to 41 weeks of gestational age (GA) at time of MR imaging. DTI fiber tracking methods were developed to delineate the optic radiations and segment the tract into anterior, middle, and posterior regions. Structural development and spatial heterogeneity in the delineated optic radiations were quantitatively assessed with diffusion tensor parameters including fractional anisotropy (FA), directionally averaged diffusivity (D(av)), parallel diffusivity (lambda(1)), and transverse diffusivity (lambda( perpendicular)). Visual maturity of the preterm neonates at the time of MR imaging was assessed with a visual fixation task. Regression analysis was used to examine the relationship between neonatal visual performance and the microstructure of the optic radiation.

RESULTS

Fractional anisotropy within the optic radiation was observed to increase with GA (P < .0001). D(av), parallel diffusivity, and transverse diffusivity within the optic radiation each decreased with GA (P < .0003, P < .02, and P < .0001, respectively). The anterior segment of the optic radiation exhibited higher FA and lower D(av), parallel diffusivity, and transverse diffusivity (P < .005 each) than within the middle and posterior segments. Optic radiation fractional anisotropy correlated significantly with scores from the visual fixation tracking assessment, independent of GA (P < .006).

CONCLUSIONS

This study detected a significant link between the tissue architecture of the optic radiation and visual function in premature neonates.