Phase-Based Cortical Synchrony Is Affected by Prematurity

Inter-areal synchronization by phase–phase correlations (PPCs) of cortical oscillations mediates many higher neurocognitive functions, which are often affected by prematurity, a globally prominent neurodevelopmental risk factor. Here, we used electroencephalography to examine brain-wide cortical PPC networks at term-equivalent age, comparing human infants after early prematurity to a cohort of healthy controls. We found that prematurity affected these networks in a sleep state-specific manner, and the differences between groups were also frequency-selective, involving brain-wide connections. The strength of synchronization in these networks was predictive of clinical outcomes in the preterm infants. These findings show that prematurity affects PPC networks in a clinically significant manner, suggesting early functional biomarkers of later neurodevelopmental compromise that may be used in clinical or translational studies after early neonatal adversity.

Impact of In Utero Exposure to Antiepileptic Drugs on Neonatal Brain Function

In utero brain development underpins brain health across the lifespan but is vulnerable to physiological and pharmacological perturbation. Here, we show that antiepileptic medication during pregnancy impacts on cortical activity during neonatal sleep, a potent indicator of newborn brain health. These effects are evident in frequency-specific functional brain networks and carry prognostic information for later neurodevelopment. Notably, such effects differ between different antiepileptic drugs that suggest neurodevelopmental adversity from exposure to antiepileptic drugs and not maternal epilepsy per se. This work provides translatable bedside metrics of brain health that are sensitive to the effects of antiepileptic drugs on postnatal neurodevelopment and carry direct prognostic value.

Use of complex visual stimuli allows controlled recruitment of cortical networks in infants

OBJECTIVE

To characterize cortical networks activated by patterned visual stimuli in infants, and to evaluate their potential for assessment of visual processing and their associations with neurocognitive development.

METHODS

Three visual stimuli, orientation reversal (OR), global form (GF), and global motion (GM), were presented to cohort of five-month-old infants (N = 26). Eye tracker was used to guide the stimulation and to choose epochs for analysis. Visual responses were recorded with electroencephalography and analysed in source space using weighted phase lag index as the connectivity measure. The networks were quantified using several metrics that were compared between stimuli and correlated to cognitive outcomes.

RESULTS

Responses to OR/GF/GM stimuli were observed in nearly all (96/100/100%) recordings. All stimuli recruited cortical networks that were partly condition-specific in their characteristics. The more complex GF and GM conditions recruited wider global networks than OR. Additionally, strength of the GF network showed positive association with later cognitive performance.

CONCLUSIONS

Network analysis suggests that visual stimulation recruits large-scale cortical networks that extend far beyond the conventional visual streams and that differ between stimulation conditions.

SIGNIFICANCE

The method allows controlled recruitment of wide cortical networks, which holds promise for the early assessment of visual processing and its related higher-order cognitive processes.

Prenatal exposure to antiepileptic drugs and early processing of emotionally relevant sounds

INTRODUCTION

Prenatal exposure to antiepileptic drugs (AEDs) is associated with developmental compromises in verbal intelligence and social skills in childhood. Our aim was to evaluate whether a multifeature Mismatch Negativity (MMN) paradigm assessing semantic and emotional components of linguistic and emotional processing would be useful to detect possible alterations in early auditory processing of newborns with prenatal AED exposure.

MATERIAL AND METHODS

Data on AED exposure, pregnancy outcome, neuropsychological evaluation of the mothers, information on maternal epilepsy type, and a structured neurological examination of the newborn were collected prospectively. Blinded to AED exposure, we compared a cohort of 36 AED-exposed with 46 control newborns at the age of two weeks by measuring MMN with a multifeature paradigm with six linguistically relevant deviant sounds and three emotionally uttered sounds.

RESULTS

Frontal responses for the emotionally uttered stimulus Happy differed significantly in the exposed newborns compared with the control newborns. In addition, responses to sounds with or without emotional component differed in newborns exposed to multiple AEDs compared with control newborns or to newborns exposed to only one AED.

CONCLUSIONS

These preliminary findings suggest that prenatal AED exposure may alter early processing of emotionally and linguistically relevant sound information.

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.

Use of eye tracking improves the detection of evoked responses to complex visual stimuli during EEG in infants

OBJECTIVE

To improve the reliability of detecting EEG responses evoked by complex visual stimuli to the level required for clinical use by integrating an eye tracker to the EEG setup and optimizing the analysis protocol.

METHODS

Infants were presented with continuous orientation reversal (OR), global form (GF), and global motion (GM) stimuli. Eye tracking was used to control stimulus presentation and exclude epochs with disoriented gaze. The spectral responses were estimated from 13 postcentral EEG channels using a circular variant of Hotelling's T2 test statistic.

RESULTS

Among 39 healthy infants, statistically significant (p < 0.01) responses to OR/GF/GM stimuli were found from 92%/100%/95% recordings, respectively. The specificity test of the detection algorithm, using non-stimulated baseline EEG, did not yield any false-positive findings. Taken together, this yields 15% improvement on average in the detection performance compared to that in the current literature.

CONCLUSIONS

Changes to the test protocol and incorporation of the eye tracking information improves the detection of responses to complex visual stimuli in infants.

SIGNIFICANCE

This work presents a test protocol suitable for use in a clinical environment at a level of reliability that allows individual diagnostics.

Dynamic eye tracking based metrics for infant gaze patterns in the face-distractor competition paradigm

OBJECTIVE

To develop new standardized eye tracking based measures and metrics for infants' gaze dynamics in the face-distractor competition paradigm.

METHOD

Eye tracking data were collected from two samples of healthy 7-month-old (total n = 45), as well as one sample of 5-month-old infants (n = 22) in a paradigm with a picture of a face or a non-face pattern as a central stimulus, and a geometric shape as a lateral stimulus. The data were analyzed by using conventional measures of infants' initial disengagement from the central to the lateral stimulus (i.e., saccadic reaction time and probability) and, additionally, novel measures reflecting infants gaze dynamics after the initial disengagement (i.e., cumulative allocation of attention to the central vs. peripheral stimulus).

RESULTS

The results showed that the initial saccade away from the centrally presented stimulus is followed by a rapid re-engagement of attention with the central stimulus, leading to cumulative preference for the central stimulus over the lateral stimulus over time. This pattern tended to be stronger for salient facial expressions as compared to non-face patterns, was replicable across two independent samples of 7-month-old infants, and differentiated between 7 and 5 month-old infants.

CONCLUSION

The results suggest that eye tracking based assessments of infants' cumulative preference for faces over time can be readily parameterized and standardized, and may provide valuable techniques for future studies examining normative developmental changes in preference for social signals.

SIGNIFICANCE

Standardized measures of early developing face preferences may have potential to become surrogate biomarkers of neurocognitive and social development.

Early neurophysiology and MRI in predicting neurological outcome at 9-10 years after birth asphyxia

OBJECTIVE

To assess whether early somatosensory evoked potentials (SEP) predict long-term neurodevelopmental outcome in normothermic, full-term infants with mild to moderate neonatal encephalopathy (NE), and to compare their predictive value to already available amplitude integrated EEG (aEEG) and magnetic resonance imaging (MRI).

METHODS

Fifty-six infants with post-asphyxia NE were prospectively recruited, and their SEP, aEEG and MRI data were acquired during the first five days. Follow-up continued to 9-10 years for assessment of neuromotor and neurocognitive development. We analysed SEP latency (N1 component), normality of aEEG background pattern, as well as patterns of injury on the neonatal MRI. Neurological outcome measures at 9-10 years included conventional MRI, Movement-ABC and the WISC-III NL.

RESULTS

A SEP latency <50 ms during the first five days was associated with a normal neuromotor outcome (p < 0.03), and a prolonged day 3 latency was associated with lower childhood IQ (p = 0.02). The presence of multiple seizures in aEEG, as well as a moderate or severe injury on the neonatal MRI was associated with a poor neuromotor score (p = 0.03 and p < 0.01, respectively). Combination of multiple techniques improved prediction of long-term outcome compared to single modality.

CONCLUSION

Early SEPs provide information that is comparable to the already available aEEG and MRI paradigms in the prediction of long-term outcome of full-term infants with mild to moderate neonatal encephalopathy.

SIGNIFICANCE

The present results call for further studies using early SEP to aid early assessment of infants treated with hypothermia.

Preterm EEG: a multimodal neurophysiological protocol

Since its introduction in early 1950s, electroencephalography (EEG) has been widely used in the neonatal intensive care units (NICU) for assessment and monitoring of brain function in preterm and term babies. Most common indications are the diagnosis of epileptic seizures, assessment of brain maturity, and recovery from hypoxic-ischemic events. EEG recording techniques and the understanding of neonatal EEG signals have dramatically improved, but these advances have been slow to penetrate through the clinical traditions. The aim of this presentation is to bring theory and practice of advanced EEG recording available for neonatal units.

In the theoretical part, we will present animations to illustrate how a preterm brain gives rise to spontaneous and evoked EEG activities, both of which are unique to this developmental phase, as well as crucial for a proper brain maturation. Recent animal work has shown that the structural brain development is clearly reflected in early EEG activity. Most important structures in this regard are the growing long range connections and the transient cortical structure, subplate. Sensory stimuli in a preterm baby will generate responses that are seen at a single trial level, and they have underpinnings in the subplate-cortex interaction. This brings neonatal EEG readily into a multimodal study, where EEG is not only recording cortical function, but it also tests subplate function via different sensory modalities. Finally, introduction of clinically suitable dense array EEG caps, as well as amplifiers capable of recording low frequencies, have disclosed multitude of brain activities that have as yet been overlooked.

In the practical part of this video, we show how a multimodal, dense array EEG study is performed in neonatal intensive care unit from a preterm baby in the incubator. The video demonstrates preparation of the baby and incubator, application of the EEG cap, and performance of the sensory stimulations.

Evaluation of an easy, standardized and clinically practical method (SurePrep) for the preparation of electrode-skin contact in neurophysiological recordings

The aim of this study was to assess the practicality, reliability and safety of a recently introduced method of skin preparation for EEG recordings. We compared the traditional skin abrasion (SA) method to a method called SurePrep (SP), which creates tiny incisions through the upper epithelial layers. The study comprised three parts. In part 1, forearm recordings (n = 400; ten healthy volunteers) were conducted to examine acute and late (24 h) impedances, skin reactions, as well as the effects on electrode movement artefacts. In part 2, the effect of repeated (up to nine) SP sticks on impedances was examined on the forearm skin in two subjects (n = 99). In part 3, preparation speed and skin impedances were measured from preparation of a standard EEG cap in four subjects (n = 74). Immediately after preparation, skin impedances were a little lower (n.s.) after SA, but the variability in impedances was significantly less after SP (p < 0.01). After one day, there was no mean impedance difference but a greater proportion of SP sites were >10 kOmega. The frequency of immediate skin irritations (93.5%) was much higher after SA compared to 42.5% after SP, but there was no clinically significant difference observed after one day. The SP method exposed interstitial fluid in 5% of cases, while SA caused a wound-like lesion in 4.5% of the sites. No macroscopic blood was observed in any case (n = 400). Three sticks with the SP device produced clinically sufficient (<10 kOmega) impedances in 85% of the cases, and a total of five to six sticks secured a sufficient skin contact in all skin sites examined (n = 99). Preparation of skin contacts in the EEG cap was faster by SP compared to SA in all four study subjects. Our results demonstrate that skin contacts of sufficient quality can be reliably, easily and quickly prepared by the SP method. SP is a useful alternative for EEG recordings in general, although SA may provide the slightly better preserved skin contacts needed for long-term recordings. Notably, SP could facilitate emergency care units, peripheral hospitals and after-hours EEG acquisition by people without special EEG training.