Ontogeny of EEG sleep from neonatal through infancy periods

Sleep State Modulates Resting-State Functional Connectivity in Neonates

The spontaneous cerebral activity that gives rise to resting-state networks (RSNs) has been extensively studied in infants in recent years. However, the influence of sleep state on the presence of observable RSNs has yet to be formally investigated in the infant population, despite evidence that sleep modulates resting-state functional connectivity in adults. This effect could be extremely important, as most infant neuroimaging studies rely on the neonate to remain asleep throughout data acquisition. In this study, we combine functional near-infrared spectroscopy with electroencephalography to simultaneously monitor sleep state and investigate RSNs in a cohort of healthy term born neonates. During active sleep (AS) and quiet sleep (QS) our newborn neonates show functional connectivity patterns spatially consistent with previously reported RSN structures. Our three independent functional connectivity analyses revealed stronger interhemispheric connectivity during AS than during QS. In turn, within hemisphere short-range functional connectivity seems to be enhanced during QS. These findings underline the importance of sleep state monitoring in the investigation of RSNs.

Sleep-disordered breathing is common among term and near term infants in the NICU

OBJECTIVE

Among older infants and children, sleep-disordered breathing (SDB) has negative neurocognitive consequences. We evaluated the frequency and potential impact of SDB among newborns who require intensive care.

STUDY DESIGN

Term and near-term newborns at risk for seizures underwent 12-h attended polysomnography in the neonatal intensive care unit (NICU). Bayley Scales of Infant Development, third edition (Bayley-III) were administered at 18-22 months.

RESULT

The 48 newborns (EGA 39.3 ± 1.6) had a median pediatric apnea-hypopnea index (AHI) of 10.1 (3.3-18.5) and most events were central (vs obstructive). Maternal and prenatal factors were not associated with AHI. Moreover, neonatal PSG results were not associated with Bayley-III scores (P > 0.05).

CONCLUSION

SDB is common among term and near-term newborns at risk for seizures. Follow-up at ages when more nuanced testing can be performed may be necessary to establish whether neonatal SDB is associated with long-term neurodevelopmental disability.

Impact of brain injury on functional measures of amplitude-integrated EEG at term equivalent age in premature infants

OBJECTIVE

To evaluate the association between qualitative and quantitative amplitude-integrated EEG (aEEG) measures at term equivalent age (TEA) and brain injury on magnetic resonance imaging (MRI) in preterm infants.

STUDY DESIGN

A cohort of premature infants born at <30 weeks of gestation and with moderate-to-severe MRI injury on a TEA MRI scan was identified. A contemporaneous group of gestational age-matched control infants also born at <30 weeks of gestation with none/mild injury on MRI was also recruited. Quantitative aEEG measures, including maximum and minimum amplitudes, bandwidth span and spectral edge frequency (SEF₉₀), were calculated using an offline software package. The aEEG recordings were qualitatively scored using the Burdjalov system. MRI scans, performed on the same day as aEEG, occurred at a mean postmenstrual age of 38.0 (range 37 to 42) weeks and were scored for abnormality in a blinded manner using an established MRI scoring system.

RESULTS

Twenty-eight (46.7%) infants had a normal MRI or mild brain abnormality, while 32 (53.3%) infants had moderate-to-severe brain abnormality. Univariate regression analysis demonstrated an association between severity of brain abnormality and quantitative measures of left and right SEF₉₀ and bandwidth span (β=-0.38, -0.40 and 0.30, respectively) and qualitative measures of cyclicity, continuity and total Burdjalov score (β=-0.10, -0.14 and -0.12, respectively). After correcting for confounding variables, the relationship between MRI abnormality score and aEEG measures of SEF₉₀, bandwidth span and Burdjalov score remained significant.

CONCLUSION

Brain abnormalities on MRI at TEA in premature infants are associated with abnormalities on term aEEG measures, suggesting that anatomical brain injury may contribute to delay in functional brain maturation as assessed using aEEG.

The Visual Scoring of Sleep in Infants 0 to 2 Months of Age

In March 2014, the American Academy of Sleep Medicine (AASM) Board of Directors requested the Scoring Manual Editorial Board develop rules, terminology, and technical specifications for scoring sleep/wake states in full-term infants from birth to 2 mo of age, cognizant of the 1971 Anders, Emde, and Parmelee Manual for Scoring Sleep in Newborns. On July 1, 2015, the AASM published rules for scoring sleep in infants, ages 0-2 mo. This evidence-based review summarizes the background information provided to the Scoring Manual Editorial Board to write these rules. The Anders Manual only provided criteria for coding physiological and behavioral state characteristics in polysomnograms (PSG) of infants, leaving specific sleep scoring criteria to the individual investigator. Other infant scoring criteria have been published, none widely accepted or used. The AASM Scoring Manual infant scoring criteria incorporate modern concepts, digital PSG recording techniques, practicalities, and compromises. Important tenets are: (1) sleep/wake should be scored in 30-sec epochs as either wakefulness (W), rapid eye movement, REM (R), nonrapid eye movement, NREM (N) and transitional (T) sleep; (2) an electroencephalographic (EEG) montage that permits adequate display of young infant EEG is: F3-M2, F4-M1, C3-M2, C4-M1, O1-M2, O2-M1; additionally, recording C3-Cz, Cz-C4 help detect early and asynchronous sleep spindles; (3) sleep onsets are more often R sleep until 2-3 mo postterm; (4) drowsiness is best characterized by visual observation (supplemented by later video review); (5) wide open eyes is the most crucial determinant of W; (6) regularity (or irregularity) of respiration is the single most useful PSG characteristic for scoring sleep stages at this age; (7) trace alternant (TA) is the only relatively distinctive EEG pattern, characteristic of N sleep, and usually disappears by 1 mo postterm replaced by high voltage slow (HVS); (8) sleep spindles first appear 44-48 w conceptional age (CA) and when present prompt scoring N; (9) score EEG activity in an epoch as "continuous" or "discontinuous" for inter-scorer reliability; (10) score R if four or more of the following conditions are present, including irregular respiration and rapid eye movement(s): (a) low chin EMG (for the majority of the epoch); (b) eyes closed with at least one rapid eye movement (concurrent with low chin tone); (c) irregular respiration; (d) mouthing, sucking, twitches, or brief head movements; and (e) EEG exhibits a continuous pattern without sleep spindles; (11) because rapid eye movements may not be seen on every page, epochs following an epoch of definite R in the absence of rapid eye movements may be scored if the EEG is continuous without TA or sleep spindles, chin muscle tone low for the majority of the epoch; and there is no intervening arousal; (12) Score N if four or more of the following conditions are present, including regular respiration, for the majority of the epoch: (a) eyes are closed with no eye movements; (b) chin EMG tone present; (c) regular respiration; and (d) EEG patterns of either TA, HVS, or sleep spindles are present; and (13) score T sleep if an epoch contains two or more discordant PSG state characteristics (either three NREM and two REM characteristics or two NREM and three REM characteristics). These criteria for ages 0-2 mo represent far more than baby steps. Like all the other AASM Manual rules and specifications none are fixed in stone, all open for debate, discussion and revision with the fundamental goal to provide standards for comparison of methods and results.

COMMENTARY

A commentary on this article appears in this issue on page 291.

Rapid developmental emergence of stable depolarization during wakefulness by inhibitory balancing of cortical network excitability

The ability to generate behaviorally appropriate cortical network states is central to sensory perception and plasticity, but little is known about the timing and mechanisms of their development. I paired intracellular and extracellular recordings in the visual cortex of awake infant rats to determine the synaptic and circuit mechanisms regulating the development of a key network state, the persistent and stable subthreshold membrane potential (Vm) depolarization associated with wakefulness/alertness in cortical networks, called the "desynchronized" or "activated" state. Current-clamp recordings reveal that the desynchronized state is absent during the first 2 postnatal weeks, despite behavioral wakefulness. During this period, Vm remains at the resting membrane potential >80% of the time, regardless of behavioral state. Vm dynamics during spontaneous or light-evoked activity were highly variable, contained long-duration supratheshold plateau potentials, and high spike probability, suggesting an unstable and hyperexcitable early cortical network. Voltage-clamp recordings reveal that effective feedforward inhibition is absent at these early ages despite the presence of feedback inhibition. Stable membrane depolarization during wakefulness finally emerges 1-2 d before eye opening and is statistically indistinguishable from that in adults within days. Reduced cortical excitability, fast feedforward inhibition, and the slow cortical oscillation appear simultaneously with stable depolarization, suggesting that an absence of inhibitory balance during early development prevents the expression of the active state and hence a normal wakeful state in early cortex. These observations identify feedforward inhibition as a potential key regulator of cortical network activity development.