Newborn infants learn during sleep

The emergence of consciousness: Science and ethics

The newborn human infant is conscious at a minimal level. It is aware of its body, itself and to some extent of the outside world. It recognizes faces and vowels to which it has been exposed. It expresses emotions like joy. Functional magnetic resonance imaging of the newborn brain shows highest activity in the somatosensory, auditory, and visual cortex but less activity in association area and the prefrontal cortex as compared with adults. There is an incomplete default mode network which is assumed to be related to consciousness. Although the fetus reacts to pain, maternal speaking, etc., it is probably not aware of this due to the low oxygen level and sedation. Assuming that consciousness is mainly localized in the cortex, consciousness cannot emerge before 24 gestational weeks when the thalamocortical connections from the sense organs are established. Thus the limit of legal abortion at 22-24 weeks in many countries makes sense. It should also be possible to withdraw or withhold life-saving therapy of extremely preterm infants, especially if they are severely brain-damaged. This may also apply to full-term infants with grade III hypoxic-ischemic encephalopathy, who show no signs of consciousness.

The maturation of cortical sleep rhythms and networks over early development

OBJECTIVE

Although neuronal activity drives all aspects of cortical development, how human brain rhythms spontaneously mature remains an active area of research. We sought to systematically evaluate the emergence of human brain rhythms and functional cortical networks over early development.

METHODS

We examined cortical rhythms and coupling patterns from birth through adolescence in a large cohort of healthy children (n=384) using scalp electroencephalogram (EEG) in the sleep state.

RESULTS

We found that the emergence of brain rhythms follows a stereotyped sequence over early development. In general, higher frequencies increase in prominence with striking regional specificity throughout development. The coordination of these rhythmic activities across brain regions follows a general pattern of maturation in which broadly distributed networks of low-frequency oscillations increase in density while networks of high frequency oscillations become sparser and more highly clustered.

CONCLUSION

Our results indicate that a predictable program directs the development of key rhythmic components and physiological brain networks over early development.

SIGNIFICANCE

This work expands our knowledge of normal cortical development. The stereotyped neurophysiological processes observed at the level of rhythms and networks may provide a scaffolding to support critical periods of cognitive growth. Furthermore, these conserved patterns could provide a sensitive biomarker for cortical health across development.

Electroencephalographic activity of preterm infants is increased by Family Nurture Intervention: a randomized controlled trial in the NICU

OBJECTIVE

To assess the impact of Family Nurture Intervention (FNI) on electroencephalogram (EEG) activity in preterm infants (26-34 weeks gestation).

METHODS

Two groups were tested in a single, level IV neonatal intensive care unit (NICU; standard care or standard care plus FNI) using a randomized controlled trial design. The intervention consists of sessions designed to achieve mutual calm and promote communication of affect between infants and their mothers throughout the NICU stay. EEG recordings were obtained from 134 infants during sleep at ∼35 and ∼40 weeks postmenstrual age (PMA). Regional brain activity (power) was computed for 10 frequency bands between 1 and 48 Hz in each of 125 electrodes.

RESULTS

Near to term age, compared to standard care infants, FNI infants showed robust increases in EEG power in the frontal polar region at frequencies 10 to 48 Hz (20% to 36% with p-values <0.0004). Effects were significant in both quiet and active sleep, regardless of gender, singleton-twin status, gestational age (26-30 or 30-35 weeks) or birth weight (<1500 or >1500 g).

CONCLUSION

FNI leads to increased frontal brain activity during sleep, which other investigators find predictive of better neurobehavioral outcomes.

SIGNIFICANCE

FNI may be a practicable means of improving outcomes in preterm infants.

Moderate acoustic changes can disrupt the sleep of very preterm infants in their incubators

AIM

To evaluate the impact of moderate noise on the sleep of very early preterm infants (VPI).

METHODS

Observational study of 26 VPI of 26-31 weeks' gestation, with prospective measurements of sound pressure level and concomitant video records. Sound peaks were identified and classified according to their signal-to-noise ratio (SNR) above background noise. Prechtl's arousal states during sound peaks were assessed by two observers blinded to the purpose of the study. Changes in sleep/arousal states following sound peaks were compared with spontaneous changes during randomly selected periods without sound peaks.

RESULTS

We identified 598 isolated sound peaks (5 ≤ SNR < 10 decibel slow response A (dBA), n = 518; 10 ≤ SNR < 15 dBA, n = 80) during sleep. Awakenings were observed during 33.8% (95% CI, 24-43.7%) of exposures to sound peaks of 5-10 dBA SNR and 39.7% (95% CI, 26-53.3%) of exposures to sound peaks of SNR 10-15 dBA, but only 11.7% (95% CI, 6.2-17.1%) of control periods. The proportions of awakenings following sound peaks were higher than the proportions of arousals during control periods (p < 0.005).

CONCLUSIONS

Moderate acoustic changes can disrupt the sleep of VPI, and efficient sound abatement measures are needed.

Computer-controlled stimulation for functional magnetic resonance imaging studies of the neonatal olfactory system

Aim Olfactory sensation is highly functional early in human neonatal life, with studies suggesting that odours can influence behaviour and infant–mother bonding. Due to its good spatial properties, blood oxygen level–dependent (BOLD) contrast functional magnetic resonance imaging (fMRI) has the potential to rapidly advance our understanding of the neural activity which underlies the development of olfactory perception in this key period. We aimed to design an ‘olfactometer’ specifically for use with neonatal subjects for fMRI studies of odour perception.

Methods We describe a fully automated and programmable, fMRI compatible system capable of presenting odorant liquids. To prevent contamination of the system and minimize between-subject infective risk, the majority of the olfactometer is constructed from single-use, readily available clinical equipment. The system was used to present the odour of infant formula milk in a validation group of seven neonatal subjects at term equivalent postmenstrual age (median age 40 weeks).

Results A safe, reliable and reproducible pattern of stimulation was delivered leading to well-localized positive BOLD functional responses in the piriform cortex, amygdala, thalamus, insular cortex and cerebellum.

Conclusions The described system is therefore suitable for detailed studies of the ontology of olfactory sensation and perception during early human brain development.

Neuropsychological development in children belonging to BECTS spectrum: long-term effect of epileptiform activity

Benign epilepsy with centrotemporal spikes (BECTS) is an idiopathic focal epileptic syndrome in childhood. It is called "benign" because the seizure and cognitive outcomes are usually favorable, but a significant number of children with BECTS present heterogeneous cognitive deficits correlated to NREM sleep epileptiform discharges. The atypical evolutions of BECTS form a spectrum of conditions suggesting that slow sleep nocturnal interictal epileptiform discharges (IEDs) specifically determine the neuropsychological deficit. Few follow-up studies of neuropsychological outcome in BECTS are available, and very often, slow sleep has not been recorded throughout night sleep. The present study analyzed the long-term effects of IEDs during NREM sleep on neuropsychological development in children with rolandic spikes. Thirty-three children with a diagnosis of BECTS were monitored for at least two years. Results show that these children are at higher risk for residual verbal difficulties, and the abnormal neuropsychological development is significantly correlated with a greater frequency of NREM sleep discharges, school-age epilepsy onset, and a higher number of antiepileptic drugs (AEDs). The findings are discussed in terms of how slow sleep IEDs affect the consolidation of verbal skills during critical epochs of neuropsychological development.

Neurobiology of secure infant attachment and attachment despite adversity: a mouse model

Attachment to an abusive caregiver has wide phylogenetic representation, suggesting that animal models are useful in understanding the neural basis underlying this phenomenon and subsequent behavioral outcomes. We previously developed a rat model, in which we use classical conditioning to parallel learning processes evoked during secure attachment (odor-stroke, with stroke mimicking tactile stimulation from the caregiver) or attachment despite adversity (odor-shock, with shock mimicking maltreatment). Here we extend this model to mice. We conditioned infant mice (postnatal day (PN) 7-9 or 13-14) with presentations of peppermint odor and either stroking or shock. We used (14) C 2-deoxyglucose (2-DG) to assess olfactory bulb and amygdala metabolic changes following learning. PN7-9 mice learned to prefer an odor following either odor-stroke or shock conditioning, whereas odor-shock conditioning at PN13-14 resulted in aversion/fear learning. 2-DG data indicated enhanced bulbar activity in PN7-9 preference learning, whereas significant amygdala activity was present following aversion learning at PN13-14. Overall, the mouse results parallel behavioral and neural results in the rat model of attachment, and provide the foundation for the use of transgenic and knockout models to assess the impact of both genetic (biological vulnerabilities) and environmental factors (abusive) on attachment-related behaviors and behavioral development.

Primary healthcare costs associated with sleep problems up to age 7 years: Australian population-based study

OBJECTIVES

In Australian 0-7-year olds with and without sleep problems, to compare (1) type and costs to government of non-hospital healthcare services and prescription medication in each year of age and (2) the cumulative costs according to persistence of the sleep problem.

DESIGN

Cross-sectional and longitudinal data from a longitudinal population study.

SETTING

Data from two cohorts participating in the first two waves of the nationally representative Longitudinal Study of Australian Children.

PARTICIPANTS

Baby cohort at ages 0-1 and 2-3 (n=5107, 4606) and Kindergarten cohort at ages 4-5 and 6-7 (n=4983, 4460).

MEASUREMENTS

Federal Government expenditure on healthcare attendances and prescription medication from birth to 8 years, calculated via linkage to Australian Medicare data, were compared according to parent report of child sleep problems at each of the surveys.

RESULTS

At both waves and in both cohorts, over 92% of children had both sleep and Medicare data. The average additional healthcare costs for children with sleep problems ranged from $141 (age 5) to $43 (age 7), falling to $98 (age 5) to $18 (age 7) per child per annum once family socioeconomic position, child gender, global health and special healthcare needs were taken into account. This equates to an estimated additional $27.5 million (95% CI $9.2 to $46.8 million) cost to the Australian federal government every year for all children aged between 0 and 7 years. In both cohorts, costs were higher for persistent than transient sleep problems.

CONCLUSIONS

Higher healthcare costs were sustained by infants and children with sleep problems. This supports ongoing economic evaluations of early prevention and intervention services for sleep problems considering impacts not only on the child and family but also on the healthcare system.

A review of embodiment in autism spectrum disorders

In classical approaches to cognition, sensory, motor, and emotional experiences are stripped of domain-specific perceptual and sensorimotor information, and represented in a relatively abstract form. In contrast, the embodied cognition framework suggests that our representations retain the initial imprint of the manner in which information was acquired. In this paper, we argue that individuals with autism spectrum disorders (ASD) display impairments in the temporal coordination of motor and conceptual information (as shown in gesture research) and striking deficits in the interpersonal mimicry of motor behaviors (as shown in yawning research) - findings we believe are consistent with an embodied account of ASD that includes, but goes beyond, social experiences and is driven in part by significant but subtle motor deficits. In this paper, we review the research examining an embodied cognition account of ASD, and discuss its implications.

Humans can learn new information during sleep

During sleep, humans can strengthen previously acquired memories, but whether they can acquire entirely new information remains unknown. The nonverbal nature of the olfactory sniff response, in which pleasant odors drive stronger sniffs and unpleasant odors drive weaker sniffs, allowed us to test learning in humans during sleep. Using partial-reinforcement trace conditioning, we paired pleasant and unpleasant odors with different tones during sleep and then measured the sniff response to tones alone during the same nights' sleep and during ensuing wake. We found that sleeping subjects learned novel associations between tones and odors such that they then sniffed in response to tones alone. Moreover, these newly learned tone-induced sniffs differed according to the odor pleasantness that was previously associated with the tone during sleep. This acquired behavior persisted throughout the night and into ensuing wake, without later awareness of the learning process. Thus, humans learned new information during sleep.

High density electroencephalography in sleep research: potential, problems, future perspective

High density EEG (hdEEG) during sleep combines the superior temporal resolution of EEG recordings with high spatial resolution. Thus, this method allows a topographical analysis of sleep EEG activity and thereby fosters the shift from a global view of sleep to a local one. HdEEG allowed to investigate sleep rhythms in terms of their characteristic behavior (e.g., the traveling of slow waves) and in terms of their relationship to cortical functioning (e.g., consciousness and cognitive abilities). Moreover, recent studies successfully demonstrated that hdEEG can be used to study brain functioning in neurological and neuro-developmental disorders, and to evaluate therapeutic approaches. This review highlights the potential, the problems, and future perspective of hdEEG in sleep research.

The predictive nature of individual differences in early associative learning and emerging social behavior

Across the first year of life, infants achieve remarkable success in their ability to interact in the social world. The hierarchical nature of circuit and skill development predicts that the emergence of social behaviors may depend upon an infant's early abilities to detect contingencies, particularly socially-relevant associations. Here, we examined whether individual differences in the rate of associative learning at one month of age is an enduring predictor of social, imitative, and discriminative behaviors measured across the human infant's first year. One-month learning rate was predictive of social behaviors at 5, 9, and 12 months of age as well as face-evoked discriminative neural activity at 9 months of age. Learning was not related to general cognitive abilities. These results underscore the importance of early contingency learning and suggest the presence of a basic mechanism underlying the ontogeny of social behaviors.

Neural language networks at birth

The ability to learn language is a human trait. In adults and children, brain imaging studies have shown that auditory language activates a bilateral frontotemporal network with a left hemispheric dominance. It is an open question whether these activations represent the complete neural basis for language present at birth. Here we demonstrate that in 2-d-old infants, the language-related neural substrate is fully active in both hemispheres with a preponderance in the right auditory cortex. Functional and structural connectivities within this neural network, however, are immature, with strong connectivities only between the two hemispheres, contrasting with the adult pattern of prevalent intrahemispheric connectivities. Thus, although the brain responds to spoken language already at birth, thereby providing a strong biological basis to acquire language, progressive maturation of intrahemispheric functional connectivity is yet to be established with language exposure as the brain develops.

One-month-old human infants learn about the social world while they sleep

Although infants display preferences for social stimuli early in their lives, we know relatively little about the mechanisms of infant learning about the social world. In the current set of studies, 1-month-old infants underwent an adapted eyeblink conditioning paradigm to examine learning to both 'social' and non-social cues. While infants were asleep, they were presented with either a 'social' stimulus (a female voice) or one of two non-social stimuli (tone or backward voice) followed by an airpuff presented to the eyelid. Infants in the experimental groups displayed increased learning across trials, regardless of stimulus type. However, infants conditioned to the 'social' stimulus showed increased learning compared to infants conditioned to either of the non-social stimuli. These results suggest a mechanism by which learning about the social world occurs early in life and the power of ecologically valid cues in facilitating that learning.

Unconscious knowledge: A survey

The concept of unconscious knowledge is fundamental for an understanding of human thought processes and mentation in general; however, the psychological community at large is not familiar with it. This paper offers a survey of the main psychological research currently being carried out into cognitive processes, and examines pathways that can be integrated into a discipline of unconscious knowledge. It shows that the field has already a defined history and discusses some of the features that all kinds of unconscious knowledge seem to share at a deeper level. With the aim of promoting further research, we discuss the main challenges which the postulation of unconscious cognition faces within the psychological community.

The newborn intensive care unit environment of care: how we got here, where we're headed, and why

The newborn intensive care unit (NICU) is a life-defining place for many infants, families, and caregivers. The place in which such events occur is often remembered for its sights, sounds, and smells, but the physical environment of the NICU is far more than a memory tag; it can directly influence the quality of the experience for all of its inhabitants. A growing body of evidence demonstrates the profound impact of the physical environment on growth and development of the neonatal brain. The value of skin-to-skin care is now established. Psychology, sociology, and occupational health provide additional insight into the effect of the NICU setting on families and caregivers. Together, these lines of evidence point to the need for individualized environments. Single-family rooms are a growing trend in the NICU because they allow for individualized environments. Careful planning can avoid pitfalls and bring benefit to babies, families, and caregivers alike.

Beyond dreams: do sleep-related movements contribute to brain development?

Conventional wisdom has long held that the twitches of sleeping infants and adults are by-products of a dreaming brain. With the discovery of active (or REM) sleep in the 1950s and the recognition soon thereafter that active sleep is characterized by inhibition of motor outflow, researchers elaborated on conventional wisdom and concluded that sleep-related twitches are epiphenomena that result from incomplete blockade of dream-related cortical activity. This view persists despite the fact that twitching is unaffected in infants and adults when the cortex is disconnected from the brainstem. In 1966, Roffwarg and colleagues introduced the ontogenetic hypothesis, which addressed the preponderance of active sleep in early infancy. This hypothesis posited that the brainstem mechanisms that produce active sleep provide direct ascending stimulation to the forebrain and descending stimulation to the musculature, thereby promoting brain and neuromuscular development. However, this hypothesis and the subsequent work that tested it did not directly address the developmental significance of twitching or sensory feedback as a contributor to activity-dependent development. Here I review recent findings that have inspired an elaboration of the ontogenetic hypothesis. Specifically, in addition to direct brainstem activation of cortex during active sleep, sensory feedback arising from limb twitches produces discrete and substantial activation of somatosensory cortex and, beyond that, of hippocampus. Delineating how twitching during active sleep contributes to the establishment, refinement, and maintenance of neural circuits may aid our understanding of the early developmental events that make sensorimotor integration possible. In addition, twitches may prove to be sensitive and powerful tools for assessing somatosensory function in humans across the lifespan as well as functional recovery in individuals with injuries or conditions that affect sensorimotor function.

Sleep and Infant Learning

Human neonates spend the majority of their time sleeping. Despite the limited waking hours available for environmental exploration, the first few months of life are a time of rapid learning about the environment. The organization of neonate sleep differs qualitatively from adult sleep, and the unique characteristics of neonatal sleep may promote learning. Sleep contributes to infant learning in multiple ways. First, sleep facilitates neural maturation, thereby preparing infants to process and explore the environment in increasingly sophisticated ways. Second, sleep plays a role in memory consolidation of material presented while the infant was awake. Finally, emerging evidence indicates that infants process sensory stimuli and learn about contingencies in their environment even while asleep. As infants make the transition from reflexive to cortically mediated control, learned responses to physiological challenges during sleep may be critical adaptations to promote infant survival.