New technology reveals key role of sleep in infant brain development

Advanced technology now allows researchers to measure the sleep patterns of newborns, stimulating interest in studying how sleep affects brain development. Pediatric Research, The researchers investigated the role of sleep in prenatal and postnatal brain development.

study: Sleep promotes prenatal and postnatal brain development. Image credit: maxim ibragimov / Shutterstock.com

Infant Sleep Patterns

Healthy newborns sleep primarily during the first few days of life, with approximately 50% of this sleep being active sleep (AS). By the age of one month, total daily sleep time is 12-15 hours, with AS making up 50-80% of the infant’s sleep cycle.

Between 3 and 5 months of age, AS and quiet sleep (QS) are gradually replaced by rapid eye movement sleep (REM) and non-REM sleep, respectively. By 1 year of age, the proportion of AS gradually decreases to less than 50% and eventually transitions to QS.

These changes in sleep behavior can be observed in cortical activity measured by electroencephalography (EEG), and sleep patterns become more evident as infants age: for example, at 3–5 months of age, sleep spindles are observed during non-REM/citrate sleep, whereas at 5–8 months of age, delta bands of 0.5–4.0 Hz and sleep spindles of 7–14 Hz are observed during the non-REM sleep stage.

The role of sleep architecture in fetal and neonatal brain development

Rodent models have demonstrated that spontaneous activity associated with AS is essential for the development of cortical organization and thalamocortical connections.Similarly, spontaneous activity transients (SATs), which establish thalamocortical sensory pathways and intercortical connections, have been observed in human EEG from preterm infants between 24 and 33 weeks of gestation.

Both spontaneous and exogenous sensory inputs can trigger SAT. Spontaneous sensory input is first generated between 10-12 weeks postmenstrual and increases from 15-16 weeks postmenstrual. This sensory input manifests as twitches and has been shown to provide the sensory stimulation necessary for the development of the cortical body map in the somatosensory cortex.

In rats, by postnatal day 10, brain maturation is comparable to that of term newborns, SAT is observed during early sleep, and seizures become prominent during the first 2 weeks of life. These seizures originating from the red nucleus travel along neural pathways to the spinal cord, cerebellum, thalamus, and cortex to support somatosensory and motor development.

these In vivo Human studies have also confirmed that the quantity and quality of movement produced in the fetus, preterm, and term infants is associated with behavioral and neurodevelopmental outcomes. Additionally, higher SAT scores are often associated with larger brain volumes in preterm human infants.

How does sleep architecture change during early neurodevelopment?

The role of sleep adapts to changing developmental needs at different stages of life, and as a result, sleep architecture, including the amount and pattern of fetal seizures, also changes.

For example, between 33 and 34 weeks PMA, SATs are mainly observed during AS. Thereafter, the number of SATs increases during QS, which also increases to support efficient network formation.

Early neurodevelopment is also associated with different levels of gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter in the central nervous system (CNS). During this period, a “GABA shift” occurs, where activation of GABA receptors during early development leads to depolarization.

Neuronal excitation after the GABA shift is important for various prenatal neurodevelopmental processes, including spontaneous activity, synaptogenesis, and premyelination. GABA then switches to a hyperpolarizing effect, while the neurotransmitter promotes the inhibitory activity necessary to condition the fetal brain for specific postnatal requirements.

Sleep patterns are particularly important before the GABA shift, while waking activity and exogenous sensory stimulation become more important after the GABA shift. Therefore, preterm infants born before the GABA shift should not be exposed to excessive sensory stimulation during their waking hours, as these activities may interfere with ongoing neurodevelopmental processes and the development of important brain structures.

How does sleep affect newborn illnesses?

Preterm birth disrupts sleep patterns and impacts neurodevelopment: exposure to an immature nervous system and certain factors such as comorbidities alter sleep architecture, decreasing QS and increasing AS.

Additionally, neurological disorders such as hypoxic-ischemic encephalopathy worsen sleep-wake cycles, similarly leading to decreased QS and increased AS. Similarly, health conditions such as cerebral palsy increase asymmetry in sleep spindle activity and overall sleep disturbances.

Neurodiverse disorders such as autism spectrum disorder also contribute to sleep disorders, although the causal relationship is unclear. Respiratory conditions such as bronchopulmonary dysplasia may exacerbate sleep quality issues through obstructive sleep apnea, potentially affecting short- and long-term neurodevelopment.

Addressing these complex interactions is therefore crucial for developing effective early interventions for high-risk infants.

Current issues and future research

Improving sleep quality in preterm infants is critical for neurodevelopmental outcomes. However, it is unclear whether sleep directly influences development or reflects neurodevelopmental status. Therefore, randomized controlled trials are needed to evaluate the neuroprotective effects of improving sleep quality.

Advances in technology now allow for continuous and unobtrusive monitoring of sleep stages, but further research is needed to identify optimal methods for reliable and valid sleep assessment.

Defining “good quality sleep” requires balancing the neurobiological needs of the developing brain with environmental factors. It is therefore important to understand how sensory stimuli, from acoustic stimulation to music therapy, affect sleep. In both hospital and home settings, it is essential to tailor sleep hygiene interventions to the individual based on their developmental stage, underlying medical conditions, and family dynamics.