The Neuroscience of Being Human

The Neuroscience of Baby Sleep

Why the infant brain organises sleep so differently from the adult brain, what is actually happening during the hours the baby spends asleep, and why the fragmented sleep pattern that exhausts parents is the neurologically optimal pattern for the developing brain

The Neuroscience of Baby Sleep

882-word article with 8 Harvard references.

Key takeaways

  • The newborn brain spends approximately fifty per cent of its sleep time in REM (active) sleep, compared to approximately twenty per cent in the adult brain. The elevated REM proportion is not a design flaw. REM sleep is the state during which the brain processes and consolidates learning, strengthens new synaptic connections, and produces the spontaneous neural activity that drives the development of sensory circuits. The baby who sleeps for sixteen hours a day is spending approximately eight of those hours in a state of intense neural construction (Roffwarg et al., 1966).
  • The infant circadian system is not functional at birth. The suprachiasmatic nucleus, which serves as the brain's master clock, requires several weeks of exposure to light-dark cycles to calibrate, which is why newborns show no distinction between day and night. The circadian rhythm emerges gradually over the first three to four months, a timeline that is biologically determined and cannot be significantly accelerated.
  • Night waking in the first six months is neurologically normal and serves survival functions, including maintaining proximity to the caregiver, ensuring adequate feeding frequency, and preventing the deep, prolonged sleep states that are associated with increased SIDS risk in young infants.
  • The consolidation of sleep into longer nocturnal blocks, which typically begins between three and six months, coincides with the maturation of the circadian system and the development of the homeostatic sleep drive. The process is gradual, non-linear, and subject to disruption by developmental milestones, illness, and environmental changes.
  • Sleep training methods that involve leaving the infant to cry show behavioural changes in sleep patterns but do not necessarily reflect changes in sleep neurology. Studies measuring cortisol in sleep-trained infants have found that behavioural quieting can occur in the absence of physiological calming, raising questions about whether the infant is sleeping or has merely stopped signalling.

The brain that sleeps differently because it must

In 1966, Howard Roffwarg and colleagues published a paper that fundamentally changed our understanding of infant sleep. By mapping sleep stages across the lifespan, they demonstrated that the newborn brain spends approximately half of its total sleep time in REM sleep, a proportion that declines steadily through childhood to reach the adult level of approximately twenty per cent (Roffwarg et al., 1966). The finding raised an obvious question: why does the infant brain need so much REM sleep? The answer, which has been refined over subsequent decades of research, is that REM sleep is not a period of mental inactivity. It is a period of intense neural activity during which the brain is processing the day's sensory input, consolidating newly formed synaptic connections, and generating the spontaneous neural firing patterns that drive the maturation of sensory circuits.

The implication is striking. When the baby closes their eyes, the brain does not switch off. It shifts into a different mode of operation, one that is arguably more productive than wakefulness for certain types of neural development. The visual cortex is processing the day's visual input and refining the circuits that will support vision. The auditory cortex is consolidating the sound patterns that will eventually become language comprehension. The motor cortex is rehearsing the movement patterns that the baby practised while awake. The brain is, in a very real sense, doing homework, and the homework requires REM sleep as its medium.

Why night waking is not the enemy

The expectation that a baby should sleep through the night is culturally constructed, historically recent, and neurologically unrealistic for the first several months of life. Peter Fleming at the University of Bristol has argued that frequent night waking in young infants is a protective mechanism, maintained by evolution because the infant who wakes regularly maintains proximity to the caregiver, feeds frequently enough to support the metabolic demands of rapid growth, and avoids the prolonged deep sleep states that are associated with increased risk of sudden infant death syndrome (Fleming et al., 2015). The night waking is not a problem to be fixed. It is a feature of a system that is prioritising survival and development over parental convenience.

Invitation to reflect

If you are awake at three in the morning, holding a baby who has woken for the fourth time, the neuroscience offers you something that the sleep training industry may not: context. The baby is not waking because you have failed to teach them to sleep. The baby is waking because their brain is organised for frequent waking, because their circadian system is still calibrating, because their stomach is small and their metabolic needs are high, and because the evolutionary programme that governs infant sleep prioritises survival and neural development over consolidated nocturnal rest. This does not make the exhaustion easier. Nothing makes the exhaustion easier. But understanding that the pattern is neurologically normal, that the baby is not broken, and that the fragmented sleep is serving the developmental construction project that will produce a functional brain, may help you endure the exhaustion without the additional burden of believing you are doing something wrong. You are not doing something wrong. You are living through a neurobiological reality that every parent before you has lived through, and the baby's brain is doing exactly what it was designed to do. It is building itself, and the building happens, in large part, while the baby sleeps and you do not.

References

  1. Roffwarg, HP, Muzio, JN and Dement, WC (1966) Ontogenetic development of the human sleep-dream cycle. Science, 152(3722), pp. 604–619.
  2. Fleming, PJ, Blair, PS, Pease, A (2015) Sudden unexpected death in infancy: aetiology, pathophysiology, epidemiology and prevention in 2015. Archives of Disease in Childhood, 100(10), pp. 984–988.
  3. Middlemiss, W, Granger, DA, Goldberg, WA and Nathans, L (2012) Asynchrony of mother-infant hypothalamic-pituitary-adrenal axis activity following extinction of infant crying responses induced during the transition to sleep. Early Human Development, 88(4), pp. 227–232.
  4. Galland, BC, Taylor, BJ, Elder, DE and Herbison, P (2012) Normal sleep patterns in infants and children: a systematic review of observational studies. Sleep Medicine Reviews, 16(3), pp. 213–222.
  5. Henderson, JMT, France, KG, Owens, JL and Blampied, NM (2010) Sleeping through the night: the consolidation of self-regulated sleep across the first year of life. Pediatrics, 126(5), pp. e1081–e1087.
  6. Jenni, OG and Carskadon, MA (2007) Sleep behavior and sleep regulation from infancy through adolescence: normative aspects. Sleep Medicine Clinics, 2(3), pp. 321–329.
  7. Blumberg, MS, Gall, AJ and Todd, WD (2014) The development of sleep-wake rhythms and the search for elemental circuits in the infant brain. Behavioral Neuroscience, 128(3), pp. 250–263.
  8. Sadeh, A, Mindell, JA, Luedtke, K and Wiegand, B (2009) Sleep and sleep ecology in the first 3 years: a web-based study. Journal of Sleep Research, 18(1), pp. 60–73.

About the author

Gareth Strangemore-Jones, MHFA, DCST, PDPCP, HPD, DSFH, DMH, AHD, NCTJ, MSC-CPA, PGCE (FE) I & II

MNCPS (Reg.), MNCH (Reg.), MCNHC (Reg.), MAfSFH (Assoc.)

PSA (Acc.), FSE (Fellow), IFfS (Assoc.)

Mental Health First Aider, Pluralistic Counsellor, Clinical Psychotherapist. Consultant Medical Hypnotherapist, Mindfulness Teacher. PGCE-Trained Teacher, Lecturer, Corporate Trainer, Workplace Wellbeing Consultant. PR & Marketing Consultant, Psychology & Behaviour Advisor. Author, Journalist, Broadcaster. Advocate for Mental Health, People & Planet

Founder, CEO & Clinical Lead, The Brain Gym & Research Ltd. Gold standard human therapy, intelligently delivered