The Science of Sleep

Understand the why and the how behind your child’s sleep behaviours

When we know what goes on inside a child’s body whilst they are asleep (as well as the awake bits in between!), we can understand the sleep behaviours that we observe. Sleep science explains much of what we see going on on the outside, and whenever I share a scientific explanation for a sleep behaviour that’s been troubling a parent, it’s like seeing a lightbulb go off. Ding! Often this alone alleviates the stress that can come with the lack of understanding why your child is behaving in a certain way. The bonus is that it often helps solve the puzzle too.

So it’s really key to know firstly what normal sleep looks like and help set yourself up with realistic expectations. This also then informs you as to their developmental needs so you aren’t second guessing yourself the whole time, and as I’ve seen on too many occasions, feeling guilty that it’s your fault as a parent. It also means that when they change, whether over time or all of a sudden, you know how to change your sleep approach to match. Never is this more true than at around the age of 4 months, where sleep takes a monumental and permanent shift, and also takes parents by surprise. At least half (if not a great deal more) of parents that come to me for help with their child, the sleep issues stem from this change. SO it’s vital to  know what’s going on, and more importantly, what to do about it!

stages of sleep

Sleep is vital for their functioning, rest and development. During sleep, the body goes through many processes which facilitate towards a healthy, happy child, in both the brain and the body. The physiological responses and processes of our body are called circadian rhythms and follow a cycle which is around 24 hours. They are regulated within the brain by our ‘body clock’ located within the suprachiasmatic nucleus (SCN). The SCN is synchronised by sunlight in the morning via the optic nerve, and uses this to relay information to sub body clocks which influence the sleep/wake cycle, hormone release, body temperature, digestive system and immune function throughout a 24 hour period.

There are two types of sleep we all encounter throughout a good nights sleep; REM (Rapid Eye Movement) and non-REM sleep.

REM (light) sleep is important for brain functions and processes, which are essential for cognitive development, learning and functioning. While babies and young children sleep, their brains makes sense of what they have seen and learnt whilst awake. The brain processes and rehearses new information and new neural pathways are created in the process. Dreaming is a key function which increases the blood supply within the brain to optimise information retention. Children in this state are more mentally alert, their senses are sharpened and their cognitive ability is enhanced. This all leads to better information processing, and in turn promotes development.

Restoration is the primary focus of the body during non-REM (deep) sleep, which enables optimal gross development and health. Blood supply is increased to the developing muscles and growing tissues are repaired as the cells divide more quickly. Vital hormones are also released during sleep for growth and development. Health is improved from more sleep as during this state white blood cells are produced to build a better immune system. Non-REM sleep is broken down into 3 distinct phases from around the age of 4 months, which is one of the reasons why sleep can change quite dramatically after this time.

As each of these stages of sleep occur during distinct times overnight, so it is important for a baby or child to get a long and full nights sleep. Without spending those crucial hours in both REM and Non-REM sleep, your child’s brain will not have the opportunity to carry out those vital functions and processes for development and learning.

newborn sleep

The newborn phase is often referred to as the 4th trimester and for good reason. During these early months, babies continue life outside of the womb much as they did whilst inside the womb. They feed and sleep regularly and round the clock with no clear distinction. Inside the womb they have a pattern dependent on maternal movement, as a foetus’ body clock takes cues from maternal physiological changes such as activity and melatonin passing through the placenta. After birth, this hormonal connection is lost and it can take up to 12 weeks or longer for a baby to establish their own circadian rhythm. However, research shows that internal clocks can start to adjust within the first few days and newborns are receptive to environmental cues.

Although infants are not born with an internal cycle/regulated body clock, we can help nurture their regulation in number of ways. These include differentiating between night and day with noise and light level as well as engaging in daytime activity appropriate for your child’s age and developmental stage.

Newborns only cycle through 2 phases of sleep, REM and non-REM, with around 50% of their time spent snoozing in REM sleep. This is thought to be so that they can rouse easily for safety and protect them from SIDS. This increased time spent in light sleep means that newborns wake easily and frequently, and sleep in short bursts throughout the 24 hour day.

Although newborns average 16-18 hours of sleep in the first few weeks of life, there are huge variations in newborn sleep needs in babies under 6 months and some babies can sleep as little as 9 hours in a 24 hour period.

hormones and the sleep/wake cycle

Our circadian rhythms control our sleep/wake cycle by producing hormones and other vital substances in an intricate, fine-tuned pattern across a 24 hour period. This helps us fall asleep each night and wake each morning. A well timed body clock is crucial for a baby to start consolidating night sleep as they grow.

Melatonin is the sleep hormone that is key in regulating the body’s sleep/wake cycle.

Cortisol is the hormone that stimulates wakefulness.

Adenosine is a molecule that helps build ‘sleep pressure’.

Cortisol production occurs each morning as the body reaches this part of the cycle and is exposed to sunlight. Melatonin, the sleep hormone, is produced in abundance towards the end of the day as it gets darker and closer to bedtime.

beyond the 4th trimester

There is a major reorganisation of sleep at around 4 months which is often labelled as the 4 month sleep regression. This phase is actually a development of the brain, with maturing sleep stages and lengthening sleep cycles. So it doesn’t have to be feared, just addressed! It’s often when parents fail to realise their baby has changed, and so don’t know that they also need to adapt accordingly.

The amount of time spent in REM sleep falls to just 30%, and babies spend far more time in deep sleep. This non-REM sleep is now divided into 3 distinct sleep phases – N1, N2 and N3, much like ours as adults.

Sleep is no longer driven solely by a biological need to fall asleep, and your baby is now very conscious of how and where they fall asleep. This commonly leads to a resistance naps, with them often shortening, as well as the emergence of behavioural night wakings. Babies and children (as well as adults!) come close to waking, or actually awaken briefly, throughout the night as part of normal sleep patterns.

The large majority of deep sleep is taken in the first few hours, whereas most REM sleep occurs in the early hours and towards the end of the night. We are in a much lighter sleep and can be more easily roused.

sleep pressure

Understanding sleep pressure is crucial to understanding how long your baby can be awake before their next nap. It also determines when your baby is ready for bed based on their morning awake time

The role of adenosine in key in regulating the sleep/wake cycle, but it has many interactions with sleep that we need to consider. The homeostatic processes slow down with age, resulting in children being able to stay awake for longer periods and start to consolidate sleep. This is why newborns fall asleep quickly and often, and the need for naps reduces as children head towards pre-school age.

Sleep pressure is low during the day, reducing a baby’s ability to fall asleep easily, compared to night time. As it builds up towards bedtime, it works with the circadian rhythm to help a child fall asleep – this is always the easiest time to implement changes such as moving from feeding to putting down for sleep, or removing the dummy for example.

As sleep pressure reduces the more we sleep, the end of the night can be a tricky time to keep a baby asleep. It’s a common time for babies and children of all ages to struggle to stay asleep so head to the early rising blog if you’re struggling with this.

Is your baby or toddler wide awake baby before bedtime? Many parents report that their babies and toddlers get a ‘second wind’ before bedtime. Although sleep pressure builds up during the day, the circadian alerting system is working extra hard before bedtime to keep us awake (yes the same happens with us adults too!) by counteracting the homeostatic system. Resulting in a window otherwise known as the forbidden sleep zone. This is the worst time to try to get a child to sleep! So the best thing to do is just ride the energy, and get ready for the crash for bedtime!

My 5 top sleep questions that can be answered by sleep science

Can I spoil my baby? Absolutely not! Newborns often need cuddles and closeness for sleep and while you can start healthy sleep habits during this time, attachment is key for better sleep. Behavioural sleep issues don’t start until at least 3 months of age.

Is my baby waking out of habit? If they are just few weeks old, the answer is a definite no. However if your child is nearing or over the 4 month mark, and they are all of a sudden waking up more at night, they may have started to associate how and where they fall asleep with how they need to return back to sleep overnight.

Why is my baby napping more/less than others of the same age? Although the decrease of adenosine ‘sleep pressure’ is linear as they age, the speed at which is reduces is unique to each individual child. Therefore a child of a similar age may need longer/shorter wake windows before they are able to sleep, resulting in less/more frequent naps.

Why is my baby wide awake in the middle of the night? Night wakings are a complete normal part of sleep, and if your child isn’t distressed then leaving them to try to get themselves back to sleep on their own can help them learn what to expect from night time. If they are awake for long periods, there could be a lack of sleep pressure stopping them from sustaining a whole night of sleep.

When is the best time of day to implement sleep training for the first time? Bedtime is always the easiest time to start implementing a new way of falling asleep, because there’s so much helping your child fall asleep. It’s quicker, easier and less traumatic for all involved, plus it’s much more likely to be successful.

If you’re struggling with sleep and have more questions, I offer a free 15 minute assessment call so get in touch if you want to chat more about any issues you’re having, and find out if and how I can help.

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