Why is Newborn Sleep so Different than Adult Sleep?

Have you ever noticed that newborn sleep is all over the place? And happens often? And varies in length? And for as much as they sleep, they can’t make it all the way through the night? And sometimes at night they’re awake longer than they are during the day?

But why is it like this? Why don’t we sleep like this? Conversely, why don’t they sleep like us?

The chaos that is Newborn Sleep

In short, their brains and their circadian rhythms aren’t fully developed at birth.

The Brain

According to Mark S Blumberg, Andrew J Gall, and William D Todd in The development of sleep-wake rhythms and the search for elemental circuits in the infant brain on PubMed, the gist of it is newborns have the circuit needed to move from being awake to falling asleep, but it isn’t matured. For newborns, this circuit is solely in the brainstem; for those older than ~4 months it involves the brainstem and the forebrain.

Want a little more than just the gist of it? 😃

We all (newborns included) have a “flip-flop” switch model of sleep-wake regulation. Newborns have this switch (the circuit mentioned above) solely in the brainstem. For those ~4 months old and older, this switch functions between the brainstem and the forebrain.

Think of this flip-flop switch model as a seesaw at the playground (remember those?). One side of the seesaw is “sleep” and the other side is “wake”. Each side of the seesaw stops the other when it’s on. (You can’t be asleep and awake at the same time.) To tip the seesaw, or flip the switch, one side becomes slightly stronger than the other through homeostatic and circadian processes. Once it starts to tip towards that side, the other, weaker side’s inhibition increases, further tipping the seesaw. (2)

Homeostatic and circadian processes, as defined by Dr. Jasvinder Chawla, MD, MBA of Medscape, are: ”The homeostatic process is the drive to sleep that is influenced by the duration of wakefulness. [wake windows] The circadian process transmits stimulatory signals to arousal networks to promote wakefulness in opposition to the homeostatic drive to sleep.” (Italicized words are my own)

As your newborn grows, the two-way street between the brainstem and the forebrain is strengthened, contributing to more consolidated sleep (yay longer naps and stretches of sleep at night) and time awake (longer wake windows), matured sleep homeostatic processes, and the arrival of day and night circadian rhythms. (3)

These processes in babies are the foundation for the same processes in adults.

So cool, right?!

But, it's good to know that though these processes usually mature ~4 months old, every baby develops at different rates. It's common (and ok) for babies to not sleep through the night until ~1 year old. And, even once they are sleeping all night, it's not until ~5 years old that their "sleep architecture", or the length spent in each stage of sleep, mirrors that of an adult. (6)

Circadian Rhythms

The Sleep Foundation’s definition of the circadian rhythms is “Circadian Rhythms are 24-hour cycles that are part of the body’s internal clock, running in the background to carry out essential functions and processes. One of the most important and well-known circadian rhythms is the sleep-wake cycle.” So, there are a few circadian rhythms, but we’ll be focusing on the sleep-wake cycle.

It can take up to 12 weeks for Baby’s circadian rhythms to align fully with the 24-hour day. This is why it’s common for newborns to have night and day confusion in the early days. But, studies show that those rhythms start to align within the first few days after birth and having Baby join in on Mom’s daily activities helps with that alignment.(1)

The circadian rhythms are greatly influenced by light and in utero there is nearly zero light (the times you shine your flashlight on your belly isn’t enough to help with the set of the circadian rhythms). Plus, when Mom’s in the light during the day, she’s moving around more and essentially rocking the baby in her womb to sleep and she likely notices Baby’s movement far more at night because the rocking stopped.

No wonder they’re born confused.

Sleep Pattern Differences

Why so much time in REM, Baby?

One thought on why newborns spend the majority of their time asleep in the REM/active sleep stage versus the NREM/quiet sleep stage is for their safety. In quiet sleep, the breathing slows, the body settles, and it’s harder to wake from (which is dangerous if Baby isn’t getting enough oxygen).(1) Having the sleep cycles shorter may, too, be a safety mechanism.

What’s muscle atonia during REM sleep?

Muscle atonia is a weakening of the muscles and occurs during REM sleep in older babies up to adulthood. If it didn’t happen (and there is a very rare sleep disorder that interferes with the occurrence of it, REM sleep without atonia (RSWA)), we’d be acting out our dreams.

Yikes.

Since newborns don’t get muscle atonia, they act out their dreams. But they aren’t dreaming like we do, they’re more practicing working their muscles. Because of this, they’re very restless and noisy sleepers and love to fake us out in thinking they’re waking up when in reality they’re still sleeping or moving through a “transitional phase” of sleep.(1)

In conclusion

It’s fascinating what our bodies are capable of, even fresh out of the womb! Those early days can be so hard on sleep (among other things), but I hope having just a glimpse of the “why” behind the chaos brings a little peace in the present and hope for the future (because your baby is growing and will be able to sleep longer and more consistently soon!)!