Rock-a-bye Baby

I started researching normal infant sleep after I had my daughter. Before giving birth I bought into sleep training culture and had planned to sleep train her fairly early. I attempted to sleep train her and hated it. It didn't fit for me and my kid.

The sleep books I read kept telling me my baby’s behavior was something that needed to be extinguished without explaining why the behavior existed in the first place. I never saw an explanation on why rocking a baby to sleep or carrying them during naps was harmful to their growth and development thereby justifying their need to be sleep trained.

The rationale I kept coming across for sleep training was this: babies need a lot of sleep and they sleep best when they sleep in the same environment instead of being transferred or helped to sleep. Plus, if you help them to sleep now you build dependence making sleep harder and worse for you and them down the road. 

But is this true? Is sleep training something you have to do or you're doomed? Or are these behaviors appropriate for their developmental stage?

What does the research say?

Biologically normal infant sleep looks and feels the way you'd expect it to when you learn babies are born with only 25% of their brain volume.

It's erratic, unpredictable and your feet may turn to dust from all the walking and bouncing you're doing. 

Below are the most common infant behaviors sleep trainers tell you to eliminate and the explanation for why those behaviors actually exist.

This isn't to say you shouldn't sleep train. It's totally an option, especially if it works for you and your kid.

This is to give perspective on WHY babies behave the way they do so you have a firm grasp on what's normal.

Learning what biologically normal newborn behavior is gave me perspective for why babies enjoy being held, rocked, and carried. It's taken away the pressure to have a perfect sleeper knowing she's just working out her evolutionary design. 

If you have a unicorn baby who sleeps alone without help (ya big jerk) this post is not for you. You can go away and don't tell any other parent you have such a perfect kid. Kidding. This is also for you because you'll probably want like 10 more kids since your first one is perfect and then you'll realize you just had a unicorn baby and are now stuck like the rest of us. Welcome. 

*I use the term infancy here as a catch all for any baby who is unable to speak or move independently. This typically stretches from birth - 1.5 years of life. 

Normal Newborn Behavior

1. Why do infants breastfeed to sleep? And why do they like to eat so frequently at night even when they no longer need it? 

Infants are the most immature mammals to be born. Why? Because they have big heads (!) and if they stayed in the womb any longer they would never make it out. As humans evolved and became bipedal our pelvic shape and diameter changed making it necessary for babies to be born earlier (infants really are accommodating). Because they are born earlier than other mammals and have immature respiratory, immune, digestive, and neurological systems they experience exterogestation, or gestating outside the womb. They are dependent on their caregiver to regulate their breathing, heart rate, temperature, emotions, etc. Scientists believe this "out of womb gestation" period ends when infants can crawl or walk. 

What does this have to do with breastfeeding? What constitutes normal and healthy infant sleep cannot be understood independent of nighttime breastfeeding as the two co-evolved and was designed by natural selection to maximize infant health and well-being. Frequent breastfeeding keeps babies in a lighter state of sleep making them less prone to deep sleep. 

But don't I want my baby to sleep deeply?! No, you actually don't.

Well, you might really want it, but it's not good for their survival. Since babies have immature respiratory and nervous systems if they sleep too deeply they don't arouse. Researchers think this may be one of the reasons SIDS is more prominent in western culture, but not in cultures where baby wearing and co-sleeping are the norm. Sleeping together (in same room or bed) promotes close contact with the mother, keeps babies in a lighter state of sleep and allows them to feed frequently. Which in the end keeps them healthy and alive.

Even when your baby weighs more than 15 pounds or is greater than 6 months old they still need help regulating their body and do so by frequent breastfeeding at night.  

2. Why does my baby calm down and fall asleep when held or rocked?

I’m sure you’ve noticed that when you rock or carry your baby their body relaxes and adopts a compact posture making them easier to hold. You might have also noticed that rocking your baby at a higher frequency helps them calm down quicker and relax into your body faster. 

Why does this happen?

You are witnessing remnants of a prehistoric brain. A recent study in Current Biology explored this topic by evaluating human infants and mouse pups. They found the calming response to fast movement (by being rocked or carried) may increase the survival probability of the infant in cases of emergency escape and work to support the mother-infant relationship.

If the baby is relaxed and calm when the mother is moving quickly they have the best chance of surviving whatever danger they’ve encountered. We might not be encountering any lions or tigers or bears (oh my!) nowadays, but that doesn't change the fact that our brains are hardwired to behave a certain way. 

Mammalian infants require constant care and attention for their physical and social survival and make sure to get it by keeping their mother close. Infants nervous, motor, and cardiac regulations are synced and regulated when carried by their caregiver; they are experiencing exterogestation (gestating outside the womb). The study found that holding, rocking, or carrying activated the Parasympathetic Nervous System (PNS) and lowered infants heart rate, reduced stress and helped them relax.

3. Why does my baby wake up when I put them down?

Infants can tell when the are put down because their Cerebellum, the little brain, helps them know where they are in space (known as proprioception) and alerts them to possible danger due to not being carried. The Cerebellum is responsible for our fight or flight reflex and is only "offline" when in REM sleep (the best time to transfer a baby if you're going to do it). Infants want to be carried so they can stay alive and they do this by staying close to their caregivers...they can't walk yet, dammit!

Next up: Bedsharing versus co-sleeping: the risks and benefits



Mother-baby Behavioral Sleep Laboratory at the University of Notre Dame. Research by Dr. James McKenna

Gianluca Esposito*, Sachine Yoshida*, Ryuko Ohnishi, Yousuke Tsuneoka, Maria del Carmen Rostagno, Susumu Yokota, Shota Okabe, Kazusaku Kamiya, Mikio Hoshino, Masaki Shimizu, Paola Venuti, Takefumi Kikusui, Tadafumi Kato and Kumi O. Kuroda. "Infant calming responses during maternal carrying in humans and mice". Current Biology, 2013.doi:10.1016/j.cub.2013.03.041

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