Essential Research On Baby's Sleep


Getting your baby to sleep through the night turns out to be a universal human challenge. A baby sleeping is not just important for its parents' sanity, it's fundamental for the baby's development.

A newborn baby is spending 16 hours a day sleeping. That's an extraordinary amount of time to be asleep. There's a lot of mystery there about what's going on in these babies. Why are they sleeping so much?

The brain is absolutely on fire. It is very, very active during sleep. This is, in some sense, me-time for your brain. This is the time when your brain lives out its own existence, if you will. But you're unaware of it. Which is, for me, absolutely fascinating.

I feel like we are really just at the tip of the iceberg with sleep science. We feel better during the day, we think better during the day, because of something that's happened in the brain during sleep. I want to understand how does sleep make you better?

Andre Fenton, Director, Cognitive Neurobiology Lab, New York University, USA explains the research.

When I was a new parent, I told all my friends, "I totally got this. I know how to think about babies, this is gonna be really easy." Little did I know. There we were, new parents. And then all hell broke loose, and it was only because I couldn't figure out how to get my daughter to sleep through the night.

As a neuroscientist, it had not occurred to me to actually study sleep. But when I was a newborn parent, there's no knowledge about what is normal and what one should do. And so I decided to study sleep in infants. Surely, we could find out how to think about baby sleep in a scientifically grounded, biologically-based way.


Everyone knows that baby sleep seems erratic early on, and eventually it becomes regular. So we wanted to find out when do babies learn to sleep like we do? Does it develop gradually? Does it suddenly occur in the ninth month, for example? Or does everyone have their own rhythm?

The first thing to do was to figure out how to get the data. We discovered that there's a whole set of apps that people are using to log events about their babies. Most importantly, sleeping. That for us is a treasure trove.

So we talked to some app developers, and this collaboration between the app developers and the scientists became the NYU Baby Sleep Study.

We're going to visit some of the families who've signed up for the study and find out how it is that they're actually using this application, which will give us a sense of how the data are being collected.

The way we're used to collecting data is in a small number of subjects, but with absolutely precise and accurate measurements.

In this case, though, we have no control over anything. We're not even making any of the measurements. And so we don't know whether the times are accurate to the minute, or to the hour.

The thing that struck me the most when I got to meet some of the study participants is that they were accurate to the minute. It was clear that the error was, by assertion, no more than five minutes. To have minute-precise data, and to have millions of those data points, makes you extremely confident as a scientist in coming to conclusions.

Please meet my longtime colleague, Pascal Wallisch. Pascal has a long history of working with lots of data before they were called "big data."

What you're looking at here is a distribution of babies in the study around the world. So every dot here represents a baby. We have logged data from about 1,000 babies, and they have produced a total of six million events made up out of about 1.5 million sleep events, 2.5 million eating events, and 1.5 million diaper change events. Collectively.


If you have a large number of babies and they each have their own rhythm, but there's a common, underlying pattern to that rhythm, when you sample enough babies, the pattern will emerge. And we're beginning to answer the first simple question, when does the sleep pattern emerge?

The question that we're trying to answer is, "Will my baby sleep through the night?" That's really what they want to know, when that will happen.

We have started to analyze the data, and we see trends. But to be very clear, this is very early days. We are not comfortable to publish this yet.

But what you see here is that at one month, there's no clear pattern of when the baby's eating or sleeping. So, basically sleeping and eating at random, which is very taxing on the parents. This was in fact the problem.

But then, within about four months, an initial cycle is emerging. And by the time you get to eight months, there's a hint of a pattern. And then within a year, this clear pattern emerges.

Babies are sleeping through the night. They sleep soon after feeding in the morning, and about five hours later in the early afternoon, that's the third time in which they very reliably sleep.

If we had a big enough data set, this would be very simple to turn into a website where an individual person could come and say, "Oh, my kid is within the normal limits. Everything's fine." Or, "Everything is likely to be fine." Or, "My kid is outside of the normal limits."

That would be an early sign that you could recognize maybe there's a reason for concern, or some kind of intervention, or, at least, you know, close scrutiny.

The really amazing thing is to recognize that the transition from no sleep pattern to a sleep pattern is something that almost all babies do. And it'll take about a year.

Mark Bloomberg, Professor, Psychology dan Brain Science, University of Iowa, USA explains the research.

I've always been a terrible sleeper. And, you know, there's this old adage that we study the things that we're bad at.

I always wake up in a groggy state. I never use an alarm clock. Alarm clocks are terrible, you know, 'cause it's important to wake up naturally. Despite my knowing that, I still manage to get bad night's sleep after bad night's sleep. Woe is me.

All animals on this planet have a 24-hour cycle that is tightly linked to the sun. That's called a circadian rhythm. 

So for us humans, you're awake during the day, and asleep during the night in the brain, and it is regulated by the master clock located within a part of the brain called the hypothalamus. But that's not true for babies.


When I first started getting involved in sleep research, I started studying baby rats. What happens with babies, baby humans, baby rats, is that they cycle very rapidly between sleep and wake.

If you're looking at a baby like this, it's just complete relaxation... and then all of a sudden... Boom. Awake. And you can tell it's awake because the left arm and the left leg are in the air at the same time. And then, look at that, it just goes from this... vroom. Asleep.

So over the course of 24 hours, they can have hundreds of cycles between sleep and wake. And so that's what makes babies different. So we wanted to know, you know, why would that be?

So we started out with a very simple experiment. We put a dye into the brain of a newborn rat in the master clock region. And we wanted to know at what age does that part of the brain connect up with other parts of the brain that are important for sleep and wake?

When these baby rats were born, we have all of this red dye here where the master clock is... but when we look closer to the brain stem, we see nothing. We see no labeling at all. So, it's as if the wires connecting this part of the brain to this part of the brain just, just don't exist yet.

But, if we come over here to a week later, we now see all of this area now is red. It was black over here, it's now red over here, and that's an indication that this part of the brain is now talking to this part of the brain.

And what we found was it's also happening in humans.If you look at a model brain, I'm going to pull it apart to expose the brain stem, and the sleep/wake cycles are largely regulated in this region down here.

And then, up here in the hypothalamus, this is where the so-called master clock is located, and that's going to be governing your circadian rhythm. And in newborn infants these areas are not talking to each other, either directly or indirectly. What that means is that those connections are what's responsible for giving rise to the circadian rhythm.

Maybe if you're a parent and you're struggling to deal with the fact that you're sleep deprived because your baby is not, you know, getting through the night, you might just think, "Well, I just have to wait for these connections to form."

Because prior to three to four months, there's very little you can do to help babies sleeping throughout the night. It's just gonna have to wait for the for the circadian system to connect them.


When we studied these rats, I started noticing all of this twitching. I was using twitching as a sign that the animals were sleeping. 

But when you see a behavior like this, and it's remarkable behavior... In many animals it looks like a seizure... You start to wonder, what do these twitches represent?

This is my dog, Katie... and you can see the vigorous twitching in both of her limbs, and even some fluttering in the face. Most people look at this and they think that Katie is, you know, chasing rabbits in her sleep.

The historical view going back hundreds of years, if not millennia, is that twitching is just a byproduct of dreams. And so if you dream about running, your legs will kick a little bit. That was the dominant view, some people still believe it.

And there was this contrast between what I was seeing with my own two eyes and what I was reading in the scientific literature. So over time I just kept asking questions about it. And it evolved into a whole research program that I never anticipated.

So for these experiments, we're trying to do very precise measures of twitching, and we want to know, can we see evidence of brain activity that's related specifically to the movements that we're picking up during sleep?

What we found was when a baby is twitching, what's happening, similar to when you watch a submarine movie... when all the people on the submarine are being asked to be very, very quiet because they're about to do a sonar test.

That's similar to when these babies are asleep. There is very little brain activity... and then when a baby is twitching, boom. That is a sonar test. The captain of the submarine will shoot off one ping only out into the water. And that pinging creates an echo that is allowing you to see what's out there.

In the same way that the brain is kind of trying to figure out, "What's out there?" You know, "What do my limbs do? How many muscles do I have? How are they connected to one another?"

And what we think is happening with twitches is that you're mapping your body. You're learning about the muscles of your body, you're learning about how those muscles control joints, you learn about the relationships, the synergies among the different muscles in your limbs.

A single twitch can produce activity in hundreds, probably thousands, of neurons. And that's what we see in the EEG activity of these human infants. It is how the baby learns what kind of body that it has.

That, I think, provides even further evidence that there's something special about twitches in early development. And that's guiding us now in the work that we do.

Rebecca Spencer, Professor, Psychology and Brain Science, University of Massachusetts, USA explains the research.

Some people are night owls, but I'm very much the opposite. I'm a lark. I like to get up early in the morning. It's the time where I'm very clear-headed, I can see through my problems really well.

The benefit of a clear good night's sleep with a fresh morning run, it's definitely when I think the best. I feel like I got into studying sleep accidentally.

My research background was in learning. In about the mid-2000s, I was a postdoc at UC Berkeley as a neuroscientist.

I remember this study coming out saying that sleep deprivation in young adults is bad for the memory, and that sleep itself was doing something good. That was really novel and somewhat revolutionary.

And because of my background, I was in a good position to be able to look at that. But I want to understand how does sleep make learning and memory better?

When we started this project, studying babies, there wasn't much that had been done in relation to sleep. They really weren't things that would get to the heart of how important sleep was for memory. We know that infants need a couple naps a day, so in our study, we wanted to find out if naps are essential to protecting the memories.

So we devised this experiment starting with nine-month-olds, and we teach them this task, which for an infant means to show them how to play with toys that they hadn't seen before.

They are shown eight toys, and four of those toys we play with in a certain way. Not the regular action an infant would be expected to take. Then we give them back those toys to see if they remember the actions we performed with the toys.

After the first step in the experiment, we record brain activity. That's when the fun begins for me as a neuroscientist to really understand whether sleep has an impact on their memory.

After that, we have two scenarios.

In the first scenario, the babies are kept awake during the time when they would normally be napping. And we then see if they remember the actions we performed with the toys.

It does seem like there may have been a decay in memory here. When that baby skipped naptime, he didn't remember any of the objects.

In the second scenario, we let the babies take their normal nap. We let them sleep, and then, when the infant wakes up, we can see whether they remembered those toys.

So what we're seeing in this study is that the infants are remembering more of those toys, or what we did with the toys, if they took a nap versus when they stayed awake during naptime.

And then we get the exciting part of really digging in and trying to make sense of it. What was sleep doing to the brain that is so important for memory?

And so these waves here is a recording of just the brain activity, um, during sleep. And these bursts you can see stand out from that record. Those are called "sleep spindles." They happen simultaneously across the brain, which provides a good mechanism for the brain to take information from short-term memory area, called the hippocampus, and relocate it in the long-term storage, called cortex.

And that simultaneous burst of activity is thought to support the idea that the memories could be moved out from the short-term hippocampus storage out to the longer-term storage by simultaneously firing all of these different parts of the brain at the same time.

But in an infant, their hippocampus is smaller. So babies need to sleep in multiple sleep bouts, two naps and that overnight sleep, because they have to take that information that's piled up in their short-term storage and move it to its permanent location more frequently than we do.

These are the kinds of results I get excited about. It struck me as a scientist, it struck me as a mom. Naps are important, and we need to value the time that the infants are spending sleeping. Yay!

It's not only something that is that downtime for a mom to take a break, but that it's actually serving a function for these infants. It's when they're laying down those memories that are the foundation for everything that they go on to do.

Closing statement from Rebecca.

Whether you're getting your sleep during your nap or getting your sleep overnight, to overall be maintaining your essential sleep need is really what it's gonna take to both stay healthy, but also to think clearly.

So sleep continues to be important for both our cognitive health, but our emotional health, our mood, and really just how we're able to perform during the day, whether we're infants or adults.

Closing statement from Mark.

Sleep has been perennially described as a period of detachment from the environment, but our work suggests that sleep is a very dynamic process with all kinds of changes in neural activity throughout the brain, changes in behavior. And so sleep is a much more multi-faceted process than has generally been thought about in the past.

Closing statement from Andre.

Sleep is designed for the brain to actually tackle that immensely difficult problem. To learn about the world. And so, that's what your baby is doing when it's sleeping. It's solving one of the hardest problems in the universe. We should let them sleep.

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