Babies learn to cry in the womb

When infants are born, some aspects of behaviour are ready to go right away while others take time to develop. Clearly embryogenesis is prioritising the maturation of some processes and neurological pathways over others. Crying and vocalising is one of them, because it's critical for soliciting care from a parent, signalling distress and in the bonding process. But most of the work on this has been carried after birth, so relatively little is known about what goes on during the pregnancy. As she explains to Chris Smith, Darshana Narayanan was at Princeton University when she embarked on a study using marmoset monkeys, which develop in a very similar way to human babies, to get some insights into how and when language development begins...

Darshana - Often, particularly when people are studying development, behaviours that are found at birth are thought to be hardwired. And so what we wanted to do is dig a little deeper. So these behaviours that are found really early in life, are they appearing mysteriously, or is there a time period before that these behaviours are developing?

Chris - What sorts of behaviours, specifically?

Darshana - In this case, it was communication behaviours. So babies cry on the day they're born. All babies do, human babies do, monkey babies do. And so our question was, how is it that they can cry at birth? What is happening before birth that allows them to cry?

Chris - Is crying something that's hard to do?

Darshana - It is. It requires coordination across many different systems. Your brain, all of your face musculature, your lungs, your vocal chords. And so yes, it is I would say it's a hard thing to do! Often when we think about young animals, we start thinking about them as soon as they're born, but there's a lot happening before they're born. And it turns out that much is developing before birth.

Chris - How did you study it?

Darshana - We worked with the monkey called the marmoset. They're little monkeys that are found in, primarily in Brazil, but now also in parts of Argentina, I think. They are very vocal. They reproduce quite prolifically, have multiple sets of babies a year. We can house them since they're tiny and sort of gregarious in family units. And so we bred these monkeys and then studied the foetuses by doing ultrasounds on the pregnant mothers.

Chris - This is a bit like having a baby scan for a human who's pregnant, isn't it? So what would you, what would you be looking at specifically when you were doing your ultrasounds?

Darshana - We would ultrasound them regularly. We were first looking for indication of pregnancy. Again, very similar to what's done with humans. The system looks very similar. The setup looks very similar except we bribe the mothers with, with marshmallow fluff, which I don't think we need to do with pregnant mothers to get them to lie still! And then once we saw that there was a baby, we trained the ultrasound wand in a way that we could always watch the face of the baby. And then did that almost every day for months and months to study how the facial movements of the baby were changing, and whether we could recognise the vocalisations of the baby marmoset in the foetus.

Chris - So it's basically crying in utero!

Darshana - So it is some form of crying. Where marmosets are a little different from humans is that they produce some adult-like sounds in their infancy. They're kind of contact calls. So when separated from the rest of the group, they produce this sound to make contact with parents or siblings or friends in some case, I guess. And that was the call that we tracked. It's a very distinct call. It can be very easily identified by length, by the number of sequential syllables that happen in the call. And so that is the call that we tracked.

Chris - And you can see that reflected in particular sequences and movements of the facial musculature?

Darshana - Yes, very much. Yeah. We could see that in the infant. We saw that in and to our surprise, and this was what the results of the study was, we saw that in the foetus and increasingly so as the foetus got older.

Chris - Now, when did that behaviour begin to manifest in the foetus when in its development?

Darshana - In this case, I cannot make a very firm statement because we, you know, we start seeing the face musculature at about the face, the architecture of the face at about ninety five days into gestation. And it's hard to tell whether that's because that's when the ultrasound picks it up or that's when you know the baby's actually making these movements. So that's when the first movements can be observed using the ultrasound.

Chris - And how far through pregnancy is that?

Darshana - The pregnancy in total is 146 days.

Chris - We've also done sort of similar scans on human babies. Do they show similar meaningful movements at a similar level of development? Or are these marmosets a bit ahead of what we see with humans?

Darshana - So with humans tracking them continuously, the way we've done in the marmoset is hard, which is why working with a primate is important. But there have been in the last trimester very, very clear evidence that that babies are making cry-like movements and smiling and frowning and doing lots of things that we recognise as expressions of sound or emotion in in infants.

Chris - Presumably this means then that there's, there's some kind of coordinated connection between the nervous system and the facial musculature in order to make those movements in the right sequences in the right sort of way to do this?

Darshana - Yes, absolutely. Absolutely. And the way and the way it happens is a coordination between the brain, the body, and the environment. In this case, space constraint is something that we hypothesised plays plays a huge role in in allowing certain muscles to move and others not. And that prunes the network body plan, tactile receptor distribution, and then of course the networks in the brain. And then it's the dance between these three elements that that for, you know, move development forward.

Chris - Do these movements just begin to happen spontaneously or are they provoked by something? If you play the sound of the mother's call, for example, does that make the infant more likely to make these sorts of movements? Are they reactive or is it just practising?

Darshana - <Laugh> It's it's funny you asked that. We did try, we tried to play play the sounds of mothers to the babies. It, it was, it didn't, we didn't see anything clear. It was hard to do because the mothers themselves would call back <laugh> the sounds and so sort of muddled. But there is good indication in, in all sorts of animals, humans included, that there's a lot of spontaneous movements happening that are not triggered by a stimulus of any kind.

Chris - And what conclusions did you draw from this? I mean, how does this move us forward? Apart from confirming that these sorts of complicated movements that are going to be very useful once a baby is born are being developed early during development. They're not just manifest from birth. Apart from that, what are the implications of what you've found?

Darshana - One of the big takeaways here is the importance of foetal life. We often forget that when a baby is born, it is not zero. There's nine months of development that has happened before. There's a lot happening during foetal development in humans. Almost every sense we have develops in utero. We even have some visual development. We can, you know, we see the, I think our visual system, the development is accelerated much more after we're born. But much of our development happens in utero.