JOHN YANG: When a baby fusses or cries exhausted, parents may wish they could know what's going on inside their baby's brain.

When our scientists hope clues could come with the help of a wearable brain imaging device.

It looks like a cap and can track cognitive functions, and one day, it may help identify early signs of autism or ADHD.

ITV science correspondent Martin Stew has the story.

MARTIN STEW (voice-over): It's easy enough to tell when babies like Victor aren't happy, not so easy to know exactly why.

They can't talk to tell us what's going on inside their head.

And brain scans until now have often involved full sedation and an MRI that's where this wearable scanner comes in.

LIAM COLLINS-JONES, University College London: The cap has lots of these hexagons in it that shine light into the head and measure how much light reflects back off the brain.

And so by seeing the differences in levels of light that reflect back off the brain, we can map where brain activity is happening in the brain.

MARTIN STEW (voice-over): The beams, whilst completely harmless, are illuminating by comparing brain activity with and without social stimulation, scientists observed different levels of activity in the prefrontal cortex, suggesting babies as young as five months old are already becoming emotionally intelligent.

EMILY JONES, Birkbeck Baby and Toddler Lab: So one of the things that we see is much greater activation in social situations.

Some areas of the brain are much more active when babies are watching people singing to them or talking to them than they are when they're looking at toys.

LAURA CHATTEN, Victor's mother: And that's really interesting, how early it is, because hopefully they can't talk to us.

And you know, you pick up on these cues, but you -- it's so interesting to see it lit up, how the brain lights up.

MARTIN STEW (voice-over): Victor is nearing his first birthday, but the kit is light enough to work on babies as young as one month, mapping different ages and different conditions.

What's the potential for this in the future?

I'm thinking particularly around neurodiversity.

EMILY JONES: Yeah.

So one thing we hope to be able to do is use this in infants.

You have a family history of autism or ADHD, we can pick up signs earlier that brains might be developing a little bit differently.

That might help us think about what kinds of support children might need.

MARTIN STEW (voice-over): Scientists from UCL and Birkbeck say the opportunities are endless, but are offering no promises they'll work out how to get your baby to sleep through.

JOHN YANG: That was Martin Stew of Independent Television News.