Children's mental health, and mapping bilingual brains

0:17Hello and welcome to the Naked Scientist podcast, the show that brings you the biggest breakthroughs and talks to the major movers and shakers in the worlds of science, technology and medicine with me, Rachel Ralph. Coming up, experts express concern over a sharp rise in children's mental health referrals. But what is driving the increase? Also, hola, guten tag, konnichiwa. We discuss bilingualism and find out how our brains are able to interpret different languages. Plus, a new study reveals where we might be going wrong when we recycle our household waste.

1:01England's Children's Commissioner, Rachel D'Souza, has warned that the country is facing a crisis after more than one million children were referred to its mental health services. A new report says numbers are up by 10 % on last year, and there are now around twice as many referrals for children and young people than there were eight years ago. But what is driving it? And do we see similar trends elsewhere? I went to meet Barbara Sahakian, a professor of clinical neuropsychology and an expert in ADHD at the University of Cambridge. Barbara has just returned from the International College of Neuropsychopharmacology, or CINP, Congress in Glasgow.

1:42This increases across a number of different mental health disorders, in particular anxiety, but also depression. Those are very common mental health disorders. And then there's also increased diagnoses of autism and attention deficit hyperactivity disorder, or ADHD. And what do we think is driving these? Well, there's probably a number of drivers, and they may be different for different things. I mean, one thing that has been pointed out is, you know, internet use and social media, where people are trying to fit into perfect mold of what they think they should look like and things like that. There's also some bullying that goes on.

2:23And so there's exposure to things like pornography, which young people shouldn't be seeing. So there's a whole lot of factors that way. I work particularly in ADHD quite a lot and there we see that there's a number of different factors including you know the sort of parental styles the fact that we're using technology much more which means we switch our attention very rapidly from you know looking at our phones or looking at something very quickly short videos on our phones and then maybe using the computer or doing something else rather than focusing our attention for long periods of time in order to get a goal done so you know like homework or something really important so that's actually probably producing a lot of problems because it's been shown in studies that if students have their phone and it's they're getting messages or something on their phones during a lecture they don't do as well as people who don't have their phones with them and also even there's a study which shows that just having your phone, even if it's not on, sort of generates the kind of anxiety.

3:29People want to keep checking it, even though it's sitting there and it's off. So there's a lot of that that's causing probably very rapid switching of attention and distraction. And that, of course, is the type of thing that you might see in attention deficit hyperactivity disorder. So one of the statistics that was mentioned by Rachel D'Souza, the Children's Commissioner for England, was that there was almost a 50 % increase since 2018 slash 2019 in mental health problems. So do you think COVID has impacted this at all? It definitely seems to have affected quite a few of the mental health disorders, certainly exacerbated people who already had the symptoms, you know, got worse during that time.

4:12And obviously, you can imagine how maybe obsessive compulsive disorder might have increased because everybody was worried about, you know, catching something and everybody was washing their hands and making sure that everything was, you know, clean. So that may also have effects on that. And anxiety as well, because obviously a lot of people were anxious and a lot of people experienced bereavement during that period. So that would also lead to possibly to depression if you didn't have it dealt with effectively, you know. So definitely there was that. We actually did our own study where we looked at people during the COVID-19 pandemic, and we did see that those people who were less socially connected actually had increased symptoms of depression in terms of negative thoughts and biases, that kind of thing.

5:04And so people really did much better if they had some kind of social connection. I've also written about a very critical group, which is the one to five-year-olds, because that's the time during which social cognition develops. And if you didn't have a sibling during that time, and if your parents were busy, say, trying to work from home or do something like that, and they were actually engaged and couldn't interact with you, but you also wouldn't have had many peers if you didn't have a sibling, they wouldn't have been, you know, developing theory of mind and the sort of sharing and cognitive processes, empathy, the types of things that you develop with social cognition during that period of time.

5:46And certainly teachers have reported that when they come into the sort of nursery and primary schools, that they're sometimes more, slightly more aggressive, and they don't want to share toys. And there's a lot more problems in social interaction. And I guess economic inequalities also play into this, because for those teenagers or children that were at home during the lockdown, if they didn't have access to a good computer or the internet, then they would have also struggled to communicate with friends during the pandemic. Yes, I'm sure that's the case. I mean, they usually do with most things.

6:24One of my favourite studies that I've done was published in Psychological Medicine, and it really looked at reading for pleasure in young children. and those children, and we use the ABCD study database, which is a USA study. And what we showed is that those children who read early in life for pleasure, when they were adolescents, they had better mental health, you know, less symptoms of depression, they had less symptoms of inattention, better school attainment, better cognition, and actually better brain structure. so it's really important and I raised it because we actually looked at socioeconomic status in that study and regardless of socioeconomic status you got the benefits so those children who read for pleasure early had all those benefits that accrued in adolescence and probably they'd keep them lifelong so this very small intervention can be really important later on.

7:23You mentioned this study was in America so the statistics that have been published recently this week are for the UK and are we seeing this increase in mental health problems in other areas of the world as well? Yes while I was in CIMP I did a session with Tom Insel and I mentioned this problem of increasing mental health problems in young people and he said basically the same was happening over in the USA. And are we seeing this with adults as well? Well, I've been focusing on attention deficit hyperactivity disorder, and I'm just about to publish with Christelle Langley a paper in the Journal of Psychopharmacology.

8:03And what we saw was that actually they are rising for ADHD diagnosis and prescriptions. They're rising a lot in adults as well. And the interesting thing is in 2025, that was the first time that it was actually greater prescriptions for adults than for children. So, yes, it's increasing. The other interesting statistic there was we think of it as a neurodevelopmental problem, ADHD. And we know that usually there's four boys to one girl gets diagnosed. but in the adult population it's virtually one-to-one. Barbara Sahakian at the University of Cambridge. Norovirus, which is also known as the winter vomiting bug, is an illness that causes vomiting, nausea, stomach pain and diarrhoea.

8:57It is relatively uncommon but highly unpleasant and contagious, with no approved vaccine or antiviral therapy. In low - and middle-income countries, it kills 200 ,000 people a year and mostly young children. But a recent study identified an antibody, immunoglobulin A, that helps the immune system defend against neurovirus infections. Yale University's Craig Weiland has been telling Chris Smith about it. Yeah, so we're really interested in this virus called norovirus, which is a tiny virus that causes a big problem, which is severe vomiting and diarrhea. It's also commonly called the cruise ship virus.

9:35And the big problem we're trying to address is how can we prevent this virus from causing disease? And ultimately, how can we make a vaccine or a drug to prevent infection and prevent these symptoms? It's a major global public health problem that no one wants. Currently, there's no solutions, there's no vaccines, and there's no drugs for it. It is a big problem, isn't it? Because I mean, if you look at an average country like the UK, it's probably millions of cases per year, most of them, most people are not aware of, because it's a 24 hour thing, isn't it? Short and sweet, but not sweet. Typically, we say that people are getting infected every three to four or five years, Sometimes you don't get symptoms, but across the globe, there's probably 500 to 800 million infections every single year.

10:14There's many different types of human norovirus that cause infection. So it's ubiquitous, but poorly understood. Given that ubiquity, why don't we make a lifelong immune response to it in the same way that if I ran into measles, thankfully, I had a vaccine, but if I ran into measles and caught that, I wouldn't catch it again, probably. Why is it not like that for noro? So first is that there's many different strains of norovirus. So just like influenza, you may have protection against one strain, but a new strain may pop up in a couple of years. And this happened last year, actually, where a new strain popped up that people hadn't seen that much of before, and there were more cases than usual.

10:50The second answer is that norovirus is really smart, and it infects a part of your gut called your small intestine. And here, the immune system works a little bit differently. We found that there's a different type of antibody, which is this really sticky protein that acts like a wet blanket to block the virus from infecting you. And that type of antibody tends to be relatively short lived. So we think that that antibody will stick around for a bit, but then it goes away so that the body's not wasting time making this antibody that isn't needed. And we think that makes people re-susceptible. Now, we do think that when people get reinfected, that they probably do get less severe disease because they previously have some protection.

11:29And this is exactly what we see with COVID. But this term sterilizing immunity, where you get infected once and then never again, And that is just not what happens with norovirus, like many other viruses like measles or rotavirus. What are you doing then to try and realize your goal of actually making this less of an international disease burden? Yeah, so recently a large randomized control trial of the first big human norovirus vaccine failed quite miserably. It was a multi-country study where they vaccinated thousands of infants and the vaccine had 0 % efficacy. and for us this was really a big wake-up call and I think for the field which is we can't make a good vaccine and spend hundreds of millions of dollars trying to to get it to work if we don't actually understand infection and how we can get an effective immune response to protect us against infection.

12:22So we wanted to take a step back and ask actually what are the mechanisms that control infection. And to do this, we used mice. It's because in mice, we could really control infection, we could control the virus, we control the animals. And here we use this to basically make a model of human or virus and ask what are the mechanisms and what parts of the immune system are necessary and sufficient to protect us from infection. What the long term goal is, can we now mimic this with a vaccine in that person? What does it actually do in mice then? What have we been missing in people that you can now potentially see in mice with the mouse equivalent?

12:59In humans, for many, many years, we knew that the major correlates of protection to infection were two different types of antibodies. One type of antibody called IgG, and this antibody circulates in the blood and is really easy to measure. then there's a second antibody that tends to live in our saliva, in our secretions from our airway and nose and in our intestines. And that's a type of antibody called IgA. And typically, if you get infected, IgA and IgG kind of go hand in hand and both go up and both go down together. But we didn't know which one of those, if either was actually essential. So much of the vaccine research was, all right, let's just come up with a vaccine that could boost this blood IgG antibody because it's easier to measure blood than it is antibodies in the feces.

13:46But we didn't know that that was actually protective. So we actually asked which of these is essential. And it turns out that in mice, at least, only IgA was essential and IgG was not. And that was a fairly big surprise to us, given the human literature and the assumptions that we read and others erroneously made over the years. iga is a form of antibody that gets secreted at various surfaces like you say it's it's at our airways it's in tears genital secretions and so on so is the mechanism of defense against noro you're outlining then that the body makes this antibody and it basically splurges it all over the intestinal lining so it's there like a barrier so if the virus does come again the antibodies they're ready to greet it yeah the really cool thing about iga and what makes it special is that there's a little piece of IgA that is different than IgG that enables it to cross these semi-permeable barriers and cross from your blood to your intestines or to cross from your blood to your tears or nasal secretions or breast milk.

14:52And that's what makes it special, and that's what helps it fight infection in the gut before that infection can really take hold and replicate. The hard part about IgA, it's much harder to make vaccines that lead to higher IgA. It's pretty easy to make vaccines that lead to really good IgG responses. And do you think you can surmount that then? We do. We think it will take time and additional research. I think the first step that we identified is now that we know IgA is really important, we can now make this as our primary goal for a vaccine. There are several vaccine approaches that are being tested for influenza, for COVID, and for other infections that are really focused on IgA, but it is a difficult barrier to overcome.

15:32I think one thing that may work is making what's called a live attenuated vaccine, which is a weakened version of the virus. And we have this for poliovirus. We have this for rotavirus. I think that might be the most effective approach for norovirus, but there's a lot of barriers for us to overcome scientifically to be able to get there. And then there's other approaches where maybe we need new vaccine platforms that can actually lead to IGA. And we and others are working on those as well. Craig Weiland at Yale University in conversation with Chris Smith. That study has just been published in Science Translational Medicine.

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16:25music in the program is sponsored by epidemic sound perfect music for audio and video productions this is the naked scientist podcast with me rachel ralph still to come the best way to recycle plastic in a bid to keep it from our seas and landfill sites but first people who speak more than one language know what it is like to express the same idea in various ways and a new study has found that this translation skill depends on a shared mental map of brain activity in an area called the hippocampus. The research, published in Cell, shows that most brain cells respond uniquely to each language, although a few cells respond similarly to matching words, such as the Spanish tierra and the English earth.

17:11Even though brain cells change their responses for each language, the overall pattern or the way ideas connect in the brain remains consistent across languages Benjamin Hayden from Baylor College of Medicine has been speaking with Chris Smith the question here is how does the bilingual brain represent the same information in two different languages at the same time why is that even a question though why why do we think that that ought to be a neurological challenge because we know the brain does it does it brilliantly some people speak multiple, like seven languages. You give an example in the paper of Arnhem Land in north of Australia, where people routinely speak seven languages.

17:49Right. Think about it for a little bit. It becomes really, really complicated, because if you speak two languages, and somebody asks you a question in one language, you're going to know to answer in that language. And if you cross the border into a different country, you're going to know to use that language. So you can keep those languages separate in your mind. At the same exact time, if somebody tells you a story in Spanish, and then they ask you or somebody else asks you a question in English a few minutes later, you can do that translation in your head. So you have a general representation, but it's also a different representation.

18:21And so getting that simultaneous general and different, that's the really hard part. In other words, you can listen to the story in Spanish, but you'll know the answer to an ensuing question in English instantly. So you You must be experiencing the representation irrespective of the language, but both are available to you instantly somehow. Yeah, you can do it the general and you can do the distinction at the same time. You can keep them separate, but you can also let them blend. And that actually turns out to be a really, really hard problem. I suppose in a research perspective, it's also tricky because we are unique in using language the way we do, having the language we do.

18:59and therefore you can't just ask a mouse to do this for you. Right, absolutely. It would be really great if we could stick an electrode in the mouse brain, but we don't have any mice that can speak Spanish or German or any other language. That we know of, apart from Mickey Mouse, possibly. But you have got humans, though. Right. So we have this very rare and special population of humans that have severe epilepsy, chronic epilepsy. It's so bad that it won't respond to any other treatments. They're getting 10 to 50 electrodes implanted in their brain to monitor where the epilepsy is coming from so that the surgeons can treat it.

19:34We come into the clinic when one of these people is a balanced bilingual. And just by chance, we happen to have a bunch of English and Spanish speakers because we're in Houston, Texas. And we ask them to listen to an audio book in English and then the same audio book in Spanish. And then we have them have a conversation with us in English. And then we have somebody who works in our group who has a conversation with them in Spanish. as well. And so we can look at how the brain represents the English and the Spanish. This is by eavesdropping on different nerve populations with those electrodes that are in there.

20:06That's exactly right, yes. And the electrodes are in the right bit of the brain that corresponds to where you're interested in. That's right. These are electrodes that are in the hippocampus of the brain, which represents a lot of the kind of basic structured information that we deal with, including language. And what do these electrodes do when a person's listening to the English story or the Spanish story, what do you see them doing? Yeah, so every single word that you hear elicits a pattern of activation in these neurons. If there's maybe 100 million neurons in the hippocampus, typically about 10 % of those neurons are going to fire in response to any given word.

20:43And some neurons have higher firing rate, these are spiking activity from these neurons, some neurons are going to have lower, and they're going to create a pattern of activity, and that's what we're measuring. And is it the same neurons, regardless of whether it's English or Spanish, that the person's hearing? It had been assumed for a long time that there was going to be a Spanish part of the brain and an English part of the brain. And what we can find, I think, for the first time ever with this study, is that that just isn't true. Not only is it not separate neurons, it's the same neurons, but they're not representing the same thing.

21:15So if I hear the word five, and if I hear the word cinco, which is a Spanish word for five, it's not going to be the same neuron representing that. It's not going to even be the same 10 % of neurons, but the pattern is going to have some similarities anyway. How on earth does that work then? If you've got the same cell lighting up when they hear two different things, or rather the same thing, but it's recruiting different groups of nerve cells, how on earth do we make sense and have that general picture, that general understanding of the story, regardless of whether it's in English or Spanish?

21:48Yeah, that was kind of the hardest part of the study for us. in it. There's a lot of advanced math in it, but I'll try to explain it as clearly as possible. Imagine the word dog and cat. Dog and cat mean almost exactly the same thing. They both have four legs. They both live in your house. You take them both to the vet. And then imagine the word fork. Fork means something completely different. It's used in totally different situations. The pattern of neural activity in the hippocampus when you hear dog and cat is similar. It's not identical because dog and cat aren't the same thing, but it's similar.

22:19So there's a pattern of activation among these hundred million neurons. And the pattern for fork is basically completely a different pattern. So those three things together have a mathematical relationship that describes them. Now imagine your entire lexicon of 100 ,000 words of all the words that you know. That creates some giant web. And the web shape is basically the way that the language is represented in the brain. Your web for English and your web for Spanish have basically the same shape although they're not the same neurons involved so it's if you can look at the shape of that response the shape of that web then you can infer what these words mean so the brain has its own thought process that it has an understanding or a concept or a mental picture and the language that it expresses in or receives information in that lies upstream of that picture so it's like the brain's got a common encoding for what something is and it then has to convert that back out into a language or it receives it via that language but the the actual brain impression of the thing the dog the cat the fork that lies downstream of this interpretative mechanism i think that's that's exactly right yes now we know this what does this unlock for us apart from being academically extremely satisfying that we've got a bit further down this pathway that that was previously a closed door to us.

23:42What can we do with the information you've now elicited with this? The real goal here is to understand how concepts are represented in the brain and how thoughts are represented in the brain. And we see language as a tool for studying that. But ultimately, what we really want to do is treat diseases like Alzheimer's disease, where people either lose their concepts, conceptual representation, or they have them, but they lose access to them. And we want to figure out how to recover those. In order to do that, we need to understand this very basic thing about how thoughts and concepts are represented in the brain.

24:17Benjamin Hayden at Baylor College of Medicine speaking with Chris Smith, and that study was recently published in the journal Cell. Recycling gives our old stuff a second life, and it keeps out of landfills and oceans. When it comes to recycling, we usually have two options. One is source separation, which is sorting our waste at home. The other is post sorting, where everything goes into one bin and is sorted at a facility later. A recent study looked at both methods. Post sorting can catch more plastic, but it also lets in unwanted materials such as dirt, moisture and even dangerous metals like lead and cadmium.

24:56These make recycling harder, lower the quality of recycled materials and can even be risky to our health. The researchers say post-sorting is helpful, but it can't replace sorting at home. Stephen De Maester from Ghent University shares his findings with Chris Smith. Plastic recycling rates in general are too low all around the world, below 10%. And what we see from every analysis is that how much plastic we collect for recycling is the most sensitive parameter to really increase the recycling rates. Well, there are two ways of collecting plastic waste. Either there is what is called source separation, which means that inhabitants of a country separate their plastic packaging like bottles, trays and films in a separate bag or bin, and then it's separately collected.

25:43And then later it goes to a sorting plant where these bottles and trays and films are separated from each other. The other way is post-sorting. And post-sorting means that the inhabitants and the households bond to the sorting. and throw everything in a residual bin. And then this residual bin is collected and then machines try to separate the bottles, trays and films out of mixed waste. But of course, that mixed waste then contains other items like textiles, a lot of organic waste and so on. Now, if we want to increase the recycling rates in the world, we need to get more plastic out of the waste and more collection.

26:21What you see is that some countries do this source separation already very intensively, like Belgium. But other countries, for example, in the US, it's not a habit to do this separate collection. And there is a big debate in countries and waste management communities, should we introduce more separate collection or can machines do it? And countries that don't do this source separation should just invest in more machinery to get the plastic out of residual waste. So what we wanted to do is put some evidence on the table. Does it now make sense to do this source separation or shall we trust the machinery to sort it out of our residual waste and don't bother the inhabitants to do this source separation at home?

27:04The ultimate goal then is to try and drive up that pretty dismal rate of recycling of plastics. I'm quite frankly shocked it's as low as 10%, especially judging by how much goes in in my bin at home. I mean, obviously, one thing to do is to cut down the amount we use in the first place, but that's a different story. and the question then is well do we get people to do this at home or do we get machines to do it what's going to translate into the bigger number that's effectively your starting point isn't it what's going to get us a superior amount of recycling whether we get people doing it or machines doing it exactly that was the setup of the study and important in plastics is that it's not only the quantity that matters but also the quality that matters so i can for sure agree that post-sorting ramps up the quantities of material available for recycling.

27:57But the quality of the material is super important and it should be safe. It should have the right colors, should have the right properties. So it's also a lot about quality of the material that comes out of the system and not only about quantity. How did you do this then to try and get a handle on what would happen if you had a policy where we just get machines to do it versus a policy where people do this at home more? So what we did, we went to a sorting plant in the Netherlands that takes both source-separated waste and post-sorting where the machines try to separate it from residual waste.