The Current - What can brain phases tell us about our stage of life?

Episode Date: December 1, 2025

Scientists have discovered our brain organizes itself differently based on different life stages, with some stages working more efficiently than others. A new study from the University of Cambridge identified five main brain "eras" - child, adolescent, adult, early ageing, and late ageing. We speak with the lead author of the study to find out more about these stages and what this research might mean for mental health and dementia research.

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Hello, I'm Matt Galloway, and this is the current podcast. How many times have you been told that your brain is still developing until you're 25? You have to be careful what you do so you don't harm that development. Or maybe you said that as a way to excuse some more immature decisions. It turns out there's some new science that is making the case that our brains actually have five distinct development stages, and you might be considered in your adolescent phage until the age of 32. Alexa Mosley is the lead author of the study, postdoctoral research associate at the University of Cambridge. She is in Cambridge. Alexa, hi. Hi. You have divided brain development into

five stages, and there are key turning points in the course of our life when it comes to how our brain changes. Just walk us through this. What are those stages? Yes. So we looked at how the brain is changing its connections or what we call rewiring. So this could be strengthening some connections and weakening others. And as you can imagine, this is a quite complex pattern. And so we were trying to identify if we could characterize phases of rewiring where the patterns are relatively consistent. And that's exactly what we found. We found a childhood phase from infancy until about nine years old. An adolescent phase from about 9 to about 32, an adult phase from about 32 to 66, an early aging phase from about 66 to 83, and a late aging phase from about 83 to 90 years old. How did you figure that those were the ages at which things change or that there is a material difference? Yes, so we are looking at averages. So there's nothing magical about the number 32. We are just, on average, it seems to be happening around that age. And really what we can do is we can look at the brain like a complex roadmap.

And as you can imagine, there's many different ways we can quantify how the brain is organized. And what we use as a method called manifold learning, which essentially means we take, think of it actually as maybe cooking, where you have lots of ingredients, we have lots of data, and you put it into this algorithm and you have a simplified result that you can interpret. it. So imagine making a pie from all those ingredients. And that's exactly what we did. We were able to simplify this data down into something that's interpretable and find essentially these curves where the developmental trajectory appears to be shifting. You said this is about the brain rewiring itself in some ways. What is happening in that rewiring in those various phases? So in the

youth, the adolescent phase, etc. What's going on with the rewiring? So there's quite a lot. So I'll stick to just the highlights. From that childhood phase, something that sticks out is that the brain is actually becoming less efficient. And the way you can consider efficiency in the brain is the same way you can think about an efficient way to get to between two places. So a short path and a direct route. And we can quantify that in the brain. And so we see this is actually decreasing throughout this early childhood. And that actually flips around nine years old. And during the adolescent phase, we're seeing efficiency start to increase to a peak at around 30. The adulthood phase is really characterized most, I believe, by the stability that we're seeing.

It's the longest phase of rewiring that we found. And there's not one metric that stands out above the rest. There are changes happening. We actually see efficiency starting to decrease, but there's not one that stands out above the rest. Around 66, we start to see this increase in modularity in the brain. Essentially, what that means is certain regions become more connected to themselves, forming a little group than the entire brain. So it's this segregation process. And then around 83, we see something that we believe might be related to decreasing connectivity. Certain regions become more important for connectivity. So if you can think about if you have a single bus that you take to work every day, but suddenly that bus stops running and now you

have to take two buses. The transfer stop becomes much more important to you now that you have to transfer there than it was before when you had that direct bus. And that's what we think is happening in this late aging phase. A lot of attention in the wake of the release of the study has been paid to the adolescent piece of this. And this idea that you are in this adolescent phase up until you are 32. Many people like to believe that they were an adult much earlier than that. You're not saying that this doesn't mean that people in their late 20s are acting like teenagers. What does it say? Yes, that's a very important point because we actually didn't look at behavior.

And there's many different ways to quantify a phase. And so we are looking at structural changes in the connectivity of the brain. And so essentially what our work is suggesting is that there's this long phase of adolescent-like rewiring patterns where the way the brain is changing its connections is consistent. throughout this phase and distinctly different from other points in a lifespan. This is interesting because one of the other things you've pointed out is that these changes line up in some ways with big milestones in our life, right? Yes. Tell me more about that and how you see that connection between, I mean, later in life it seems

obvious as you know you have more health crises, perhaps dementia onset, what have you. But what else is going on in those milestones? that would line up with those key stages that you've discovered? Yeah, we were a bit surprised to see the level of alignment because we only looked at brain structure. A few of the big points I would say is that nine-year-old turning point aligns with the typical onset of purity. We see this kind of stability through three decades of adulthood

after 30 years old, which aligns with some stability we see in cognitive behavior. personality. Another big one would be about two-thirds of people who will ever have a mental health disorder develop that disorder before the age of 25, with the peak age being around 15. And so we're seeing this adolescent phase from 9 to 32 aligning with that increased risk of mental health disorder onset. Another one to point out would be, as you mentioned, the kind of late aging phases of increased risk for things like dementia that we see maybe in the 60s or late 60s as well. What's also interesting when you take a look at the later parts of life is that in that early aging

phase, the 66 through 83, it's not a sudden decline, right, but a slow shift in how people's brains might be rewiring themselves or might be operating? Yes, definitely. It's not something that is particularly big or even major shifts in the rewiring. It's more of a subtle change. Why does it matter to know this information? I mean, it's fascinating and we're learning more about the brain. But one of the things you hinted at was understanding perhaps the onset of mental health crises. If we know this information, where could that lead us?

Yes. So our work really sets the foundation for what we expect a healthy, typical brain to be doing at any point in the lifespan. And that's really important context because the brain develops non-linearly. There's not one steady progression throughout the whole lifespan. We're seeing these fluctuations in these phases. And that's essential context to understand what we would expect the brain to be doing so that we can understand the boundaries of diversity. So why the brain might be more vulnerable to, for example, mental health disorders in that

adolescent phase, there's a chance that it could be related to the particular pattern of rewiring we see during that phase because there's past work that really sets the foundation. for seeing this relationship between the way the brain is wired and other outcomes like neurodevelopment, mental health disorders, and neurological conditions. You're 27 years old, is that right? That's correct. Still considered an adolescent. Do you feel like an adolescent? I don't feel like an adolescent, but I also don't necessarily know if I feel like an adult,

so I'm somewhere in between. How does doing this research make you think differently about your own brain? we don't really understand how this maps onto individuals because you're looking at averages but I know so many people are kind of grasping at how this could be related to them I would love to hope that I haven't hit my peak yet and we don't know necessarily how that might differ from individual to individual I have to let you go but is there one question I mean the neat thing about this is that it feels like just starting into this is there one question that you still want

answered? Yes, I think for me, I really want to understand how this maps onto the phases of behavior and cognition that we naturally see in people. And I think that's one of the questions that people have been most excited to hear about as well. There's plenty of reason to suspect these two things are related, but we really need more research to better understand this kind of developmental phases of the brain and how that could be related to developmental phases of things like cognition or personality. I hope that when you do that research and it's published, we have the chance to talk again. In the meantime, Alexa,

thank you very much. Thank you for having me. Alexa Mosley is the lead author of a new study on the brain coming out of the University of Cambridge, identifying five major brain phases that humans will go through over the course of our lives.

This has been the current podcast. You can hear our show Monday to Friday on CBC Radio 1 at 8.30 a.m. At all time zones, or you can also listen online at cbc.ca.ca slash the current or on the CBC Listen app or wherever you get your podcasts.

My name is Matt Galloway. Thanks for listening. For more CBC podcasts, go to cBC.ca slash podcasts.