We enter old age at 66, at least when it comes to the inner workings of our brain. That’s one of several striking findings from a recent landmark study carried out by neuroscientists at the University of Cambridge, who used advanced magnetic resonance imaging (MRI) technology to study, in remarkable detail, how the brain evolves across the course of our lives.
The various phases of life have always been somewhat loosely defined, but by examining scans of more than 4,000 people, aged between nought and 90, neuroscientists were able to identify key turning points where patterns of connectivity across the brain take on distinctly new characteristics.
“We did this by looking at how the brain wires itself… we know that’s really strongly related to all aspects of cognition,” says Duncan Astle, professor of neuroinformatics in the University of Cambridge’s Medical Research Council (MRC) Cognition and Brain Sciences Unit and co-author of the new study.
Their work revealed that, neurologically speaking, childhood seems to end at age nine, while adolescence persists for far longer than we may have previously imagined, at least in terms of how we think and view the world, extending into our early 30s. Our main adult phase stretches for more than three decades, from our 30s to our 60s. The brain then enters a different phase around 66, which signals the onset of later life.
As Prof Astle notes, the reality is that we will all experience these different shifts: “It’s really about how you can make that as healthy a process as possible.”
So what exactly is taking place during each phase – and what does this tell us about how best to boost your cognitive health?
Jump to your phase:
Phase one: Childhood
(Birth to nine years old)
During the first decade of life, the brain undergoes an explosion of development. In particular, the Cambridge study shows that vast numbers of connections are forged between localised brain regions as we develop the ability to speak, reason and form social bonds.
This particular pattern of development continues until roughly the time of our ninth birthday, perhaps linked to the onset of various hormonal changes which ultimately lead to puberty.
“Your brain is shifting gears, and from there onwards, development proceeds in a different way,” says Prof Astle.
How to protect your child’s brain in the early years
In our increasingly digital world, screens are creeping into households from an ever-younger age. Two-year-olds wielding iPads are now commonplace, with entertainment coming via YouTube Shorts and even TikTok rather than playing with toys. Yet studies suggest that excessive screen time (defined as more than one to two hours daily) before the age of five can disrupt brain development and reduce focus, leading to shorter attention spans and poorer cognitive development.
Ronald Petersen, a neurologist at Mayo Clinic in Rochester, Minnesota, advises prioritising learning and playtime which take place away from screens in the early years, as well as giving social media a wide berth before the age of 10. With some studies even showing that playing with toys – for example, dolls – can help stimulate brain areas linked to creativity and social interaction, this could lead to significant long-term benefits.
Phase two: Adolescence
(Nine to 32)
Throughout history, the distinction between childhood and adulthood has long been defined more by social constructs than innate biology. In medieval England, the Church ruled that girls as young as 12 could marry, while warfare in the Middle Ages was often fought by boys in their late teens. Nowadays, we typically perceive adolescence as ending at either 18 or 21, but the Cambridge data suggest that we don’t establish our adult brain until much later.
In fact, for more than 20 years, our brain continues adding to the many localised connections formed in childhood, with much longer-range connections or “express lanes” between distant brain areas arriving later than previously thought. This is crucial for our developing intellect, as it allows for fast, direct communication between all corners of the brain – a bit like being able to get a direct flight between London and Hong Kong without a stopover – creating the propensity for more sophisticated decision-making, comprehension and memory formation, all of which are required to shape our adult personality.
Because this process takes far longer than once assumed, Prof Astle suggests it might explain why people often find themselves re-evaluating their friendships and romantic relationships in their thirties. “You do a lot of things in your twenties, thinking, ‘I’m an adult now, this is me for the next 50 years,’ and actually you’ve still got a decade of change left to go when it comes to forming how you think about the world and what you want from life,” he says. “We’re realising that lots of the things you do in your twenties are still part of your adolescent journey.”
How to protect your brain health in adolescence
The top tip here is to prioritise real-world friendships and connections over social media.
While the majority of adolescents use social media, Petersen is concerned about how living excessively online during this critical phase (at the expense of experiencing the real world) might impact both personality and emotional development.
“At this stage, the brain is certainly malleable and very susceptible to life experiences,” says Petersen. “But smartphones and social media mean that people with a tendency to be more withdrawn, more introverted, can squirrel away with their device, accentuating a lifestyle that is maladaptive and doesn’t lead to good socialisation. Mental health issues could be amplified in this setting.”
Phase three: Adulthood
(32 to 66)
Following the explosion of brain development over the first three decades, the brain enters a period of relative stability and more subtle changes, but this doesn’t mean that its structure is entirely fixed. As experts point out, the brain continues to adapt in various ways during this phase, both for better and worse.
In particular, the main risk to our cognitive health is a process known as brain atrophy, where the brain begins to shrink, which can commence as early as our mid-thirties.
“The volume of brain tissue reduces over the lifespan, and the thickness of our cortex also decreases as we age,” says Heath Pardoe, an associate professor at the Florey Institute of Neuroscience and Mental Health. “The cortex is the outer layer of the brain, which is responsible for our higher cognitive abilities.”
Some brain atrophy is thought to be driven by genetics, but it has also been linked to lifestyle factors such as poor sleep, a high-sugar diet and excess alcohol. Researchers have found that the more atrophy that takes place in a region known as the medial temporal lobe, which is housed deep in the middle of the brain, the more likely you are to experience premature memory loss.
How to protect your brain health in adulthood
The main focus should be on improving your cardiovascular health and blood pressure by doing at least 150 minutes of moderate exercise per week, whether through running, swimming, cycling, playing sport or working out in the gym. If necessary, so-called antihypertensive medications such as angiotensin-converting enzyme (ACE) inhibitors can be taken to control high blood pressure.
Prof Astle says that one of the key factors driving brain atrophy is declining cardiovascular health, exacerbated by an overly sedentary lifestyle. In particular, he warns about the impact of high blood pressure on the network of small blood vessels that perfuse the brain. “If you’re constantly forcing blood through these very fine vessels at high pressure, that could lead to damage over time,” he says.
Phase four: Old age
(66 to 83)
As we move into our late 60s and 70s, it appears that the brain returns, in some ways, to a more childlike state. The Cambridge study indicated that during this phase, we begin to lose some of the “express lane” nerve fibres which offer longer-range connections between brain areas. Instead, the brain starts to prioritise shorter-range connectivity. Losing these longer-range connections can make it harder to make quick decisions, which often require communication between different brain areas, such as remembering your shopping list.
According to Prof Astle, this could also explain why we tend to become less flexible in our thinking when we reach old age, and why we find it much harder to cope with major life changes, such as moving house.
There could be a number of reasons why the ageing brain has fewer longer-range connections. Petersen points out that the ageing brain is characterised by the accumulation of senescent, or “zombie”, cells – cells that have acquired damage but, rather than dying off and regenerating, go “into retirement” and become dysfunctional. In later life, growing numbers of the brain’s nerve cells, immune cells and stem cells all become senescent, impacting its capability to form new connections.
As we reach our mid-60s, the brain’s metabolism also becomes notably less efficient. Prof Astle says that the brain’s ability to use glucose to create energy, particularly in the frontal regions which are involved in decision-making and problem-solving, gradually declines. With less energy available, he suggests that the brain opts to preserve short-range connections over longer-range ones, which can, for example, make it harder to multitask, as that requires quick connectivity between distant brain regions. “Those long-range connections are more energetically expensive to maintain, and so gradually over time, that’s the thing that you start to lose,” he says.
How to protect your brain health in old age
As well as trying to maintain cardiovascular health, try to improve your sleep quality. This has profound benefits for your health at this age.
Poorer sleep quality has been associated with greater accumulation of senescent cells across the body, including the brain. One of the reasons for this is that insufficient sleep means your brain isn’t clearing away harmful waste products as efficiently, which can cause cell damage.
“There is growing evidence that deep sleep is the period when a waste-clearance system known as the glymphatic system is most active, draining metabolic waste products and harmful proteins from the brain,” says Prof Pardoe. “Good sleep quality is important, and treating sleep disorders which often develop in midlife, such as obstructive sleep apnoea, can make a meaningful difference.”
Ideas for improving sleep quality include losing weight, if necessary, as excess body fat can increase your risk of sleep apnoea, when your breathing stops and starts while you sleep, disrupting your rest. Also, try to stick to a regular sleep schedule, going to bed and waking at the same time. As you enter your 70s, try to avoid daytime naps, as this can make it harder to sleep well at night.
Phase five: Super-agers
(83+)
This final phase of brain ageing is perhaps the most mysterious, because scientists are still not entirely sure what sets “super-agers” – people who remain in good cognitive health into their 80s, 90s and beyond – apart from the rest of us.
There were 60 such people in the Cambridge study, which has provided a few clues. According to Prof Astle, while super-agers do still lose connections between brain cells as they age and experience a degree of brain atrophy, their brains manage to preserve key hubs or meeting points, which still allow information to flow from one brain area to another. It might not be with the same alacrity as in their younger years, yet “this seems to build a resilience which gives these people cognitive longevity,” he says.
So what is their secret? Petersen notes that people who possess this resilience tend to come from long-lived families, with mothers, fathers and siblings who also stayed cognitively normal into later life, suggesting genetic factors.
But there are lifestyle factors too. “Our brain health and physical health are closely linked,” says Prof Pardoe. “Staying physically active and maintaining a healthy weight mean that falls are less likely and less traumatic when they happen, reducing the risk of head injuries and extended stays in hospital (which can affect cognition or accelerate pre-existing decline), for example.”
How to protect your brain health after 83
While retiring to the golf course may seem like the ultimate dream, numerous studies suggest that one of the keys to cognitive longevity is to continue pursuing intellectual goals.
This could involve working part-time, volunteering or keeping yourself busy with different passion projects. This also tends to mean that you’re more socially active, which is also good for brain health.
“People who retain a positive outlook and remain more intellectually active throughout life,” says Petersen, “tend to do better in old age.”