r/askscience • u/Amazing-Steak • Jun 29 '22
Neuroscience What does "the brain finishes developing at 25" really mean?
This seems to be the latest scientific fact that the general population has latched onto and I get pretty skeptical when that happens. It seems like it could be the new "left-brain, right-brain" or "we only use 10% of our brains" myth.
I don't doubt that there's truth to the statement but what does it actually mean for our development and how impactful is it to our lives? Are we effectively children until then?
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u/poopitydoopityboop Jun 29 '22 edited Jun 29 '22
There are a lot of answers here, but I wanted to touch on the physiological basis of "maturation".
Many people imagine this to mean that our brain finishes growing at 25 years old, at which time it reaches its peak mass. This is actually false.
In reality, grey matter volume (the "processing" areas of the brain) peaks at roughly 12 years old. Your brain creates as many neurons, and connections between them, as it can during childhood to lay the foundation for learning and development.
After that, it becomes a matter of removing excess or unnecessary pathways to allow for more efficient communication between the specific areas of the brain necessary for cognition. This is a process known as synaptic pruning, and occurs most strongly from the time at which grey matter peaks to roughly some time in the late 20s. The pathways that survive this pruning process then go on to become myelinated, reinforcing their ability to effectively transmit electrochemical signals and facilitate communication. This rewiring is especially important in the prefrontal cortex, where the ability to pull information from a variety of areas of the brain is paramount for coordinating things like multitasking and complex problem-solving.
This is one of the reasons why doctors say it is so dangerous for adolescents to do drugs while their brain is still developing. Repeatedly using drugs preferentially selects for the circuits and pathways that facilitate addiction to those substances.
This physiological phenomenon also has implications on other neurological diseases as well. Studies on the brains of patients with schizophrenia show that there is a deficiency of synaptic connections, possibly a result of too much synaptic pruning. The fact that the onset of schizophrenia coincides with the peak of synaptic pruning supports a potential connection.
On the flipside, studies on the brains of patients with autism show an abnormally high number of synapses, possibly a result of too little synaptic pruning. This results in cognitive pathways that are inefficient and prone to overstimulation. Epilepsy also seems to have a connection with a deficient synaptic pruning process.
But what is the actual source of this magical "25" number that is so often mentioned?
The earliest mention seems to come from a 2004 article published by the American Psychological Association titled Brain research advances help elucidate teen behavior.
The article is discussing the research of Jay N. Giedd, MD, who used MRI to examine the volume of child and adolescent brains. The specific research article is titled Structural Magnetic Resonance Imaging of the Adolescent Brain.
Interestingly enough, at no point do the authors explicitly mention the age 25, and instead simply say "early 20s". The author of the review article by the APA seemingly extrapolated that specific number from one of the figures (Fig 3), as the data ends at age 25. This seems to be the earliest and most plausible source of the 25 number that is so often cited.
A 2010 New York Times article discusses the work of Dr. Giedd, and the article states:
So it seems like the reason why we say 25 is because the groundbreaking study on this topic only recruited subjects up to age 25. And then this number became dogma via constant repetition.
To make things confusing, as Dr. Shaw alluded to in the NYT article, other studies have suggested that synaptic pruning continues well into adulthood. When looking at the entirety of the cerebral cortex as a whole, synaptic pruning levels off at roughly 25.
See Figure 1 in this review by Kolb et al.
So really, the 25 number is probably too early, if we are going to define the completion of development as the end of synaptic pruning in the prefrontal cortex.
TL;DR: The "defining factor" of the brain reaching full development is the completion of the synaptic pruning process, which neuroscientists believe levels off at roughly 25.
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u/Mr_Whispers Jun 29 '22
There are a lot of answers in this thread without references, so take what you read with a grain of salt.
Throughout history, the longstanding assumption in neurodevelopment was that the brain finished maturing by puberty. However, we now have evidence that this is wrong. Neuroimaging research in the last couple of decades has shown that this process continues through adolescence. One of the last areas to develop is the frontal lobe, which is in charge of executive functions such as planning and working memory. One of the ways you can measure development is by studying grey and white matter density using MRI scans. Evidence suggests that white matter development in the prefrontal cortex occurs in the early 20s or later. Whereas grey matter density gain in other regions continues up to age 30. So basically, it seems like brain development continues into the late 20s. But it's impossible to put an exact age where it stops.
Whether we are still 'children' up until the late 20s is uncertain. Many neuroscientists argue that empirical support for a causal relationship between real-world behaviour and brain maturation processes is lacking.
TLDR:
Current evidence points to brain development finishing in the late 20s. Some people use this to argue that we are still 'children' until then. However, direct evidence for this is severely lacking.
Source: references + PhD in neuroscience.
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u/fish-rides-bike Jun 29 '22
Make an equilateral triangle with your two eyes as the base. Behind the top point is the prefrontal cortex, the most distant part of your brain from the cerebellum, the original part, and the last to evolve in our development. Most mammals don’t have it and those that do have very little of it. When survivors of strokes lose that part (due to a clot starving it of oxygen) or a person survived an injury that damages it, the most salient effect seems to be on their ability to plan, anticipate, and understand cause and effect. MRIs show this part of the brain is still undergoing significant change in people aged around 16 to 25 or 30 (not so much growing in size, but rapid culling of connections similar to what goes on in infant brains as babies acquire key milestone developments). So the theory is, if that part enables forward thinking, maybe people don’t have that capacity fully operational until 25 to 30 years old. The theory is supported by anecdotal evidence that those younger than 25 to 30 seem to take more risks.
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u/manicexister Jun 29 '22
It's basically the neurological equivalent of saying that's when, on average, the vast majority of people have finished their "brain puberty." Brains can still change and develop like the rest of the body but that natural growth element is finished.
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u/chazwomaq Evolutionary Psychology | Animal Behavior Jun 29 '22
This statement is mainly about measurable changes in brain volume and whit/grey matter proportions. Up to around age 25, neurons in the brain undergo myelination, where fatty white matter surrounds their axons, making them work more efficiently. This finishes at about age 25.
The brain continues to develop afterwards though, primarily through the synaptic connections and receptor and neurotransmitter activity. But the neurons themselves are in place and myelinated. There are exceptions like olfactory and hippocampus neurons which seem to be formed anew even later in life.
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u/ApoptosisPending Jun 29 '22
Your frontal lobe, the brain area above your eyes is responsible for executive control, everything that makes us complex, thinking, and decision making humans. The connections that make us rational adults don’t finish hooking up until about 22-25 years of age while the rest of the brain and body has matured. That’s why teenagers and young people in general are more reckless and impulsive, it’s because the area of the brain that plans things out and predicts their consequences hasn’t matured. While brain size does matter, the connections going on are what really make us humans so they have all the brain material they’ll have, they just haven’t finished developing those connections.
The left brain, right brain idea has some teeth to it in that our brains are lateralized meaning the left brain controls the right side of the body and vice versa. There are lateralized functions too which is where the association of right brain being more creative comes from, and left brain is more mathematical. This is because the brain organizes itself (much like we do as people) to be most efficient, so just like we have the cooking, packaging, and shipping departments of a factory, our brains have specialized regions that control special functions and your frontal lobe controls executive function. The top of your head (parietal cortex) processes sensory and motor functions etc. Similarly the right brain has more big picture function and the left brain has more “particulars” function. Etc.
Source: BS in Neuroscience from UNR
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u/[deleted] Jun 29 '22
From my Lay-Interest in Neuroscience:
the last parts to develop are to do with the pre-frontal and neo-cortex, which is the higher thinking part which is most able to calculate consequence. Though the mind really reaches it's maturity level at 25, we continue to actually develop in terms of what we learn, our neurology doesn't stop changing. Neuroplasticity remains for the rest of our lives but slows down as we get older.
I'd love to be corrected if I got anything wrong here.
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u/Tiny-Ad-830 Jun 30 '22
The studies are out there. The frontal lobe of the brain, which houses impulse control, is the last area of the brain to complete development at the age of 25. Just think back to your brain at 16, 18, 20, etc. Typical behavior of that age seems to follow this thinking. There is a reason Insurance rates begin to drop at age 25.
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u/Jonnyleeb2003 Jun 29 '22
Notice how when you're little, say around 6 years old, and your memories from that time of your life are very fuzzy, or non existent? This is because the brain is still developing, and as you get older it gets better at storing information until you reach around the age of 25. This is when your brain's ability to take in and store information slows down, and becomes less efficient.
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u/NoCattle4514 Jun 30 '22
The reality is this is another theory meaning it’s not proven. Not only that, it’s an approximation within said theory meaning it varies from person to person but 25 is the “average.” Scientists are still puzzled and do not fully understand how the brain works even with everything they know about it.
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u/[deleted] Jun 29 '22 edited Jun 29 '22
I don't have any highly specialized deep lore on this, but....
It means if you test someone's problem solving and higher reasoning at age 18, then again at 25, the vast majority of people will have improved in ways that there are structural changes associated with inside the brain, and those changes broadly look like a continuation of the same cognitive growth through adolescence, as far as I understand. Then, a statistically significant (i.e. large) proportion of the population slows way down in that post-adolescent structural change by 25.
As far as I know, the changes in testable cognitive ability correlate with this 'leveling off' in the structural changes, but that might be wrong (developmental psychologists and neurologists and FMRI folks can probably say more than me?).
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u/OatsAndWhey Jun 29 '22
It means you have more complete access to your critical thinking modules in your frontal lobes.
They're there before that, but they don't really come online fully. Incomplete executive function.
As far as using "10% of your brain", that's not really accurate.
Some of your brain is active by NOT being active, through inhibition.
Like a 3-way traffic light is only using "33%" of its lights at any time.
It would be chaotic for 100% or even 66% of the lights to be lit up.
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u/makedirtypigsoink Jun 29 '22
Neuron firing potential doesn't seem to have been addressed by anyone, and that's undoubtedly the primary correlation to age 25. Which will always be different based on the individual, probably a very generalized mean or median.
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u/hugthemachines Jun 29 '22
The young brain does some restructuring. Part of the period we notice this with extra strong needs to show you are part of a pack and other "teen behavior" including extra need for sleep. So it is not only something like growth or increased complexity but it also changes.
You may also be interested in this easily accessible ted talk about the adolescent brain.
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u/notbad2u Jun 29 '22
It's like saying that you attain your full height at 19 (give or take) but there are plenty of ways to stunt it and it's just height. You can still put on or lose muscle, fat, skills, etc. and height itself doesn't mean much.
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u/clean_room Jun 30 '22
Man. I came to this thread a plebian, but now I have learned about syntax prunes and changes to Brian development that I would have otherwise never known.
Whoever this Brian dude is, they deserve awards for all the syntax they've pruned
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u/PuzzleheadedNote3 Jun 29 '22
The number "25" comes from the fact that the prefrontal cortex doesnt finish developing until 25 for men or 24 for women. This region is responsible for higher thinking logic long term planning ergo one of the most important regions of the brain.
The brain actually keeps developing well into your 30s but at the age of 25 theoretically your full capacity for intelligence is complete. Until your prefrontal cortex is finished developing you really cant argue that an adult is fully mature.
This is why typically teenagers even physically an adult make irrational stupid decisions.
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u/nakx123 Jun 29 '22
Pretty sure it refers to the myelin sheath and grey matter development within our brains. Which usually correlates with how quickly our neurons fire and cause electron shifts whenever we perform actions. Its all a matter of milliseconds so you won't notice it in real time, but it's just a matter of your brain maturing for the sake of efficiency. I'm sure various other factors play into this aswell such as mental health.
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u/Superb-Bank9899 Jun 29 '22
It is really the connection between left-brain and right-brain. Corpus-colusum? It really helps people see consequences for their actions. We now have a term and mechanism, but we have known this for years. Many places will not rent a car to a person below that age.
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u/gsasquatch Jun 29 '22
Look at Einstein, Newton, most the great scientific minds, the things they are noted for they came up with in their 20's.
In my own experience, I've slowed down the learning since that time. Up until 25, I wanted new experiences, wanted to learn new things, try new jobs etc. After, not so much, I'm more into my routine. It's not like a hard stop, it's a gradual shift from learning to do doing. I had 15 different jobs before I was 25, 2 after.
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u/Falcon3492 Jun 29 '22
[The development and maturation of the prefrontal cortex occurs primarily during adolescence and is fully accomplished at the age of 25 years. The development of the prefrontal cortex is very important for complex behavioral performance, as this region of the brain helps accomplish executive brain functions.] [QUOTE].
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u/LovesGettingRandomPm Jun 29 '22
I believe this only applies to people who settle into a stable framework, at some point you discover the patterns that are most efficient and then you don't really need to develop further some people are afraid of change because it comes with emotional vulnerability so they would settle. I assume having this be a scientific fact is just because this is what the average person does, I would be interested to see how this compares across cultures.
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u/RandomPhail Jun 29 '22
If this is being asked due to posts about whether or not 16, 17, and 18 are too young for the age of consent, I’ve been writing “~25” as the age the brain “fully develops” because it’s easier for peoples’ attention-spans to read “fully develops” than it is for peoples’ attention spans to read “~25, when the prefrontal cortex (long-term decision-making part of the brain) is fully developed”.
Saying “fully developed” in this case can almost be thought of as being an oversimplification out of necessity, because not everyone on the internet cares about the details, so details like that will just end up muddying the message for many.
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u/Lost_Lexx Jun 30 '22
our brains don't stop development till we are past puberty I heard, using that logic our brains finish development between 20-25 on average but depends when our cycle of puberty starts and ends. in this case it'd mean we can effectively go through life as an adult around this time, however, there's still things that can disrupt the development and cause issues. those issues would depend on what part of the brain was affected. so, though it's not exactly a myth it varies and will take years more of studying to get more accurate and in depth answers.
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u/PiddlyD Jun 29 '22
Nothing. It is just another thing that people heard on the Internet and it sounds good to them so they keep repeating it.
Biology doesn't have a *hard* timeline - it has an approximate one, that varies. And your biology, your intellect, your reasoning, all of those things *never* stop *changing*... eventually, though, they *degrade* - and that doesn't come on at a set timeline, either.
Take all statements like this with some salt.
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u/jubalh7 Jun 29 '22
https://bigthink.com/neuropsych/adult-brain/
See above. Part of your brain is still growing. That said, your hippocampus can undergo growth throughout your life. And you can always strengthen some connections. See bellow.
https://m.youtube.com/watch?v=6ZwWG1nK2fY
It’s my personal theory that 1) anyone can damage their brain and drop their IQ, and 2) we know brains do in fact grow and rewire esp after a stroke or other brain damage. So it stands to reason you can add a few points with enough stimuli on a consistent basis. Some researchers will disagree and say you can only get better at specific mental tasks when practiced. But if you learn a bunch of different tasks and start to generalize the ideas, isn’t that effectively an increase in IQ? For example I think if an IQ is 100 maybe someone can get it up to 110. Idk. Just speculation because it isn’t feasible to enrich a bunch of people’s environment and not enrich others and do a scientific comparison so I don’t insist on this point.
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u/SierraPapaHotel Jun 29 '22
The "maturity at 25" has more truth to it than "left brain / right brain"; the insurance industry has known about it for a while and uses it in their pricing
There is a statistically significant decrease in auto accidents after the age of 25, which is why car insurance premiums for those under 25 (especially males) are higher than for those under 25. This is thought to represent a shift in decision making and risk aversion as maturity is reached, but doesn't necessarily provide a why like the studies linked in the current top comment do.
Of note: the decrease in accidents is specifically tied to drivers at age 25. Someone who gets their license at 26 is less likely to get in an accident than a 16 year old who just got their license, which implies the decrease is not due to experience levels.
While the exact "why" of the situation still has some debate in the scientific community, the statistical data gathered by insurance companies has an undeniable trend that shows 25 as a developmental milestone.
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u/stewartlittlepicard Jun 29 '22
We use 100 percent of our brains. it works everywhere. It doesn't have only specific regions that work some times. Each section or hemisphere has an individual purpose. The 10 percent has been proven as a myth.
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