Why does the brain stop developing after your mid-20s?

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Also, what does it mean when people say the brain is fully developed? Does for example learning a new language become harder after your brain ‘stopped growing’?

In: Biology

Short answer is that it doesn’t, it’s just that most of the connections that are needed for you to survive have been made so less development is needed. However, brain plasticity (the brain re-wiring itself, changing in response to experiences) happens throughout life to a greater or lesser degree depending on how much ‘mental exercise’ you do.

Usually what is meant by “stops developing” is that the brain stops making new neurons. It was commonly semi accepted that this happens at age 25 but a recent powerful and well controlled study shows that brain stops making new neurons at age 13 (at least in one region called the hippocampus where process new memories). There’s a ton of studies out there, some even show the brain continues to produce new neurons well into your 90th birthday. There’s also established evidence of stem cells in the olfactory bulb (where you smell things) which bestows regenerative capacity. And this is all just on neurons there many other cell types in the brain like neuroglia which definitely continue to be produced later in life. So in short we don’t know, but we think that there is a sharp decrease in or a virtually complete cessation of neurogenesis (production of new neurons) somewhere between your teenage and mid 20s, that is why your brain is thought to be fully developed by then.

Learning a new language becomes harder with for many reasons, and reduced capacity of neurogenesis is likely only a part of it. The reasons include reduced plasticity (your brain is less capable of modulating the strength of its connections to store new information or integrate a whole new language into everything you know) and also things like the fact that adulthood is stressful and gets in the way of focusing for a long time as you have a lot on your mind. There’s a lot more to this. But like a muscle, train your brain enough and you can make it better. But also like muscles, the ability to make new cells decreases but that doesn’t mean you can’t strengthen what you already have.