I’ve been told that the white matter in a brain is fully developed at 20, the gray matter at 8. Why do they say the prefrontal cortex isn’t developed until about 25?

Question

What is there left to develop at 25 if the gray and white matter is done by the time you’re 20ish?

In: 7

Answer 1

It’s not that the grey and white matter are fully developed at 20, it’s more that their volume is the highest at that age, but higher volume doesn’t mean optimal function.

Your brain is a plastic organ, neurons can do and undo synapses (connection with other neurons) all through your life which is needed to learn new stuff and process information and so on*.

Until you are around 25, your prefrontal cortex do work but has a lot of different outputs that aren’t fully mature and do not fully function, it’s just like if you have 24 hours to do 24 things you would take 1h/thing but the ideal would be 2h/thing to do it right.

From 15-25 (around) your prefrontal cortex go through this rewiring where synapses are slowly unmade/made (mostly unmade, it’s called pruning) in order to establish strong long term effective neuronal network that will mostly stay the same all through your life and carry good functions like proper behavioral inhibition in order to reach for a goal for example : It’s like instead of 24 things, you only have 12 to do so you can take 2h/thing and be more effective.

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^(*) ^(After 20 years old or so this plasticity is, however, fairly low compared to what it was and it makes stuff like learning languages or skills harder (although not impossible))

Answer 2

The VOLUME is fully grown but it’s not fully developed. Think of a lanky teenager, he’s not going to get taller but he’s not really fully grown till later.