Every time I ask this question, I feel like the answer sidesteps an actual explanation. Yes, I understand that the folded, wrinkled shape allows for more surface area. The heart of my question is WHY is that important? Like, if the outermost layer of the brain is important, why couldn’t it just be a thicker layer instead of just squishing more outermost layer into a wrinkled shape?
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Are you asking why evolution works the way that it does? Because your example might be plausible, it’s just that no creature has evolved that way (to my knowledge) and managed to develop the same degree of intellectual or processing capacity that humans have.
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Wow the other comments are really bad.
The answer is fairly simple: our brains are made up of multiple parts (look up brain regions on Google image) one of the most important is the cerebrum which includes our cortex. The cortex is in charge of many complex processes (eg. Language, social interaction, executive functions such as anticipating or predicting outcomes etc…). This part is like a sheet laid over the rest of your brain.
Now how would you go about fitting a large sheet of paper in a small container ? You might fold it or bundle it, that’s about what happened to our brain.
The folds and creases allow for a bigger surface area — thus more room for more neurons and connections — in a given volume.
The brain case is has only so much room, but you are right. Recent studies show that cortical thickness AND surface area correlate to intelligence, but there is only so much space to squish it all together. A combination of thickness and folds increase total volume and positively impact IQ. Here is an scientific article referencing such a study. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3985090/
The reason the out later is folded and not wrinkled is the need for space. That layer is largely neurons that stick out long fibers to connect to other neurons. Well, that layer absolutely could get thicker, but at a certain point, there wouldn’t be enough space to run those fibers from the outermost neurons to the interior of the brain. The solution to this is folding. Folding allows you to fit more of that outer sheet without having the cramming problem of thickness
Simple straightforward answer, most of our brains processing capacity is done on the surface of the brain. Wrinkles increase the surface area.
But then you’re asking a why question. That’s a lot harder to answer. Why is the processing done on the surface and not more Evenly distributed? Because that’s what evolution converged on. Evolution relies heavily on chance and does not guarantee the absolute best solution.
To answer the other part of your question-why there isn’t just a thicker layer of neurons: part of it is that it evolved that way. Evolution makes changes based on what’s already there, and it would be difficult to make it thicker. There are specialized layers of neurons within that thin outermost layer (the cortex). Making it thicker would either add more layers that aren’t needed, or disrupt the relationship between layers. But the bigger reason is space. You need connections between all those neurons throughout the brain. But increasing the thickness of the cortex would mean an exponential increase in the volume needed to make room in the cortex for those connections. Thus, there wouldn’t be much room to add a lot more neurons.
>…the folded, wrinkled shape allows for more surface area. The heart of my question is WHY is that important?
The more paper you have, the more you can write down. More RAM, more memory, literally. The surface area is the memory. There’s a recent study about brain neurons and more communication. Yes the title is clickbait — there’s nothing hiding, they just didn’t know what it was. [https://www.sciencealert.com/scientists-just-found-a-new-kind-of-synapse-hiding-in-the-brains-of-mice](https://www.sciencealert.com/scientists-just-found-a-new-kind-of-synapse-hiding-in-the-brains-of-mice)
Detail, the thinner something is the more layers it can fold.
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