Thanks for your comment! Actually, brain function is happening throughout the brain, all the time. What you may be thinking of is that the "gray matter" of the cortex, the outer and "youngest" part of our brain, has its cell bodies in the outer layers of the cortex. This is what gives the outer part of our brain, the cortex, its "gray-ish" colour. But this is just part of the brain's function. Cell bodies send their messages to other parts of cortex and the deeper parts of the brain over the "white matter" connections in the deeper regions. You need the whole thing working together to have any function at all. You are right about the folding of the brain's surface -- this does give a lot more surface area and it what us allows us to have a much bigger brain than our skulls would otherwise fit. Not only that -- but we've learned from computer simulations of brains -- "neural networks" -- that our processing power is not only greater with a larger brain, but the very 3-D nature of our brains -- not just the surface, but the inner structures -- lets us do things (like conceptualize) that we otherwise wouldn't be able to do with a flatter brain. The brain is an awesome thing, eh?