The brain keeps some things in the left side and other things in the right side. One side is analytical, the other is intuitive. A third process, “Insight”, the “Ah-ha” moment shows how insight responds. The speed of an individual brain is another realm and that’s measured by IQ but IQ is more than just speed. It’s quality too. Then there are brains that work better for some things but not others. Athletes for example have great physical skill but underlying that skill is are the intellectual abilities that make it possible. Smart people may be smart according to IQ tests but not so great at sports. Usually smart people are better at everything compared to those who aren’t as smart but there are many, many exceptions.
How the brain puts all that together, how all that works is still fraught with mystery.