Scientific American Mind has an interesting article in the September issue, called “High-aptitude minds”. The article ponders explanations for how smart brains work, reviewing some research along the way, and a whole lot of confusion. For example:
No one is sure why some experiments indicate that a bright brain is a hardworking one, whereas others suggest it is one that can afford to relax. Some, such as Haierwho has found higher brain metabolic rates in more astute individuals in some of his studies but not in othersspeculate one reason could relate to the difficulty of the tasks. When a problem is very complex, even a gifted persons brain has to work to solve it. The brains relatively high metabolic rate in this instance might reflect greater engagement with the task. If that task was out of reach for someone of average intellect, that persons brain might be relatively inactive because of an inability to tackle the problem. And yet a bright individuals brain might nonetheless solve a less difficult problem efficiently and with little effort as compared with someone who has a lower IQ.
I think this is analogous to trying to use an oxygen meter to work out why Usain Bolt won two golds. One might imagine this would work in some very narrow subgroup (like Olympic-level sprinters), but when you start considering the total range of humanity you’re going to get a lot of noise obscuring whatever signal there is.