Answer to Question 1
An alternative approach to studying the brain suggests that neural efficiency may be related to intelligence. Such an approach is based on studies of how the brain metabolizes glucose (a simple sugar required for brain activity) during mental activities. Higher intelligence correlates with reduced levels of glucose metabolism during problem- solving tasks. That is, smarter brains consume less sugar and hence expend less effort than do less smart brains doing the same task. Furthermore, cerebral efficiency increases as a result of learning on a relatively complex task involving visuospatial manipulations, such as the computer game Tetris. As a result of practice, more intelligent participants not only show lower cerebral glucose metabolism overall but also show more specifically localized metabolism of glucose. In most areas of their brains, smarter participants show less glucose metabolism. But in selected areas of their brains, believed to be important to the task at hand, they show higher levels of glucose metabolism. Thus, more intelligent participants may have learned how to use their brains more efficiently. They carefully focus their thought processes on a given task.
Answer to Question 2
One line of research looks at the relationship of brain volume to intelligence. The evidence suggests that, for humans, there is a modest but significant statistical relationship between brain size and intelligence. It is difficult to know, however, what to make of this relationship. Greater brain size may cause greater intelligence, greater intelligence may cause greater brain size, or both may be dependent on some third factor. Moreover, it is probably at least as important how efficiently the brain is used than what its size is. For example, on average, men have larger brains than women. But women, on average, have better connections through the corpus callosum of the two hemispheres of the brain. So it is not clear which sex would be, on average, at an advantage. Probably neither would be. It is important to note that the relationship between brain size and intelligence does not hold across species. Rather, what holds seems to be a relationship between intelligence and brain size, relative to the rough general size of the organism.
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