Previous research has shown that larger brains are weakly related to higher IQ, but this study is the first to demonstrate that gray matter in specific regions in the brain is more related to IQ than overall size.

Gray matter, so named because it looks gray to the naked eye, is composed of numerous neurons and blood vessels, and is the major part of the nervous system in which nerve impulses for all kinds of mental functions are produced.

To study the relationship between gray matter and intelligence, Haier and colleagues enlisted 47 normal adults. Using a technique called voxel-based morphometry, they determined gray matter volume throughout their brains, and then correlated these results with their IQ scores.

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