Although the relationship between Spearman's IQ test scores (g) and the concept referred to as intelligence can be debated, there is no doubt about the clinical utility of such tests in diagnosing psychiatric disorder. Beyond this, IQ scores say something about human intellect, though perhaps not as much as we'd like.
A study published in the Journal of Neuroscience gives new insight into the biological basis of the subparts of the test, fluid (gF) and crystallizeed (gC) components1. Specifically, using fMRI (a brain-scanning technique which indirectly measures blood-oxygenation and can also be utilized to estimate the size of pieces of brain-tissue), these researchers found that performance on the crystallized component of the test was better correlated with cortical thickness, while the fluid component was better correlated with the magnitude of the blood-oxygenation signal while performing test-tasks.
This finding represents an advance from a study that had previously explored the relationship between overall IQ and the volume/location of grey matter2.
References:
1. Choi YY, Shamosh NA, Cho SH, DeYoung CG, Lee MJ, Lee J-M, Kim SI, Cho Z-H, Kim K, Gray JR, Lee KH. Multiple Bases of Human Intelligence Revealed by Cortical Thickness and Neural Activation. J Neurosci, 28: 10323-10329, 2008.
2. Haier RJ, Jung RE, Yeo RA, Head K, Alkire MT. Structural brain variation and general intelligence. Neuroimage, 23: 425-33, 2004.
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