ASK a physicist what g means and the answer is short and sweet. On Earth, the acceleration due to gravity is about 9.8 metres per second per second, though it varies depending on how far you are from the planet鈥檚 centre of mass. Ask a pyschologist the same question and the likely answer is: 鈥渉ow long have you got?鈥�
For a psychologist, g stands for general intelligence, a mysterious measure of human behaviour. Whatever IQ tests measure-spatial or verbal ability, memory or information processing speed-people who are good at one type of test tend to be good at the others too. These abilities seem to have something in common, and with the right statistical tricks you can pull out that common element. This is g.
It鈥檚 when you ask exactly what g measures that hand waving begins. It could be a coming together of a whole raft of cognitive processes, or something more singular such as the speed at which the brain processes information. There鈥檚 no doubt that g is abstruse, but it does have some intriguing-and useful-properties. Experts reckon that it stays more constant after childhood than other behavioural traits, and that it can predict educational and occupational levels far better than any other measure.
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The story of general intelligence took a new twist last week. John Duncan and his colleagues from Britain鈥檚 Medical Research Council Cognition and Brain Sciences Unit in Cambridge announced that they鈥檝e found a part of the brain we are mightily tempted to call the g spot (Science, vol 289, p 457).
The researchers used a PET scanner to study brain activity in people as they carried out two kinds of cognitive test. One set was known to provide a good measure of g, while the other did not. Their results show that tests linked with g light up the lateral frontal cortex, an area of the brain around each temple.
So does this tell us anything new about the nature of general intelligence? Not really. Duncan and his colleagues conclude that g is confined to one part of the brain. (But as they acknowledge, this large, ill-defined area may be performing many different functions.) They go on to imply that their finding supports the idea of g as a discrete thing that underpins many of our cognitive abilities. This remains highly contentious.
Most importantly, the work tells us nothing about the things we really want to know: what鈥檚 going on and how? It does not tell us what intelligence is, how it relates to creativity or the link between IQ scores and how easily people solve real-world problems.
Still, it is intriguing that after more than 2000 years of searching, researchers claim to have found the seat of at least one form of intelligence. And anything that tries to put such a controversial concept as IQ on an objective footing has got to be welcomed. Psychologists and neuroscientists reckon that Duncan鈥檚 study will spark a research-fest on the lateral frontal cortex. 杏吧原创s will want to look again at which genes are preferentially expressed there, and how people with damage to this area are affected.
So even if this research does not itself resolve the mysteries of g, it could well trigger research that finally does.
