Mouse intelligence measured

Rodent 'g' might reveal genes for intellect.

HELEN PEARSON

Some mice are cleverer than others, say US neuroscientists. Their rodent equivalent of an IQ test might fuel the controversial pursuit for genes linked to human intelligence.

Scientists have long used a factor called general intelligence or 'g' to rate people's brainpower. The measure spans verbal, logical and mathematical tasks - so a person with a big 'g' tends to score highly in all intelligence quotient (IQ) tests, and do well in school and work.

Mice have a version of 'g', according to a team led by Louis Matzel of Rutgers University in Piscataway, New Jersey1. Animals that come top in one learning test often score better on others, they found: a maze champion might be a sniffing sensation too. "Once in a while you come across one that's absolutely stunning," says Matzel.

This might sound obvious - but because the tests are so laborious, few people have examined whether there are general differences between individual animals. Many studies average and compare the scores of groups of mice using one or two learning tasks.

Matzel's results imply that some mice have a general learning ability rather than, say, just being good at navigating or discriminating. This factor seems to underpin around 40% of the difference in task performance between individual mice, Matzel's team found.

Human 'g' also accounts for about 40% of variation in intelligence tests. "It's a terrifically important paper," says Robert Plomin, who studies intelligence at King's College, London. "It's by far the most stringent test of the hypothesis that you can find 'g' in mice."

Sceptics point out that Matzel's general learning factor may actually be a measure of a mouse's curiosity, motivation or athletic ability. "You might be testing what it's easy to test," warns psychologist Howard Gardner of Harvard University in Cambridge, Massachusetts.

G for genes

If the idea holds up, the mouse version of 'g' could help researchers to hunt for genes that underlie mouse learning power and, perhaps, human intelligence. Many studies have shown that 'g' is partly inherited, but it is difficult to track down relevant genes in people.

Matzel is already comparing the brain genes that are active in mice with high and low 'g' values. These might help re-wire nerve cells or boost signal firing.

Many experts are wary of this line of research, however. It raises the prospect that people might be labelled as clever or stupid on the basis of their genetic code, or that parents could screen embryos for intelligence genes.

Geneticists counter that such studies might instead reveal ways in which we can boost intelligence using, for example, nutrition or education. "They are difficult issues - but they're not as worrisome as we think," Plomin says.

Others argue that 'g' is a poor measure of human intelligence anyway. IQ tests, they say, are too crude to pick up individual talents. Gardner, for example, proposes that there are several distinct types of intelligence, such as logical, musical and interpersonal.

References
Matzel, L. M. et al. Individual differences in the expression of a 'general' learning ability in mice. Journal of Neuroscience, 23, 6423 - 6433, (2003). |Article|

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