Are animals with larger brains more intelligent?

Challenging the belief that people with larger brains are more intelligent, scientists have found very similar levels of intelligence in rats and mice, a result that could have powerful implications for researchers studying complex behaviour and learning.

Most biologists assume that rats with larger brains are smarter than mice.

Scientists at the Cold Spring Harbor Laboratory (CSHL) systematically compared how rats and mice learn to perform a moderately challenging auditory task and found that their performance was similar.

"This was a task that tested perceptual ability as well as adaptability. We were surprised to see that mice and rats performed about the same," says Santiago Jaramillo, a former postdoctoral researcher in CSHL professor Anthony Zador's lab and who now heads his own lab at the University of Oregon.

The researchers were able to find only one difference: rats learned somewhat faster than mice.

According to Zador and Jaramillo, the training protocol which was developed and optimised specifically for rats might account for the slight advantage.

The finding of roughly equal intelligence has broad implications for cognition research.

"We have found that mice, and all the genetic tools available in them, can be used to study the neural mechanisms underlying decision-making and they might be suitable for other cognitive tasks as well," Zador noted.