Learning a second language is far easier for some adults than others because of innate differences in how the various parts of the brain "talk" to one another.
The difference is so striking that researchers can even predict who will succeed in language skills, and who will fail, simply based on brain scans.
It is all to do with how well language centres of the brain communicate when resting. Most learning occurs when the brain is at rest, which is why sleep is so important.
Scientists at McGill University in Canada found that if left anterior operculum and the left superior temporal gyrus communicate more with each other at rest, then language learning is easier.
"These findings have implications for predicting language learning success and failure," said study author Dr Xiaoqian Chai.
For the study, researchers scanned the brains of 15 adult English speakers who were about to begin an intensive 12-week French course, and then tested their language abilities both before and after the course.
Participants with stronger connections between the left anterior operculum and an important region of the brain's language network called the left superior temporal gyrus showed greater improvement in the speaking test.
However, that doesn't mean success at a second language is entirely predetermined by the brain's wiring.
"The brain is very plastic, meaning that it can be shaped by learning and experience," added Dr Chai.
"The study is a first step to understanding individual differences in second language learning. In the long term it might help us to develop better methods for helping people to learn better."
Dr Arturo Hernandez, a neuroscientist at the University of Houston who studies second-language learning and was not involved in the study, said: "The most interesting part of this finding is that the connectivity between the different areas was observed before learning."
"This shows that some individuals may have a particular neuronal activity pattern that may lend itself to better learning of a second language."