Males and females acquire language differently: it has been well documented in children, where on average girls tend to speak earlier, with greater complexity, than boys. We also know that animals differ by sex in the ways they communicate. Now a new study from the US may go some way to explaining why, because it finds that the brains of male rat pups contain more “language protein” than their female counterparts, while in humans it appears to be the other way around, boys have less than girls.

The team behind the investigation, from the University of Maryland School of Medicine, writes about the finding in the 20 February online issue of The Journal of Neuroscience.

McCarthy, a professor with a primary appointment in pharmacology and Chair, Pharmacology & Experimental Therapeutics, at the School, says in a statement:

“This study is one of the first to report a sex difference in the expression of a language-associated protein in humans or animals.”

“The findings raise the possibility that sex differences in brain and behavior are more pervasive and established earlier than previously appreciated,” she adds.

The language protein McCarthy and colleagues studied is called Foxp2. Previous studies have already shown that this protein plays a key role in the development of speech and language in children and also in vocal communications in animals and birds.

For their own study, the team wanted to investigate if there was anything about Foxp2 in the developing brain of young animals that might explain sex differences in communication.

To find out, they analyzed levels of the protein in the brains of four-day-old rat pups and related them to the levels of the ultrasonic distress calls they make when they are separated from their mothers or brothers and sisters.

They found significant differences in the female and male pups. The males had more Foxp2 in their brains, in regions linked to emotion, vocalization, and cognition.

And the males were also more vociferous than the females: they called neary twice as frequently as the females during the five minutes they were separated.

The researchers also observed that the mothers always retrieved the noisier male pups and took them back to the nest first, in preference to the less vociferous females.

The researchers also tested what happened when they reduced Foxp2 in the male pups’ brains and increased it in the females’.

The results were as they expected: it was role reversal of the sexes. The female pups sounded like male pups, and the males like females; the mother also reversed her behavior, and returned the females back to the nest first.

In their paper, the authors conclude:

“Our results implicate Foxp2 as a component of the neurobiological basis of sex differences in vocal communication in mammals.”

They then extended their findings to humans, by looking at the initial results of a study in a small group of children.

Here they found the opposite situation to the rat pups.

In humans, it seems that girls have higher brain levels of the language protein:

“We extended these observations to humans, a species reported to have gender differences in language acquisition, and found the amount of FOXP2 protein in the left hemisphere cortex of 4-year-old boys was significantly lower than in age-matched girls,” write the authors.

Cheryl Sisk, professor and Director of Neuroscience Program in the Department of Psychology at at Michigan State University, also studies sex differences, but was not involved in the study. She comments:

“At first glance, one might conclude that the findings in rats don’t generalize to humans, but the higher levels of Foxp2 expression are found in the more communicative sex in each species.”

Funds from the National Institute of Neurological Disorders and Stroke and the National Institute of Mental Health helped finance the study.

In 2011, researchers reported a study where they discovered the gene that codes for the Foxp2 protein acts like a “genetic dimmer switch” that regulates wiring in the developing brain by controlling the products of other genes.

Written by Catharine Paddock PhD