Male Rat Pups have Higher Levels of Language Protein than Females

Girls tend to speak earlier and with greater complexity than boys of the same age. But a new study on rats shows that male rodents are more vocal than the females, suggesting that the differences may arise from different levels of a specific protein in the brain.

Scientists have long debated the origin and significance of gender differences in early language acquisition and development. Studies have already shown that a protein called Foxp2 plays a significant role in speech and language development in humans as well as vocal communication in birds and other mammals.

In this new study, researchers at the University of Maryland School of Medicine examined whether gender differences in the expression of a specific brain protein might lead to communication differences between the sexes.

The research team analyzed the levels of Foxp2 protein in the brains of 4-day-old female and male rats. They compared it with the ultrasonic distress calls the animals made when they were separated from their mothers and siblings.

The male rodents had more of the Foxp2 protein in the developing brain areas associated with cognition, emotion and vocalization. They also made more noise than the females by making nearly double the total vocalizations over a period of five minutes that they spent away from their moms, who preferentially came and retrieved the pups.

In another experiment, the researchers reduced the levels of Foxp2 protein in the male rodents and increased it in female pups. This time, the female rodents made more distress calls, which were preferentially retrieved over the males by their moms.

"This study is one of the first to report a sex difference in the expression of a language-associated protein in humans or animals," researcher Margaret McCarthy, from the University of Maryland School of Medicine, said in a statement.

"The findings raise the possibility that sex differences in brain and behavior are more pervasive and established earlier than previously appreciated."

McCarthy and her colleagues also carried out a preliminary study of Foxp2 protein in a small group of children. Unlike the rats, human girls had higher levels of the protein Foxp2 in the cortex (a brain region associated with language) than boys. This could explain why human girls are the communicative sex, while the opposite sex is more vocal in rats.

The findings of the study are published in the journal Neuroscience.