Boys and girls tend to use different parts of their brain to learn some fundamental parts of grammar, according to a new U.S. study on Tuesday.

"Sex has been virtually ignored in studies of the learning, representation, processing and neural bases of language," said lead author Michael Ullman, a neuroscientist at Georgetown University. "This study shows that differences between males and females may be an important factor in these cognitive processes."     

Men and women may process words differently because of different levels of the hormone estrogen, which is much higher in females and affects brain processing, according to Ullman.　

For the study, published in Developmental Science, researchers investigated the different brain systems that children used when they made mistakes like "Yesterday I holded the bunny." They found that girls tended to use a process that dealt with memorizing words and associations between them, whereas boys used a process governing the rules of language.

For this study, Ullman and his colleagues studied how a group of 10 boys and 15 girls, between the ages of two and five, used regular and irregular past-tense forms of verbs.

Children would be likely to make mistakes like "holded," as those errors result from children applying the "add-ed" rule of regular verbs when they can't remember the form of the irregular verb.

The results of the study showed: Girls used "holded" far more than boys. Digging deeper, the researchers found that words liked "holded" had many rhyming verbs with regular past-tense forms, like folded and molded.     

According to the researchers, the girls were using their declarative memory to memorize the regular past tense forms and then applying those forms to rhyming irregular verbs.

Declarative memory referrs to a "mental lexicon" in memorizing and remembering words, Ullman explained.　

"This memory is not just a rote list of words, but underlies common patterns between words, and can be used to generalize these patterns," Ullman said.     

But for boys, there was no association between the number of rhyming regular past-tense verbs and the verbs that were used incorrectly. According to Ullman, this suggests that boys were using their procedural memory that contains the rule to add "–ed" to create past tense verbs. 　

Procedural memory, controlled by a different part of the brain, is used to combine words in sentences, Ullman gave the explanation.