2-year-olds don't talk in sentences but can still tell nouns from verbs: new brain study suggests that toddlers know basic grammar.

Two-year-olds know more about grammar than they can say. Budding toddlers recognize the difference between nouns and verbs in simple sentences, even though the kids don't utter such sentences for at least another year, say Anne Christophe of the Laboratory of Cognitive Sciences and Psycholinguistics in Paris and her colleagues.

Children begin to use two or more words at a time by age 2, but their statements are typically incomplete and show no signs of grammatical knowledge. Yet upon hearing a sentence in which a noun incorrectly replaces a verb, or a verb incorrectly replaces a noun, toddlers display split-second brain responses that signal awareness of the rule violations, Christophe's team reports online June 29 in Developmental Science.

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Electrical activity, mainly relegated to the left-frontal brain, spiked when toddlers heard nouns in a verb position. Electrical responses farther back on the brain's left side, in the temporal lobe, jumped as toddlers heard verbs in a noun position. Both patterns resembled those that have already been implicated in noun and verb knowledge in adults.

"This experiment suggests that brain networks responsible for language processing get organized extremely early, showing striking similarities with the adult system long before children start producing adult-like language," Christophe says. A basic grasp of native-language rules may assist youngsters in learning the meanings of new words and other elements of language, she says.

In contrast, some scientists suspect that toddlers memorize a large repertoire of verbal phrases before making generalizations about object and action words at around age 3. A related hypothesis holds that language learning depends partly on a quantitative ability to notice features of speech that regularly go together.

"Children could well have some basic syntactic knowledge by age 2, which continues to develop throughout early childhood as they identify the statistical regularities of their language," remarks psychologist Erik Thiessen of Carnegie Mellon University in Pittsburgh.