Early language development and its neural correlates

Most children master the basic structures of their native language by the age of four, together with an array of cognitive and social accomplishments that appear to be necessary for language learning to take place. As a result of all this rapid development, the 4-year-old is a very sophisticated being: indeed, we have met children as young as three who can use their new linguistic tools to engage in dialogues about life after death, and the existence or nonexistence of God. How does all this happen in such a short time, in all normal children, in every culture? It is difficult to escape the conclusion that language is part of our biological heritage, an achievement that depends upon the unique characteristics of the human brain. To the extent that this is true, developmental psychology and cognitive neuroscience are faced with a great opportunity: by studying the codevelopment of brain and language in the first few years of life, we may be able to identify some of the neural mechanisms that permit the emergence of language in our species. Unfortunately, this is easier said than done. There is a discouraging disparity between our knowledge of language development and our knowledge of the brain mechanisms that support it in humans, a disparity so great that it is difficult to formulate a coherent theory of the neural events that make language possible. In fact, as we will point out later, current evidence suggests that the relationship between brain and language development is far more complex than previously believed, with causation running in both directions—including effects of learning itself on the developing nervous system. On the behavioral side, a vast and detailed body of information about language acquisition has been gathered in the 40 years since Roger Brown and his contemporaries launched modern research in this field (Kessel, 1988). This includes information from dozens of differ-