Brain mechanisms of speech and language
How do we understand speech so quickly and without errors? The contemporary theories suggest that the understanding of a word requires activation of a large distributed network – the same network that has been activated when the word has been learned. The child learns the first verbs at the moment when he or she performs the action itself, and when the adults name this action. Therefore, it is likely that to understand the meaning of the word "throw", we need to activate a distributed network that includes auditory areas that process the sounding word, as well as the motor cortex, through which the respective movement is realized. To test this hypothesis, we used verbs that describe actions of different parts of the body: arms, legs, mouth, and observed how the motor cortex changed its activity while the subject listened to these words. Our results for the first time demonstrated reliable body-part-specific activation in the motor cortex. Indeed, the cortical area of the motor representation of the hand was activated in response to the word that described the action of the hand, while the words that described actions of the leg and the mouth activated cortical representations of the leg and the mouth, respectively. This data expands our knowledge on how words are stored in the brain and what the process of "understanding" a word is. They show that extensive distributed networks are re-activated, referring to the context in which the word was initially learned. The results of our study were recently published in Proceedings of the National Academy of Sciences of the United States of America. These results raise new questions. Is this activation of the motor cortex a sign of early semantics, or does it simply reflect the word categorization? In our future studies, we will try to answer these questions.
This research is conducted in cooperation with Professor Yu.Yu. Shtyrov, Center for Neuroeconomics and Cognitive Research, National Research University "Higher School of Economics", Moscow, Russia and Department of Clinical Medicine, Center for Functionally Integrative Neuroscience (CFIN), Aarhus University, Aarhus, Denmark.