The New Organization of Language and the Brain
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Abstract
Language is often said to be supported by a circumscribed and static set of cortical areas, predominantly in the left hemisphere. Experimental tasks used to localize hypothetical linguistic functions in the brain, however, do not resemble our everyday experience with language. To address the open question of how the brain supports language in natural settings, I study how the brain processes more ecological stimuli (e.g., watching television). These stimuli are associated with an abundance of contextual information. I will show that there are multiple simultaneously active brain networks supporting language and that these networks dynamically re-organize themselves depending on the types of context available to listeners. Activity patterns within individual networks suggest that the motor system plays a central role in using context. Specifically, the motor system becomes active when observing speech-associated mouth movements and gestures and when expectations about forthcoming words are strong. Why does the motor system of the listener become active as if producing movements or speaking words? Through feedback, the motor system has the remarkable ability to predict the sounds and words associated with activated motor programs. These predictions then allow the brain to do less processing of incoming sensory information, freeing up neural resources for other purposes. Thus, the neurobiology of language involves a top-down mechanism that makes use of different contexts in different networks distributed throughout the whole brain. This suggests that we should revise contemporary views of language as bottom-up, context insensitive, and occurring in a small set of functionally fixed cortical areas.