Electrophysiological Approaches to Understanding Functional Organization of Speech in the Brain

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ABSTRACT FROM PARENT R01 To understand speech, the human brain must parse and transform a noisy acoustic signal into meaningful linguistic content, including phonemes, syllables, words, and sentences. This involves determining the timing of important acoustic events, such as the onset of a sentence or a phrase. Following detection of these onsets, the content of the sentence must be determined. The posterior superior temporal gyrus (pSTG)—including the classic “Wernicke’s area”—is critical to this process, but until recently, little was known about its functional organization, and in particular how this functional organization changes throughout development. Our recent work showed that a spatially discrete region of the pSTG is critical for indicating when a sentence or phrase begins. This region is distinct spatially and functionally from more anterior “sustained” areas that encode phonetic feature information throughout a sentence. Functionally, both posterior onset and anterior sustained regions show short and long temporal integration times, respectively, suggesting complimentary roles in natural speech processing. Here, we propose an innovative approach using rare datasets where neural activity is recorded directly from the human auditory cortex and speech-related areas in pediatric patient participants undergoing clinical evaluation for epilepsy surgery. This method overcomes the spatial and temporal resolution limitations of other noninvasive procedures, and provides a rare window into the function of the human auditory cortex. The proposed study will use high resolution intracranial recordings to investigate how the brain detects acoustic onsets in natural speech sound mixtures, and how neurophysiological responses to these sounds change from early childhood to adolescence. Furthermore, we will investigate how these responses to onsets are modulated by context, including during attention and for self-generated sounds. In addition to providing insight into the basic functional organization of the human auditory cortex and cortical mechanisms for auditory scene analysis, this research has important implications for the development of a speech brain computer interface. Our results could also inform how speech and language are processed in natural contexts, which has implications for the treatment of developmental language disorders, auditory processing disorder, dyslexia, autism, and aphasia.