Cortical Dynamics Underlying Interactive Language Use

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Project Summary/Abstract This project will investigate the neural mechanisms underlying utterance planning in the service of spoken interactions. We hypothesize that planning-related activity within specific cortical sites enables the rapid vocal exchanges necessary for fluent human conversation. To test this hypothesis, we will identify planning regions using electrocorticography (ECoG), a technique with sufficient temporal and spatial precision to localize neural responses in subjects engaged in both controlled interactions and unstructured conversation. In preliminary data, we found that activity within the inferior frontal gyrus (IFG; containing Broca’s region) is often tied to utterance planning. We will characterize ECoG responses by isolating both the linguistic processing and phonological output buffer (i.e., working memory) components of these responses. We will then determine the importance of planning-related activity by examining behavioral effects that result from complementary reversible cortical perturbations. In Aim 1, we will use ECoG to test our hypothesis that specific cortical sites are involved in speech-selective motor planning in both controlled interactions (i.e., a question-answer paradigm) as well as natural, ethologically-relevant conversation. In Aim 2, we will dissect utterance planning into its component parts using two different approaches: (1) a ‘command-response’ paradigm with increasing relevance to speech (as opposed to other motor acts) to determine the degree to which these responses can be characterized as linguistic processing and (2) a variable delay picture naming task to isolate the phonological output buffering component of the observed planning activity. In Aim 3, we will assess the necessity of planning-related activity for vocal interactions by measuring the behavioral deficits that occur following transient perturbations of planning regions. Direct cortical stimulation will be used to disrupt planning activity with high temporal precision. Mild focal brain surface cooling will be used as a complementary method of modulating the temporal dynamics of planning activity. From our studies, we will investigate the cortical network enabling vocal interactions to better understand the neural mechanisms underlying turn-taking with the broader goal of informing future therapeutic interventions designed to address the clinical conditions affecting human social language use.