Exploring the expressive language function of the supplementary motor area

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Project Summary The goal of this fellowship is to provide excellent multidisciplinary training in psycholinguistics, functional neuroanatomy, and intracranial neurophysiology by developing mechanistic understanding of expressive language function in the multiple regions in the medial frontal wall, specifically the supplementary motor area (SMA) and preSMA. Dysfunction in these regions has been tied to a variety of motor and language deficits including issues with motor initiation and sequencing, articulation, and sentence planning as well as speech disorders including developmental stuttering. The SMA has been studied with respect to vocalization in non- human primate models, but the functional role of the preSMA and SMA in language production can only be explored in humans. While there are multiple motor and speech-critical cortical areas in the medial frontal wall, this proposal hypothesizes that the preSMA and SMA have unique roles in both speech/language and motor production, with the former involved in selection of action and the latter in sequencing of action. By hypothesis, PreSMA is involved in selection of elements and sequences in language and motor functions, while SMA sequencing of speech and motor programs (e.g. articulation). While these regions interact with different subcortical and cortical regions, sequence vs. selection is a critical variable that distinguishes activation in these regions in both language and motor tasks. Critically, we hypothesize that the same regions perform selection (preSMA) and sequencing (SMA) in motor and language tasks. To answer this question, we will utilize stereo EEG (SEEG) intracranial recording in chronically-implanted epilepsy patients (N=20) in conjunction with neuropsychological testing and functional MRI. In Aim 1, we will investigate the relationship of sequencing vs. selection in motor and language tasks (repetition vs. generation of sequences of finger taps and syllables) to broadband gamma activity in the preSMA and SMA. We hypothesize that preSMA and SMA will be activated in the selection (generation) condition for both motor and language tasks, while sequencing (repetition) tasks that will activate only SMA. We will then investigate the connectivity of the preSMA/SMA to understand how language-relevant information is transferred to this region for the purposes of speech production. In Aim 2, we will first use SEEG cortico-cortical evoked potentials to show direct effective connectivity between preSMA/SMA and language regions including speech motor cortex (output), inferior frontal gyrus (phonologic selection), and posterior middle temporal gyrus (semantic selection). We will then use SEEG functional connectivity to demonstrate that functional connectivity to language regions increases during language tasks in comparison to motor tasks. The cross-disciplinary approach proposed here will tie the functional neuroanatomy of preSMA/SMA to psycholinguistic analyses of expressive language. Translated into clinical practice, our results will create a better understanding of speech disorders including stuttering, improve functional brain mapping, and elucidate the mechanisms of language dysfunction in SMA syndrome.