312 Stimulus-Response Correlation Analysis Dissociates Spatiotemporal Cortical Networks Supporting Speech Production

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INTRODUCTION: Understanding the spatiotemporal distribution of cortical activation during language production is a central question in cognitive neuroscience with broad clinical applications. High spatial/temporal resolution recording over multiple brain regions can help resolve this question. To interpret this electrophysiological data, specific psycholinguistic manipulations with testable behavioral predictions are necessary. METHODS: Subjects (20 healthy, 15 SEEG) are presented visual stimuli (pictures, words, pseudowords) to name but are instructed to delay response until a go cue at 0/400/1000 ms. Exploiting the temporal variance induced by delay, we calculate stimulus/response-locked correlation of high gamma (70-200 Hz) activity at each contact. We parcellate cortical networks in time and space by shifts in stimulus-response correlation space and compare these shifts to variance in RT to validate this approach. RESULTS: Behaviorally, the factor delay modulated the effect of lexical selection on RT (p = 0.021) but did not modulate the effect of phonological planning (p = 0.4), confirming the paradigm separates processing stages. Stimulus-response correlation analyses revealed globally-invariant structure across subjects. Certain regions showed strong stimulus-locking (occipital lobe) or response-locking (motor cortex), but most regions were intermediate. Shifts in correlation space identified dissociated networks that predicted substantial variance in RT in lexical selection (R2 = 0.64) and phonological density (R2 = 0.75). Using a leave-one-subject-out cross validation approach, these shifts explained 31.4% of variance in RT at the trial level. We find that there are sequential but overlapping stages of speech production widely distributed across the cortex. CONCLUSIONS: Stimulus-response correlation space reveals stable spatiotemporal signatures of psycholinguistic processing that generalize across individuals, consisting of a mixed serial and overlapping process of speech production. This approach also provides a functional space in which electrophysiological data from multiple subjects, each with different electrode coverage, can be directly compared.

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