Sentence-level neural dynamics in speech motor cortex

Prior recordings from speech motor cortex have revealed phonemic, syllabic, articulatory and speech-sequence representations, while more recent studies indicate that activity may also reflect higher-order features of speech production. However, whether speech motor cortex is sensitive to the linguistic organization of sentences remains unclear. Here we show that single-unit activity in speech motor cortex contains information about sentence-level linguistic structure. In three BrainGate2 participants with implanted microelectrode arrays in the left precentral gyrus, we recorded neural activity during an instructed-delay speech task comprising English sentences, word lists, syntactically structured nonword sentences and nonword lists. Neural activity in areas 6v and 55b contained speech- and language-related components, with stronger stimulus-condition effects in 55b, and stimulus condition was decodable in all three participants. In two larger datasets, semantic categories of English sentences were decodable from neural activity. These findings demonstrate that speech motor cortex encodes information about linguistic structure and semantic content at the level of sentences.