Decoding speech intent from non-frontal cortical areas.

Brain-machine interfaces (BMIs) have advanced greatly in decoding speech signals originating from the speech motor cortices. Primarily, these BMIs target individuals with intact speech motor cortices but who are paralyzed by disrupted connections between frontal cortices and their articulators due to brainstem stroke or motor neuron diseases such as amyotrophic lateral sclerosis. A few studies have shown some information outside the speech motor cortices, such as in parietal and temporal lobes, that also may be useful for BMIs. The ability to use information from outside the frontal lobes could be useful not only for people with locked-in syndrome but also to people with frontal lobe damage, which can cause nonfluent aphasia or apraxia of speech. However, temporal and parietal lobes are predominantly involved in perceptive speech processing and comprehension. Therefore, to be able to use signals from these areas in a speech BMI, it is important to ascertain that they are related to production. Here, using intracranial recordings, we sought evidence for whether, when and where neural information related to speech intention could be found in the temporal and parietal cortices. Causal information enabled us to distinguish speech intent from resting state and other processes involved in language processing or working memory. Information related to speech intent was distributed widely across the temporal and parietal lobes, including superior temporal, medial temporal, angular, and supramarginal gyri. This provides evidence of a decodable production-related signal in these areas. This insight may help in designing speech brain-machine interfaces that could benefit people with locked-in syndrome, aphasia or apraxia of speech.