April 2013

Human speech critically depends on the ability to produce the large number of sounds that compose a given language. The wide range of spoken sounds results from highly flexible configurations of the vocal tract, which filters sound produced at the larynx through movements of the lips, jaw and tongue that need to be precisely coordinated to produce intelligible speech. This behavior is known to require orchestration from the ventral half of the lateral sensorimotor (Rolandic) cortex (ventral sensorimotor cortex, vSMC), but the mechanisms by which this occurs are essentially unknown. Bouchard and colleagues addressed this question by recording neural activity directly from the cortical surface in three human subjects implanted with high-density multi-electrode arrays as part of their preparation for epilepsy surgery. Intracranial cortical recordings were synchronized with microphone recordings as subjects read aloud consonant-vowel syllables that are commonly used in American English. The recordings revealed distinctive cortical representations, organized somatotopically, in the vSMC for each of the four primary articulators: the lips, jaw, tongue and larynx. Observations of the population-derived patterns of activation during speech production showed these representations were coordinated temporally as sequences during syllable production. Spatial patterns of cortical activity showed an emergent, population-level representation, which was organized by phonetic features. Over tens of milliseconds, the spatial patterns transitioned between distinct representations for different consonants and vowels. These results reveal the dynamic organization of the speech sensorimotor cortex during the generation of multi-articulator movements, and that a relatively small set of articulator representations can combine flexibly to create the large variety of sounds associated with human speech (Nature 2013;doi:10.1038/nature11911).