Neural representations of speech production in neocortical and cerebellar regions

Abstract

Speech production requires the coordinated control of the supralaryngeal articulators (e.g., the lips, tongue, and soft palate) together with laryngeal control of phonation. While cortical sensorimotor regions are known to encode phonetic features, how the cerebellum represents speech and how cerebellar representations integrate within cortico-cerebellar circuits remain poorly understood. Using 7T functional MRI and representational similarity analysis, we examined neural representations of speech production during overt syllable production varying in place of articulation and voice onset time. We found reliable, syllable-specific activity patterns across both cortical and cerebellar speech regions. Ventral primary sensorimotor cortex distinguished syllables by place of articulation, whereas dorsal sensorimotor cortex showed sensitivity to voice onset time, consistent with a functional dissociation between articulatory and phonatory control. We also found secondary speech areas that encoded phonetic features. Specifically, the parietal operculum showed sensitivity to both place of articulation and voice onset time, positioning it as an integrative node within the speech motor network. In the cerebellum we found superior and inferior speech areas, which did not differ in their representational geometry. Surprisingly, the cerebellar syllable representations were most similar to those found in the parietal operculum rather than in primary motor cortex, with both regions encoding both phonetic features. These findings indicate that cerebellar speech representations are not solely determined by a single primary sensorimotor area but instead align more closely with the representations in the parietal operculum, suggesting that cerebellar speech areas contribute to the coordination of phonation and articulation.