Abstract
Human speech production requires fine neural control of the articulators and the larynx during vocalization. The representation of the larynx in the human brain is debated. Vocalizations can be elicited by stimulation of the ventral motor cortex, but neuroimaging reveals that producing vocalizations evokes activity in both a dorsal and a ventral area. We designed an fMRI study to isolate brain activity related to laryngeal activity during vocalization while controlling for breathing. We mapped the cortical motor representation of the larynx during vocalization and dissociated it from representations of supralaryngeal articulators (the lips and tongue). We also mapped the hand representation in the left hemisphere. Furthermore, we characterized the microstructure of activated cortical regions using structural and quantitative neuroimaging in individual subjects. We found two separate activations during vocalization, which are in anatomically distinct parts of the brain. Individual subjects show a consistent somatotopic arrangement of the movement-related activations. Quantifications of cortical microstructure suggest that the dorsal, but not the ventral larynx area, is located in primary motor cortex as indexed by high myelin content and thicker cortex. It remains unclear, however, whether and how these two brain areas differentially contribute to laryngeal motor control.
