Differential fine force control of the upper and lower lips.

From a review of the literature, it was hypothesized that the upper lip and lower lip are differentially controlled by separate, but interacting, neuronal connectivities. A normal data base was developed for select measures of fine force control occurring within physiologic levels presumably involved in speech production. Fine force control in the lower lip was found to be significantly more stable, and recruited at higher rates than the upper lip. Explanations are presented for the lower lip superiority on these measures and observations are made concerning the use of these rudimentary physiologic measures in studies of the dysarthrias.