Fine force and position control of select orofacial structures in the upper motor neuron syndrome.

A fundamental pathophysiologic feature of patients with the upper motor neuron syndrome is a reduction in the rate of force change associated with generating fine levels of force in the upper lip, lower lip, tongue, and jaw. These measures were highly related to impairments in movement velocity in these same structures. End point accuracy, defined as the ability to generate specified target levels for both force and position, was relatively well preserved in these structures. Moreover, these measures of dynamics in select structures of the oral motor system were found to be highly related to impairments in speech intelligibility. Quantitative physiologic measures of force and movement control are considerably more sensitive than conventional methods in determining the distribution and nature of orofacial motor impairments which degrade fine motor performance.