Labial kinematics during speech in patients with parkinsonian rigidity

Studies of orofacial motor control in Parkinson's disease (PD) have demonstrated that these subjects may exhibit hypokinesia and bradykinesia, as well as increased muscle tone. Yet the relationship between aberrations of orofacial movement and muscle rigidity remains unclear. Measures of labial muscle rigidity and movement were made for 12 parkinsonian and 9 age-matched control subjects. Displacement amplitude, peak instantaneous velocity, and movement time were evaluated during repetitive syllable productions. The results showed that while mean parkinsonian displacement amplitudes and velocities were lower than the normal control subjects, there was no statistical relationship between labial rigidity and the degree of movement abnormality. It is concluded that while rigidity may play a part in the overall disability, it does not sufficiently explain the labial articulatory difficulties associated with parkinsonism. This is in agreement with the literature on limb rigidity and movement aberrations in PD, suggesting that rigidity and bradykinesia may represent independent pathophysiological phenomena.