Acceleration and weakness in parkinsonian dysarthria.

This report presents some of the underlying neuromuscular mechanisms of dysarthric speech production as they are manifested in selected individuals with parkinsonism. Earlier explanations of parkinsonian dysarthria emphasized that the balanced hypertonus of rigidity formed the basis of reduced range of movements in speech. The present data reveal two problems in the neuromuscular control signals that can result in a reduced range of speech movements in the absence of rigidity. These neuromuscular problems are described as acceleration and weakness. The implication of these findings for the evaluation and treatment of parkinsonian dysarthria is discussed.