Lip Muscle Function in Parkinsonian Dysarthria

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Abstract
The articulatory EMG activity of lip muscles was investigated in patients with Parkinsonism and dysarthria and compared with normal-speakers. Furthermore, the effect of L-Dopa treatment on the dysarthric EMG activity was evaluated. Although articulatory ability unproved in the experimental situation, it was possible to recognize reproducible abnormalities of the EMG pattern common to all patients. The resting activity between utterances was markedly increased and often progressed to a sustained hypertonic background activity, particularly in M. lev. lab. and M. dep. lab., as a sign of an exaggerated speech posture during the utterance. The functional organization of the lip muscles into two antagonistic groups for contrasting speech gesture movements was impaired. There were no signs of reciprocal inhibition. There was an obvious relationship between this disturbed activity pattern and the misarticulation of labial stop consonants. Furthermore, a longer anticipation period and a lack of context dependence of the EMG activity were often observed. L-Dopa medication was followed by a reduction of background activity and a reestablishment of reciprocal activation. These findings are discussed in relation to available data on limb muscle function in Parkinsonism.