[Electromyographic study of 4 lip muscles and acoustic findings in parkinsonian dysarthria].
The articulatory E.M.G. activity of lower lip muscles was investigated in 3 patients with Parkinson's disease and compared with normal subjects. Four paired muscles were recorded because of their antagonist function: 1) Orbicularis oris inferioris and depressor labii inferioris; 2) mentalis and buccinator. All patients evidenced well defined E.M.G. abnormalities. These consisted in the impairment of the functional organization of the antagonist muscles (lack of reciprocal inhibition), the existence of both a resting activity between utterances and a sustained hypertonic background activity during the utterance. This study was focused on the E.M.G. activity without concomitant observation of lip movement. Parallel oscillographic records of speech acoustic signals confirmed the characteristics of the voice of parkinsonian patients: low and uniform intensity, poor timbre, irregular speech rate and abnormalities of pitch.