Effect of L-dopa on speech in Parkinsonism. An EMG study of labial articulatory function.

The articulatory function of the labial musculature has been investigated electromyographically before and after treatment with l-dopa in patients with Parkinsonism who had dysarthria. Before medication the EMG traces generally showed a constant, abnormally increased, tonic activity, together with disturbed reciprocal innervation, which impaired the articulatory activity. After medication the tonic hyperactivity was reduced and the reciprocal innervation re-established. This normalization of the EMG articulatory pattern was paralleled by an improvement of the dysarthria.