The reduction of tonal range and of average pitch during speech production in off parkinsonians are restored by L-DOPA

Résumé En

The dysprosody of Parkinsonian’s disease (PD) has been partly interpreted as a disorder affecting the variation of fundamental frequency (F0), the monotonous intonation of speech being the consequence of the tonal range reduction. To date, some controversial results have been reported concerning the average pitch which has been found either increased or comparable to that of control subjects (see Gentil et al., Rev. Neurol., 1995, 151: 105-112). However in most of these studies, the pharmacological status of the patients was not systematically controlled.The aim of this study was to analyse the F0 during speech production in a more exhaustive manner by sampling the signal at every 10 ms interval over the entire reading of a text. The tonal and dynamic properties of the frequency distribution were assessed by measuring the average voice pitch, the limits and the dynamics of tonal variations. 10 male PD patients were tested during "off " state and after L-DOPA treatment; they were compared with an age-matched group of 10 male control subjects.The results showed that comparing to normals the voice intonation of PD patients during "off" state is caracterised by a significant reduction of the tonal dynamics of F0 and by a significant lowering of the average and the maximum limit of voice pitch. In these patients, the L-DOPA treatment significantly increased the tonal dynamics, the average and the maximum limit of voice pitch, so that no significant difference was observed between treated patients and control subjects.