Short-Term Effects of Repetitive Transcranial Magnetic Stimulation on Speech and Voice in Individuals with Parkinson’s Disease

Abstract

The main characteristics of dysarthria in Parkinson’s disease (PD) are monotony of pitch and loudness, reduced stress, variable speech rate, imprecise consonants, and breathy and harsh voice. Earlier treatment studies have shown that dysarthria is less responsive to both pharmacological and surgical treatments than other gross motor symptoms. Recent findings have suggested that repetitive transcranial magnetic stimulation (rTMS) may have a beneficial effect on vocal function in PD. In the present study, 10 individuals with mild PD and no or minimal dysarthria were treated with rTMS as well as placebo stimulation in a blinded experiment. Stimulation was delivered using a frequency of 10 Hz and a stimulation intensity of 90% of the motor threshold. The site of stimulation was the cortical area corresponding to the hand, on the hemisphere contralateral to the patient’s most affected side. The participants were audio-recorded before and after both rTMS and sham stimulation. Acoustic analysis was performed on 3 sustained /a:/ for each of the 4 conditions, and analyzed both for the whole group as well as for men and women separately. Results showed that there were no significant differences between any of the conditions regarding duration of sustained fricative or sustained vowel phonation, diadochokinetic rates or intelligibility. Above all, the results of acoustic analyses showed an effect of placebo; there was a significant reduction in fundamental frequency (F₀) variation, pitch period perturbation, amplitude period perturbation, noise-to-harmonics ratio and coefficient of variation in F₀ between the recordings performed before compared to after sham stimulation.