Speech freezing in Parkinson's disease: a kinematic analysis of orofacial movements by means of electromagnetic articulography.

Kinematic recordings of orofacial movements by means of electromagnetic articulography were performed in an akinetic-rigid Parkinsonian patient presenting with intermittent speech freezing in diadochokinesis tasks (rapid repetitions of the syllable /ta/). During freezing periods the patient produced a sustained /a/ instead of the required consonant-vowel sequences. The underlying articulatory trajectories were characterized by repetition rates amounting to 8-10 Hz concomitant with reduced movement amplitudes. Obviously, the undershooting of articulatory gestures failed to establish a sufficient occlusion of the vocal tract giving rise to the perceived speech freezing. In contrast, preserved diadochokinesis occurred at frequencies of 4-6 Hz. Most probably, the increased articulatory repetition rate reflects a pacing of orofacial movements by released tremor oscillations. Due to slowing of articulatory movements spastic dysarthrics can also present with missing syllabic modulation during oral diadochokinesis. The results of the articulographic recordings demonstrate the different pathophysiology of Parkinsonian freezing.