Effects of levodopa and deep brain stimulation on motor speech performance in Parkinson’s disease

BackgroundAbnormalities in motor speech performance are frequently observed in Parkinson’s disease and are thought to be induced by complex dysfunction of planning, preparing and execution of speech motor sequences. The aim of our study was to test the differential influence of levodopa and bilateral deep brain stimulation of the subthalamic nucleus in Parkinsonian patients based upon a multi-level syllable repetition paradigm.MethodsTwenty-four patients and 32 healthy subjects were tested. Patients had to perform the speech task under three different conditions: OFF-Stimulation/OFF-Medication, ON-stimulation OFF-Medication and ON-Stimulation/ON-Medication. Participants had to repeat a single syllable (/pa/) or a pair of alternating syllables (/pa-ti/) in a self chosen isochronous pace or in a given pace of 80 per minute. Percental coefficient of variance of interval length was measured for description of pace stability throughout the performance.ResultsCoefficient of variance in the patient group was elevated in the tasks consisting of a single syllable repetition and showed a further increase in the alternating syllable tasks. Deep brain stimulation led to a further deterioration whereas levodopa induced an amelioration of coefficient of variance significantly in the more complex task consisting of the repetition of alternating syllables.ConclusionsIn the patient group, pace performance was observed to be irregular in all tasks, but showed a further decline under deep brain stimulation and when two or more equal demands (steadily keeping a given pace/alternating syllables) were present as a possible hint for additional executive dysfunction which was partially compensated by levodopa.