Quantitative assessment of rest and action tremor and the effect of cueing in Parkinson’s disease patients treated with deep brain stimulation

Introduction: In Parkinson’s disease rest and action tremor may occur. High frequency deep brain stimulation in basal ganglia nuclei has proved to be effective in the suppression of tremor. In addition, rhythmic auditory cues have shown to result in improved performance of repetitive movements, possibly by suppressing action tremor. The aim of this study was to investigate if electrical stimulation has similar effects on rest and action tremor, and whether in case of action tremor, the effect of electrical stimulation is similar to or enhanced by auditory cueing.

Methods: Three exercises were carried out by 7 Parkinson’s disease patients treated with deep brain stimulation of the subthalamic nucleus: 1) sitting at rest; 2) performing a hand tapping movement as fast as possible; 3) performing hand movements on the rhythm of an auditory cueing signal. Inertial sensors registered the movement of the hands during the tests. The exercises were repeated for four different stimulation settings.

Results: Electrical stimulation may either enhance or suppress rest and/or action tremor. Power spectral density analysis shows that tremor suppression is accompanied by an increase in relative power in the low frequency band for both rest and action tremor. Most patients could (temporarily) phase lock their hand movements to the cueing signal of 1.6 Hz. Cueing signals at higher frequencies (3.2 and 4.8 Hz) could result in (n:m) phase locking of tremor as well as movement.

Conclusion: Electrical stimulation results in a re-scaling of tremor, while auditory cueing may enhance suppression.