Aims: To investigate the influence of dopaminergic medication and STN-DBS on externally paced finger tapping.
Methods: We studied rhythmic finger-tapping with tactile feedback during rhythmic auditory stimulation at rates between 1-6Hz in 12 PD-patients before and after bilateral STN-DBS surgery and in 12 controls. For each stimulation rate, tapping performance was characterized by frequency, amplitude, variability, and negative asynchrony (systematic lead of the taps before stimulus-onset). Five conditions were tested after overnight-withdrawal of anti-parkinsonian medication: DOPA OFF, DOPA ON, DBS OFF, Low-Frequency-STN-DBS (20Hz), and High-Frequency-STN-DBS (130Hz).
Results: While rhythmic finger tapping abnormalities were resistent to levodopa, High-Frequency-STN-DBS significantly improved tapping amplitude and reduced the patient’s propensity to tap at faster frequencies. The negative asynchrony was significantly larger in PD patients compared to controls under all experimental conditions. Interestingly, High-Frequency-STN-DBS increased this measure. Low-Frequency-STN-DBS did not impair the patient’s tapping performance, but significantly improved tapping amplitude.
Conclusion: A major finding of this study is that, in the presence of tactile feedback, High-Frequency-STN-DBS improved both amplitude and hastening of repetitive finger movements. This contrasts with a previous report that studied hastening patterns without tactile feedback (Stegemöller et al., Neuroscience Letters (2013)), where STN-DBS had no effects on movement rate in subjects who moved faster. Thus, sensory feedback seems to be essential for DBS effects on hastened finger movements.