Michael Grossbach

Defective Inhibition and Inter-Regional Phase Synchronization in Pianists With Musician's Dystonia: An EEG Study

Recent neurophysiological studies have associated focal‐task specific dystonia (FTSD) with impaired inhibitory function. However, it remains unknown whether FTSD also affects the inhibition (INH) of long‐term overlearned motor programs. Consequently, we investigated in a Go/NoGo paradigm the neural correlates associated with the activation (ACT) and inhibition of long‐term overlearned motor memory traces in pianists with musicians dystonia (MD), a form of FTSD, during a relevant motor task under constraint timing conditions with multichannel EEG. In NoGo trials, the movement related cortical potentials showed a positive shift after the NoGo signal related to inhibition and was significantly smaller over sensorimotor areas in musicians with MD. Further, we observed an increase at 850–900 ms in the power of beta oscillations which was significantly weaker for the patient group. The role of the inter‐electrode phase coupling in the sensorimotor integration of inhibitory processes turned out to be the most relevant physiological marker: the global phase synchronization during INH exhibited an increase between 230 and 330 ms and 7–8 Hz, increase which was significantly smaller for pianists with MD. This effect was due to a weaker phase synchronization between the supplementary motor cortex and left premotor and sensorimotor electrodes in patients. Thus, our findings support the hypothesis of a deficient phase coupling between the neuronal assemblies required to inhibit motor memory traces in patients with MD. EMG recorded from the right flexor pollicis longus muscle confirmed that patients with MD had a disrupted INH in NoGo trials. Hum Brain Mapp 2009.

Musician's dystonia is highly task specific: no strong evidence for everyday fine motor deficits in patients.

OBJECTIVES 1) To examine the fine motor skills used everyday by patients suffering from musicians dystonia (MD) in the upper limb in order to verify whether MD is task-specific; and 2) to compare the affected and non-affected hands of MD musicians vs healthy musicians in performance of these tasks in order to clarify whether dystonic symptoms can be found in the non-affected side of MD patients. BACKGROUND MD is typically considered to be focal and task specific, but patients often report impairment in everyday life activities. Furthermore, in the course of MD, about 15% of patients complain of dystonic symptoms in other parts of the body. METHODS Twenty-seven musicians affected by MD and 27 healthy musicians were studied using 1) the Motor Performance Test Series, 2) a kinematic analysis of handwriting, and 3) an assessment of the grip force regulation while lifting and moving a manipulandum. RESULTS Patients performed most fine motor tasks without any evidence of a deficit. Exclusively in the handwriting tasks (2), they exhibited fewer frequencies of the written trace and a prolonged overall writing time. CONCLUSION MD is highly task specific and does not strongly affect other motor skills. The subtle deficits in handwriting may be explained as a consequence of a general psychological disposition rather than as compensatory mechanisms to avoid the appearance of dystonic symptoms. Furthermore, we did not find signs of multifocal motor deficits in the unaffected hands of MD patients.

Pathophysiology of writer’s cramp: an exploratory study on task-specificity and non-motor symptoms using an extended fine-motor testing battery

BackgroundWriter’s cramp (WC) is a task-specific focal dystonia which manifests itself as abnormal postures interfering with motor performance. As the spread of motor symptoms remains controversial and non-motor symptoms are widely discussed, in this exploratory study, we explore the pathophysiology of WC, focusing on task-specificity and the psychological profiles of WC patients.MethodsIn 14 right-handed WC patients and matched controls, we assessed motor control by applying motor performance tests (Vienna Test Series), as well as using writing analysis and grip-force measurements. Moreover, detailed psychological factors were assessed. Classification trees were used to distinguish patients from controls.ResultsThe total duration of writing and the vertical writing frequency of the pen are the most important variables to split the data set successfully into patients and controls. No other variables concerning motor performance tests, grip-force measurements or psychological factors correctly separated patients and controls.ConclusionsOnly variables from the writing tasks successfully separated patients and controls, indicating a strong task-specificity of WC in our patient group. Future research should be performed with larger samples of untreated WC patients in early stages of impairment, without any secondary motor disturbances, to verify our findings.