Inclusion Criteria:  Chronic deep brain stimulation (> 1 year) in the internal globus pallidus in patients with isolated dystonia. Deep brain stimulation settings and dystonia medication stable for > 3 months. Understanding about and consent to the study and signed informed consent form.  Exclusion Criteria:  Relevant comorbidities that might interfere with study endpoints (esp. palliative disease and severe neurologic or psychiatric comorbidities).