Sensory trick in musician's dystonia: the role of altered sensory feedback in pianist's dystonia

Dystonia in pianists belongs to a group of dystonic movement disorders termed focal dystonias. It is characterized by the degradation of voluntary control of highly skilled movement patterns involved in piano playing. Previous studies have shown that apart from being a movement disorder, many forms of focal dystonias involve several sensory abnormalities, and cutaneous stimuli may temporarily reduce the severity of motor symptoms in patients. The stimulus that may successfully reduce motor symptoms is termed sensory trick. Studies on cutaneous sensory trick of focal neck dystonia suggested that sensory tricks should be regarded as a complex dynamic mechanism that corrects the perceptual dysbalance of the abnormal motor output. The motivation for this dissertation came from anecdotal reports of organ players suffering from musician’s dystonia who reported a significant reduction of the motor symptoms when playing on a pipe organ with delayed sound production after the key stroke due to mechanical coupling of the keyboard and the organ pipes. The aim of the dissertation is to investigate the possible underlying mechanism of these anecdotal reports by using altered sensory feedback in both auditory and sensory modalities. The dissertation is divided into 2 parts: The first part of the dissertation is based on behavioural studies of the effect of altered auditory feedback in musician's dystonia (MD) and discusses whether altered auditory feedback (AAF) can be considered as a sensory trick in MD. Furthermore, the effect of AAF is compared with altered tactile feedback, which can serve as a sensory trick in several other forms of focal dystonia. The results of the studies suggest that in the context of our experimental designs, AAF and altered tactile feedback did not have a beneficial role in motor coordination in MD patients. We propose that altered auditory and tactile feedback do not serve as effective sensory tricks and may not temporarily reduce the symptoms of patients suffering from MD in this experimental context. The second part of the dissertation continued with manipulating different sensory feedbacks in the piano playing of healthy pianists and pianists suffering from MD. This study investigated the impaired cortical functional network of pianists who suffer from MD by employing altered auditory and altered tactile feedback during scale playing with multichannel electroencephalography (EEG). By comparing the two groups under different sensory feedback, the EEG data suggested a trend of higher degree of inter-regional phase synchronisation between the frontal and parietal regions and between the temporal and central regions in pianists suffering from MD in conditions that are relevant to the long-trained auditory-motor coupling (normal auditory feedback and complete deprivation of auditory feedback), but such abnormalities are decreased in conditions with delayed auditory feedback and altered tactile feedback. These findings support the hypothesis that the impaired sensorimotor integration of MD patients is specific to the type of overtrained task that the patients were trained for and can be modified with altered sensory feedback. In conclusion, the results of the studies included in this dissertation showed that under our experimental conditions, AAF cannot serve as a successful sensory trick in MD. Nevertheless, both altered auditory and tactile feedback can induce different alternations to the long-range inter-regional neural synchrony in MD patients and this may have an implication for the task-specific deficit of inhibition in MD.