Peter Stein1, Elliot Saltzman1,2, Kenneth Holt1,3, Dagmar Sternad4. 1. College of Health and Rehabilitation Sciences, Boston University, Boston, Massachusetts, USA. 2. Haskins Laboratories, New Haven, Connecticut, USA. 3. Wyss Institute for Biologically Inspired Engineering at Harvard University, Boston, Massachusetts, USA. 4. Departments of Biology, Electrical and Computer Engineering, and Physics, Northeastern University, Boston, Massachusetts, USA.
Abstract
INTRODUCTION: Task-specific focal dystonia (TSFD) is a disorder marked by degraded coordination in complex and exacting psychomotor tasks, such as musical performance. Its development is associated with prolonged and intensive practice of these tasks, but the etiology of TSFD is still unknown. The prevailing hypothesis was informed by findings in primates following repetitive simple grasping actions. This model implies, however, that complex manual tasks that yield more intricate and subtly varying sensorimotor patterns, as found in musical performance and handwriting, should be unlikely to lead to focal dystonia. HYPOTHESIS: We propose an alternative, "predictive-control" etiological hypothesis: When an overtaxed performer exhibits poorly controlled variability and errors in motor execution of a well-learned, high-precision task, predictive control processes deteriorate. This includes, in particular, those related to the formation or updating of a forward dynamic model that maps motor commands to predicted end-effector state, e.g. position and velocity of a key-pressing digit. CONCLUSION: Based on a critical literature review we argue that this results in the characteristic signs of focal dystonia, such as freezing, halting and inappropriate co-contraction specific to the task. Directions for future research are briefly discussed.
INTRODUCTION: Task-specific focal dystonia (TSFD) is a disorder marked by degraded coordination in complex and exacting psychomotor tasks, such as musical performance. Its development is associated with prolonged and intensive practice of these tasks, but the etiology of TSFD is still unknown. The prevailing hypothesis was informed by findings in primates following repetitive simple grasping actions. This model implies, however, that complex manual tasks that yield more intricate and subtly varying sensorimotor patterns, as found in musical performance and handwriting, should be unlikely to lead to focal dystonia. HYPOTHESIS: We propose an alternative, "predictive-control" etiological hypothesis: When an overtaxed performer exhibits poorly controlled variability and errors in motor execution of a well-learned, high-precision task, predictive control processes deteriorate. This includes, in particular, those related to the formation or updating of a forward dynamic model that maps motor commands to predicted end-effector state, e.g. position and velocity of a key-pressing digit. CONCLUSION: Based on a critical literature review we argue that this results in the characteristic signs of focal dystonia, such as freezing, halting and inappropriate co-contraction specific to the task. Directions for future research are briefly discussed.