Sub-movement cueing and motor sequence execution in patients with Huntingtonʹs disease

Objectives: We investigated whether the type of sub-movement cueing during the execution of motor sequences influences the movement time in patients with Huntingtonʹs disease. Methods: The kinematic variables of rapid sequential free arm movements executed with different types of sub-movement cueing – externally-triggered (ET) and self-initiated (SI) tasks – were analyzed in 7 patients and 7 healthy controls. The ET task required subjects to initiate movements in response to consecutive visual go signals; the SI task allowed them to start at will. Results: HD patients performed ET and SI tasks slower than normal subjects. Both groups executed ET sequences slower than SI, but movement times for the two tasks differed less in patients than in controls. Patients paused normally between sub-movements during the SI task, but they had slower reaction times for all the sub-movements of the ET task. Conclusions: Slower execution of both motor tasks indicates that HD patients are bradykinetic in performing sequential free arm movements. Our finding that total movement times for SI and ET tasks differ less in patients than in controls suggests that HD impairs internal more than external cueing mechanisms