Previous studies have not yielded consistent results on the role of PAC strength during movement in patients with PD with some studies reporting enhanced (13, 15) and at least one other study reporting normal movement-related PAC (14). However, interpretation of these results was hampered by insufficient information about the actual movement performed during the EEG recording. In particular, it remained unclear whether the characteristics of the movements reflected Parkinsonian abnormalities. Our study attempted to address this ambiguity by investigating PAC dynamically and relating its magnitude and modulation to the characteristics of concomitantly performed self-paced repetitive movements. The motor impairment of patients with PD was evident in the reduced EMG slope in the slow tapping task, the lower movement rate in the fast tapping task, and the amplitude decrement during both slow and fast tapping. This is consistent with previous reports (24, 29, 37). However, as assessed by the movement rate and EMG slope, the behavioral performance in a self-paced repetitive pressing and releasing task did not differ between groups. This finding demonstrates that the motor impairment of patients with PD
